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The spiroketal moiety is an important substructure within many biological natural products. One method to access them is via the oxidative cyclisation of a pendant hydroxyl group on to a pre‐formed pyran. However applications of this methodology have been severely limited by requiring the use of toxic oxidants, such as lead (IV) tetraacetate or mercuric oxide. Herein we report a high yielding photochemical route to prepare complex spiroketals using an oxidative photochemical approach employing iodine monochloride and sodium acetate and demonstrate the methodology to the synthesis of a number of insect pheromones. [ABSTRACT FROM AUTHOR]

Synthesis of renewable isoprene continues to attract significant interest, yet catalysts still need improvement for industrial applications. We report herein an efficient and novel Prins tandem approach for highly selective production of isoprene from bio‐based methanol and isobutene over Mo‐Fe−O and MgO/Mg(OH)2 acid‐base bifunctional catalysts. Hydration decreases the number of strong basic sites O2− ions and increases OH groups over MgO, thus improving the isoprene selectivity. Basic OH on Mg(OH)2 promotes the Prins condensation of formaldehyde and isobutene, while acidic OH promotes dehydration of isoprenol to isoprene. Suitable contents and proportions of basic and acidic OH groups over Mg(OH)2 increase isoprene selectivity and methanol conversion to 90 and 92 % on the Mo‐Fe−O+Mg(OH)2 composite catalysts, respectively. It exhibits good recycling stability, with isoprene selectivity remaining 90 % after five successive regenerations. DFT calculations reveal OH groups formed after hydration reduce the energy barrier of the H transfer step, thereby promoting the overall reaction. [ABSTRACT FROM AUTHOR]

The reaction solvent and catalyst play essential roles in the Prins reaction for the synthesis of 3-methyl-3-buten-1-ol (MBO) from formaldehyde and isobutene. The reactivity of the solid base-catalyzed Prins condensation reaction by formaldehyde and isobutene in supercritical CO2 was investigated using CsH2PO4-modified HZSM-5. We found that the alkaline sites of the alkali-loaded catalyst could extract the α-H on isobutene to generate olefin carbon-negative ions, while the supercritical CO2 with weak Lewis acidity could activate formaldehyde to carbon-positive ions, which can combine more easily with carbon-negative isobutene to react, thus improving the reactivity of the reaction system. [ABSTRACT FROM AUTHOR]

A catalytic diastereoselective Prins reaction for hydroxymethylation and hydroxylation of 1,3-diarylpropene was successfully utilized to prepare various 1,3-dioxanes 7 in 14–88% yields. Take advantage of the synthetic intermediate 7h, the key B/C rings in brazilin core could be constructed by the sequential of Friedel–Crafts/Ullmann-Ma rather than Ullmann-Ma/Friedel–Crafts reactions. [ABSTRACT FROM AUTHOR]

We improved our previous theoretical method for prediction of the catalytic activity of porous materials, which is based on the concept of transition state shape selectivity. This method used adsorption energy calculations for transition state (TS) with «frozen» (only the placement of TS inside the pore is optimized) structure on porous materials with molecular mechanics (MM) as a calculational method. Our improvement consists of application of semi-empirical methods with dispersion correction (e.g., PM3-D3 or PM6-D3H4) instead of MM. We found that with semi-empirical methods adsorption energy dependences on pore diameter are similar to dependences obtained by MM, and also semi-empirical methods predict the same value of the cavity diameter, at which there is a maximum of TS adsorption energy. Despite these similarities in obtained results, semi-empirical methods have the advantages that they can more accurately describe structures, intermolecular interactions and energy values. We have shown that the level of theory (PM3-D3 or RI-MP2/ma-def2-SVP) used for TS structure search, in the case of suggested method, has little effect. [ABSTRACT FROM AUTHOR]

The Ganoderma meroterpenoids are a growing class of natural products with architectural complexity, and exhibit a wide range of biological activities. Here, we report an enantioselective total synthesis of the Ganoderma meroterpenoid (‒)-lucidumone. The synthetic route features several key transformations, including a) a Cu-catalyzed enantioselective silicon-tethered intramolecular Diels-Alder cycloaddition to construct the highly functionalized bicyclo[2.2.2]octane moiety; b) Brønsted acid promoted tandem O-deprotection/Prins cyclization/Cycloetherification sequence followed by oxidation to install concurrently the tetrahydrofuran and the fused indanone framework; c) Fleming-Tamao oxidation to generate the secondary hydroxyl; d) an iron-catalyzed Wacker-type oxidation of hindered vinyl group to methyl ketone. The Ganoderma meroterpenoids are a growing class of natural products with a wide range of biological activities. Here, the authors report the enantioselective total synthesis of the Ganoderma meroterpenoid (‒)-lucidumone, featuring a copper-catalyzed enantioselective silicon-tethered intramolecular Diels-Alder cycloaddition to assemble the bicyclo[2.2.2]octane framework and a domino deprotection/Prins reaction/cycloetherification/oxidation sequence to generate concurrenly the tetrahydrofuran and the fused indanone skeleton. [ABSTRACT FROM AUTHOR]

We have achieved the first total synthesis of bipolarolides A and B, which possess an intriguing and complex 5/6/6/6/5 caged pentacyclic skeleton with seven contiguous stereocenters. The synthesis features a lithium‐halogen exchange/intermolecular nucleophilic addition to link two enantioenriched fragments, two ring‐closing metathesis reactions to assemble the five‐ and eight‐membered rings, and a bioinspired Prins reaction/ether formation cascade cyclization to construct the 5/6/6/6/5 caged skeleton. [ABSTRACT FROM AUTHOR]

A TfOH-promoted, metal-free protocol has been unveiled for the synthesis of spiro-furan quinazolinones employing alkynol urea derivatives utilizing alkynyl Prins cyclization reaction. This methodology produces highly functionalized spiro-heterocycles in excellent yields with exclusive E-selectivity under ambient conditions. Furthermore, late-stage modifications incorporate bromide and acetyl functionalities into the synthesized spiro-heterocycles. [ABSTRACT FROM AUTHOR]

An asymmetric formal synthesis of (+)‐phomactin A has been accomplished. The key steps in the synthetic strategy included establishing the AB ring system in one‐pot via Prins/Conia‐ene cascade cyclization reaction and the C ring formation via γ‐hydroxylation of enone in the late‐stage of the synthesis. The two major fragments are readily prepared from (+)‐pulegone and geraniol via a modified Eschenmoser–Tanabe fragmentation strategy in 6 steps and a Sharpless asymmetric epoxidation/hydrozirconation/ Roskamp reaction sequence in 11 steps respectively. [ABSTRACT FROM AUTHOR]

One-step gas-phase synthesis of butadiene from formaldehyde and propylene on aluminum (AlP), zirconium (ZrP), and niobium (NbP) phosphates with the pore volumes of 0.51, 0.25, and 0.19 cm3/g, respectively, was studied for the first time. The physicochemical properties of the catalysts were studied by X-ray fluorescence analysis, low-temperature nitrogen adsorption, X-ray diffraction analysis, scanning electron microscopy, temperature-programmed NH3 desorption, IR spectroscopy of adsorbed pyridine, and 31Р MAS NMR. Evaluation of the catalytic properties of the phosphates showed that they can be ranked in the following order with respect to the formaldehyde conversion and target product (butadiene) formation selectivity: AlP < ZrP < NbP, which correlates with metal electronegativity series. The СН2О conversion on the most active NbP was 4.5%, and the molar selectivity of the butadiene formation was 45.3%. [ABSTRACT FROM AUTHOR]

The synthetic methods of 2,3‐disubstituted benzofurans have been widely studied, however, the maneuvers of using o‐alkenyl phenols as starting materials are less explored. Herein, we report a general and efficient strategy via HNTf2/TMSOTf catalyzed cascade reaction with readily available o‐alkenyl phenols and aldehydes as starting materials, which provides 2,3‐disubstituted benzofuran derivatives in moderate to good yields. This method features metal‐free circumstances, broad substrate scope, mild reaction conditions, and easy scale preparation. [ABSTRACT FROM AUTHOR]

A variety of oxygen, nitrogen and sulfur heterocyclic compounds are synthesized via one-pot multicomponent Prins, aza-Prins, thia-Prins, oxonium-ene, iminium-ene and thionium-ene cyclization reactions. The reactions proceeds with high diastereo- and regioselectivity. Importantly, C–C, C–N, C–O and C–S bonds are formed in a singsle step. These procedures are extended for the synthesis of biologically active molecules and natural products. 1 Introduction 2 Prins Cyclization Reactions 3 Oxonium-Ene Cyclization Reactions 4 Conclusion [ABSTRACT FROM AUTHOR]

This study investigated the activity of H-MFI catalysts modified by the top-down method in the liquid-phase Prins reaction between propene and formaldehyde. The physicochemical characterization of the catalyst demonstrated that grinding the catalyst reduces the specific surface area and affects the micropore to mesopore ratio in the samples. Reducing the grain size was found to increase the initial substrate consumption rate and reduce the diffusion limitations in the system. At the same time, grinding shifts the product composition towards a higher proportion of byproducts. An assessment of the kinetic curves enabled the researchers to propose a number of equations that accurately reflect catalyst deactivation. Both the reaction rate and deactivation rate vary directly with the zeolite dispersion, while the deactivation of the sample is more sensitive to the grain size. [ABSTRACT FROM AUTHOR]

Small-molecule aldehydes are promising additives to regulate product distribution in methanol-to-hydrocarbon (MTH) reaction. Herein, the co-feeding of C 1 -C 4 aldehydes with methanol resulted in a significant increase in aromatic formation with the order: acetaldehyde > formaldehyde > propanal ≈ butanal. The mechanistic basis for this enhancement in aromatic production derived from both a direct participation pathway of aldehydes and an indirect pathway via driving the aromatic-based cycle. C 2+ aldehydes could undergo multiple aldol-condensation on Brønsted acid sites to form larger alkenals, followed by sequential cyclization-dehydration reaction to cycloalkenes or aromatic species. The Prins reaction could be extended to all C 1 -C 4 aldehydes with alkenes by generating the corresponding dienes. The hydrogen transfer from methanol to C 2+ aldehydes produced C 2+ olefins and formaldehyde, which would lead to extra formaldehyde-mediated aromatic formation pathway. The intricate evolution pathway of C 1 -C 4 aldehydes in MTH reaction was constructed by detecting abundant oxygenate and hydrocarbon intermediates. [Display omitted] • The co-feeding of C 1 -C 4 aldehydes with methanol increased the aromatic selectivity. • A direct and an indirect pathway promoted synchronously the aromatic formation. • In situ detecting abundant oxygenate and H-poor hydrocarbon intermediates. • The co-feeding of C 1 -C 4 aldehydes induced at least four-type reactions. • The evolution mechanism of C 1 -C 4 aldehydes was illustrated. [ABSTRACT FROM AUTHOR]

The spiroketal moiety is an important substructure within many biological natural products. One method to access them is via the oxidative cyclisation of a pendant hydroxyl group on to a pre‐formed pyran. However access to such precursors has hitherto been challenging and requires multistep syntheses frequently with considerable protecting group manipulation. Herein we report a novel and high yielding method for the preparation of hydroxydi‐ and hydroxytetra‐hydropyrans, as spiroketal precursors, utilizing a novel double‐Prins cyclisation approach. [ABSTRACT FROM AUTHOR]

Starting from readily available cyclic homoallylic alcohols, a Prins reaction allowed the formation of a bicyclic tetrahydropyranyl carbocation intermediate that is only trapped by electron-rich aromatic rings according a further intramolecular Friedel–Crafts reaction leading to new [4.4.3]propellane structures. [ABSTRACT FROM AUTHOR]

The paper describes linear optimization of process conditions for condensation of tert-butanol with aqueous formaldehyde in the presence of synthetic zeolites (CA-Y, NaA-Y, CaA-Y, NaX, and CaX) and phosphoric acid as catalysts. The process was carried out in an autoclave at 100–150°C, 0.5–0.6 MPa, and a stirring speed of 60 rpm. The selectivity towards 4,4-dimethyl-1,3-dioxane (DMD) as a target product in the Prins reaction involving tert-butanol was investigated as a function of optimization parameters such as reaction time, temperature, reactant ratio, phosphoric acid content, and synthetic zeolite type. For each "parameter vs. DMD selectivity" function, an extremum point corresponding to the optimal parameter value was found. In the presence of NaA-Y, the DMD selectivity reached 98%. [ABSTRACT FROM AUTHOR]

It is well known that zeolites exhibit catalytic activity in the Prins reaction. It was found that their use makes it possible to increase the selectivity of the Prins reaction with 2-methylpropene, and the dependences of the effective rate constants of the consumption of formaldehyde and the accumulation of 4,4‑dimethyl-1,3-dioxane on the pore diameter of zeolites are extremal. This work is relevant because the knowledge of the kinetics of the Prins reaction in the presence of type A and X zeolites can contribute to the regulation of selectivity for the formation of oxygen-containing compounds, in particular, industrially valuable 4,4-dimethyl-1,3-dioxane upon the interaction of formaldehyde and 2-methylpropene. [ABSTRACT FROM AUTHOR]

The natural products having tetrahydropyran unit with multiple chiral centers serve as magnificent building blocks for various active pharmaceutical ingredients (APIs). 'Prins cyclization is one of the wonderful strategies to construct tetrahydropyran unit stereoselectively in asymmetric synthesis. In this account, we discuss our research efforts toward the synthesis of various natural products from the past two decades (2005–2020) by using Prins cyclization as a key step. Further, the synthetic utility of this reaction was investigated and well demonstrated on various molecules successfully. [ABSTRACT FROM AUTHOR]

This study investigated the effects of reaction conditions in a one-step gas-phase synthesis of butadiene from formaldehyde and propylene over a SiO2-supported silicotungstic heteropoly acid catalyst. The physicochemical properties of the catalyst were examined by X-ray fluorescence spectroscopy, low-temperature nitrogen adsorption, XRD, SEM, and NH3–TPD. It was found that, with increase in reaction temperature, the yield of butadiene passes through its maximum. Increasing the WHSV of the reactant feed lowers the formaldehyde conversion and enhances the butadiene selectivity. Raising the propylene to formaldehyde molar ratio increases the formaldehyde conversion, with the butadiene selectivity passing through its maximum. Finally, diluting the reactants with an inert gas barely affects the process performance. [ABSTRACT FROM AUTHOR]

The dioxane method for the isoprene production is a chemically two-stage process based on the splitting of 4,4-dimethyl-1,3-dioxane. The latter is synthesized by condensation of iso-C4H8 or tert-C4H9OH with CH2O (Prins reaction). One of the disadvantages of the considered method of isoprene synthesis is the formation of up to 30–40 wt % by-products (dihydropyrans, diols, unsaturated alcohols, etc.) at the stage of 4,4-dimethyl-1,3-dioxane synthesis. The insufficiently high selectivity of the 4,4-dimethyl-1,3-dioxane formation is due to the multichannel Prins reaction; therefore, a noticeable increase in the selectivity of the process cannot be achieved only by optimizing the currently implemented technological schemes of the dioxane method for the isoprene production. The parameters of the reaction of tert-С4H9OH with CH2O in the presence of carbon-containing porous materials were selected using the linear optimization method. It was found that the condensation of tert-C4H9OH with CH2O under catalysis conditions with both carbon nanotubes and porous glassy carbon can yield 4,4-dimethyl-1,3-dioxane with a selectivity of up to ~99 wt %. [ABSTRACT FROM AUTHOR]

The synthesis of homolimonenol by Prins condensation of limonene and paraformaldehyde over heterogeneous tin-based catalysts is reported for the first time. The tin supported MCM-41, SBA-15, and KIT-6 materials were prepared by incipient wetness impregnation method, using SnCl 2 ·2H 2 O as a tin precursor. The synthesized catalysts were characterized by N 2 -physisorption, X-ray diffraction (XRD), diffuse reflectance-infrared Fourier transform spectroscopy (DRIFTS), pyridine adsorption (Py-FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and chemical analysis. Sn4+ species were identified on the surface of the catalysts, and the materials showed mainly Lewis acid sites, which are responsible for the activity in the Prins reaction. Production of homolimonenol was confirmed by GC-MS and NMR analysis. Among the evaluated catalysts, the best conversion (26%), selectivity (90%) and TOF (12.7 h−1) were obtained over Sn-SBA-15, in the presence of ethyl acetate; Sn-SBA-15 catalyst was reused five times without loss of activity. The reaction was scaled up from 2 to 200 mL glass reactor with a local orange oil (93% wt/wt limonene) as a substrate, obtaining a 30% conversion of limonene and a 93% selectivity to homolimonenol. [Display omitted] • Novel application of tin-supported mesoporous catalysts for homolimonenol synthesis. • Sn4+ species on the surface were identified by XPS, acidity was mainly Lewis. • Homolimonenol from oxyfunctionalization of a sample of orange oil. • Sn-SBA-15 catalyst can be reused up to 5 times without loss of activity. [ABSTRACT FROM AUTHOR]

This study investigated the kinetic patterns of the liquid-phase Prins condensation of propylene with formaldehyde in the range of 120–180°C over H–MFI and H–BEA zeolites. The apparent reaction order with respect to formaldehyde was found to vary between 0.1 and 0.2 for H–BEA and to be close to zero for H–MFI. The apparent activation energy for H–MFI and H–BEA was 26.1±0.6 kJ/mol and 20.0±4.0 kJ/mol, respectively. Based on these results, the reaction was demonstrated to occur in the intradiffusion or transition region; the calculated Thiele modulus and effectiveness factor further confirmed this fact. The diffusion limitations were partially removed by raising the initial formaldehyde concentration, as indicated by an increase in the apparent order of formaldehyde conversion to 1.0 for H–BEA and to 0.4 in the H–MFI case. To describe the substrate transformations observed, a modernized reaction mechanism was proposed. [ABSTRACT FROM AUTHOR]

The σ 1 receptor plays a key role in the regulation of various processes in the human body; it is involved in the development of neurodegenerative and neuropsychiatric diseases and is overexpressed in several human tumors rendering it an important target for potential drug candidates. In this project, spirocyclic σ 1 receptor ligands with different substituents in 4- and 9-position were synthesized and investigated for their σ 1 receptor affinity and selectivity over related targets. The σ 1 affinity of the ligands was correlated with their lipophilicity (log D 7.4 value) giving insight into their lipophilic ligand efficiency (LLE). The (pyridin-3-yl)methyl derivative 5i showed a promising balance of high σ 1 affinity (K i (σ 1) = 3.9 nM) and selectivity (>250-fold) as well as high LLE of 5.8. 5i has a high plasma protein binding (89 %) and promising metabolic stability in the presence of mouse liver microsomes and NADPH (83 % intact after 90 min). Increasing the size of the piperidine ring of the spirocyclic ligands 5 to an azepane ring led to considerably increased σ 1 affinity (K i (5a) = 1.2 nM, K i (23a) = 0.42 nM) and selectivity over σ 2 receptors (5a : 45-fold, 23a : 150-fold). [Display omitted] • Tetrahydropyrans with a spirocyclic attached piperidine or azepane ring as novel σ 1 ligands. • Key steps of the synthesis are a Prins reaction and a Suzuki coupling. • Relationships between the structure and σ 1 affinity and selectivity are identified. • Pharmacokinetic parameters were determined. • Efficiency of the ligands with respect to their recorded lipophilicity (LLE) [ABSTRACT FROM AUTHOR]

The field of biomimetic synthesis seeks to apply biosynthetic hypotheses to the efficient construction of complex natural products. This approach can also guide the revision of incorrectly assigned structures. Herein, we describe the evolution of a concise total synthesis and structural reassignment of hyperelodione D, a tetracyclic meroterpenoid derived from a Hypericum plant, alongside some biogenetically related natural products, erectones A and B. The key step in the synthesis of hyperelodione D forms six stereocentres and three rings in a bioinspired cascade reaction that features an intermolecular Diels–Alder reaction, an intramolecular Prins reaction and a terminating cycloetherification. [ABSTRACT FROM AUTHOR]

The Account describes recent advances, from the authors' laboratories, in the synthesis of diverse libraries of small-molecule building blocks employing ionic liquids (ILs). The ability of ILs to act as catalysts/promoters/solvents for electrophilic and onium ion chemistry, as well as in metal-mediated cross-coupling reactions, and the potential to sequence/hyphenate these methods, have opened up new opportunities for facile assembly of functional small molecules with increased complexity from readily available precursors. While Brønsted acidic IL/IL solvent mixtures are suitable media for carbocation and onium ion chemistry, piperidine-appended IL/IL solvent mixtures can successfully catalyze a variety of base-catalyzed reactions. Several widely practiced transformations including 'name reactions' were adapted and performed efficiently in ILs. 1 Introduction 2 Aryldiazonium Salts and Aryltriazenes as Coupling Partners in Metal-Mediated C–C Cross-Coupling Reactions in ILs 3 Expanding the Scope of Metal-Mediated Cross-Coupling Reactions in ILs 4 Application of ILs in Synthesis and Functionalization of Hetero-cycles 5 Expanding the Scope of Amide Synthesis in ILs 6 Generation and Chemistry of 'Tamed' Propargylic Cations in ILs 7 Newer Nitration Methods for Arenes and Heteroarenes in ILs 8 Halofunctionalization in ILs 9 'Name Reactions'and Other Widely Practiced Synthetic Transformations in ILs 9.1 The Biginelli Reaction 9.2 Nitrile Synthesis by the Schmidt Reaction 9.3 Rupe Rearrangement 9.4 Synthesis of 1,3-Dioxanes via Prins Reaction in [BMIM(SO3 H)][OTf] 9.5 Synthesis of Cyclopropanes and Oxiranes by the Corey–Chaykovsky (CC) Reaction 10 Conclusions and Closing Remarks [ABSTRACT FROM AUTHOR]

Several types of modified zeolite BETA38 with different iron loading were prepared. Prepared materials were characterized using different techniques (XRD, XRF, BET, UV–VIS, TPD, TPR, laser light scattering) with the focus on iron species types present in prepared materials. Catalytic activity of prepared materials was evaluated in lauric acid esterification with methanol, acetalization of heptanal with ethylene glycol and Prins reaction of isoprenol with butanal or benzaldehyde. A significant increase in material catalytic activity was observed after modification with iron in all cases, and no significant influence of iron amount on catalytic activity was observed. Material with 1wt% Fe loading provided > 90% conversion of reactants in case of esterification and acetalization (5 h). In Prins cyclization of benzaldehyde with isoprenol, the significant increase (fivefold, 40% increase) in achieved conversion was observed using Fe loaded Beta 38, whereas the increase was only slight (15% increase) in the reaction of butanal with isoprenol. Moreover, the possibility of catalyst reuse was confirmed. [ABSTRACT FROM AUTHOR]

A thermodynamic analysis of the reactions for the conversion of dimethyl ether into valuable products of the gas and oil industry and of propylene, formaldehyde, and 1,3-butadiene in particular was carried out. The temperature dependence of the equilibrium composition in the reaction for the production of 1,3-butadiene from dimethyl ether was determined. Calculation of the temperature dependence of the equilibrium composition in the reaction of propylene with formaldehyde with the formation of 1,3-dioxane, 1,3-butanediol, and 2-buten-1-ol showed that the main product at equilibrium is 2-buten-1-ol. [ABSTRACT FROM AUTHOR]

A series of micro-mesoporous polymeric ionic liquids (PILs) have been successfully synthesized by the method of anion and cation copolymerization. Then use FT-IR, N2 adsorption–desorption isotherms, SEM, and TG to characterize them. Furthermore, the catalytic performance of the synthesized PILs was investigated for the Prins reaction of propylene with 1, 3, 5-trioxane. Among the four PILs synthesized, VIMBs-DVB-SSA has better catalytic activities for the Prins reaction. Under the optimal conditions, 100 °C, 8 wt%, 4 h and n (propylene)/n (1, 3, 5-trioxane) = 4:1, the conversion of formaldehyde (99.8%) and selectivity (81.7%) for 4-methyl-1, 3-dioxane. In addition, the effects of reaction time, catalyst dosage, and reaction temperature and mole ratio of reaction substrates on the reaction were also investigated. The prepared catalyst had good thermal stability and can be reused easily.

1,3-Butanediol is an intermediate to produce products and can be used in chemical industry, medicine, and cosmetic. The paper summarizes the production of 1, 3-butanediol by two chemical syntheses, including acetaldehyde aldol condensation and hydrogenation, formaldehyde propylene condensation hydrolysis via Prins reaction. The research directions of the two processes in the future are also suggested. [ABSTRACT FROM AUTHOR]

Pd-catalyzed β-carbon elimination of 3-hydroxy-4-pent-enoic acid derivatives promoted by triethylborane proceeds to form conjugated dienes via a decarboxylation process. The formed conjugated dienes undergo the Prins reaction with aldehydes in situ to afford conjugated homoallylic alcohols. These sequential transformations enable the conversion of diastereomeric mixtures of 3-hydroxy-4-pentenoic acids, which are readily prepared from the simple crossed aldol reaction of esters and α,β-unsaturated aldehydes, into 3,5-hexadienyl alcohols with high regio- and stereoselectivities in a single manipulation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Colombian sodium silicate is a promising silicon source to synthesize MCM-41. • Two Sn incorporation methods were tested in catalyst synthesis. • Sn/MCM-41 with Na 2 SiO 3 is highly active (TOF =476 h−1) to nopol synthesis. • An alternative low cost paraformaldehyde was effectively used. • Paraformaldehyde polymerization degree affect activity of nopol synthesis. Colombian sodium silicate was used as silicon source in the synthesis of MCM-41 with several surfactant: SiO 2 molar ratios (MR = 0.12, 0.30, 0.50 and 0.70). Sn was incorporated on MCM-41 by incipient impregnation and by wetness impregnation using a rotaevaporador. The materials were characterized by AAS, XRD, N 2 adsorption-desorption isotherms, TEM, adsorption of pyridine, NH 3 -TPD, UV–vis-DRS and XPS. Materials with Na 2 SiO 3 (MR = 0.70) showed crystalline, textural and structural properties very similar to MCM-41 synthesized with tetraethyl orthosilicate (TEOS). The highest total acidity of materials synthesized with Na 2 SiO 3 compared with materials synthesized with TEOS could be owing to the use of sulfuric acid in the synthesis or the presence of more silanol groups in the solid surface. TOF values obtained in nopol production over materials synthesized with TEOS and Na 2 SiO 3 (MR = 0.70), using wetness impregnation with rotoevaporation, were 420 and 476 h−1, respectively. Low cost paraformaldehyde with larger polymerization degree than Sigma-Aldrich source of formaldehyde was characterized by XRF, XRD, FTIR, TGA and DSC. Polymerization degree seems to affect TOF for nopol production; lower TOF values were obtained with paraformaldehyde with larger polymerization degree. Depolymerization occurs by two parallel reactions: Avrami-Erofeyev (A4) and contracting area (R2) models, with activation energies of 19.8 and 77.5 kJ mol−1, respectively. Sn-MCM-41 synthesized with Na 2 SiO 3 can be used four times without considerable loss of catalytic activity; furthermore, no Sn leaching was detected. [ABSTRACT FROM AUTHOR]

• Kaurenoic or beyerenoic acid as substrates to explore stereoselective Prins reaction. • Quirality from natural diterpenes directly influences the Prins-cyclization process. • Highly stereoselective Prins-cyclization in diterpene skeletons favors fused oxane ring. • The mechanism of Prins-cyclization is proposed and supported by computational means. • Cytotoxic potential of kauroxane and beyeroxane is explored in vitro assays. A semisynthetic strategy to access novel kauroxane or beyeroxane compounds from ent ‑kauranal or ent ‑beyerenal, respectively, is described. A Prins cyclization was used as a key step reaction to synthesize diterpene-tetrahydropyran hybrid compounds with high stereoselectivity by using 3-buten-1-ol as oxane precursor and indium trichloride as the Lewis acid catalyst. The absolute configurations of new compounds were determined by mechanistic means and supported with DFT calculations, as well as considering the stereoselectivity behavior associated with the chiral purity of diterpenes and their conformational restrictions. The structures were elucidated by their physical and spectroscopic data. Finally, the antiproliferative activity of the target molecules was done, being moderately bioactive. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Intramolecular cyclization of enol ethers mediated by para-toluenesulfonic acid leads to substituted tetrahydropyrans in good to moderate yields. The reaction is diastereoselective.

The reaction solvent and catalyst play essential roles in the Prins reaction for the synthesis of 3-methyl-3-buten-1-ol (MBO) from formaldehyde and isobutene. The reactivity of the solid base-catalyzed Prins condensation reaction by formaldehyde and isobutene in supercritical CO 2 was investigated using CsH 2 PO 4 -modified HZSM-5. We found that the alkaline sites of the alkali-loaded catalyst could extract the α-H on isobutene to generate olefin carbon-negative ions, while the supercritical CO 2 with weak Lewis acidity could activate formaldehyde to carbon-positive ions, which can combine more easily with carbon-negative isobutene to react, thus improving the reactivity of the reaction system., Competing Interests: Competing interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© TÜBİTAK.)

Turpentine is a mixture of monoterpene hydrocarbons obtained as a by-product in the paper industry. In this contribution we present its transformation process towards an alcohol named nopol, that is an important household product and fragrance raw material. Reaction conditions were established for the oxyfuntionalization of crude turpentine oil over Sn-MCM-41 catalyst for the selective conversion of β-pinene to nopol. Synthesized materials were characterized by XRD, N2 adsorption, FT-IR, TEM and chemical absorption. The reaction was tested in 2 mL glass reactor with a sample of commercial turpentine with α-pinene (55.5% w/w) and β-pinene (39.5% w/w) as main components and scaled up into a 100 mL Parr reactor, getting 92% conversion of β-pinene and a nopol selectivity of 93%. The reusability tests showed that the catalyst can be reused 4 times without loss of activity. The results showed that 86% less solvent and 37.5% less paraformaldehyde can be used with turpentine, compared to the conditions used with β-pinene for getting similar catalysts activity.

A flow synthesis method of (E)-2-hexenal intermediates by employing a two-stage microreactor system was reported as an example of autothermal Prins-type reaction. The continuous flow technology not only overcame the low efficiency of batch reactions, it also met the demand for high selectivity and required less consumption of reactants. Temperature monitors of a micro-mixer and a reaction tube covered by thick thermal insulation materials provided an apparent reaction enthalpy of −112 kJ·mol−1 for the generations of hexenal intermediates and by-products. A two-stage reaction platform was therefore developed to enable efficient control of the reaction temperature, which was from 20 °C and 110 °C. Under optimized operating conditions, the yield of (E)-2-hexenal intermediates reached 72%, with a space time yield of 273 kg·h−1 L−1, which was over 1200 times that of a traditional batch reactor with dripping fed reactants. The final yield of (E)-2-hexenal was maintained at 72% after hydrolysis of the intermediates. [ABSTRACT FROM AUTHOR]

A series of micro-mesoporous polymeric ionic liquids (PILs) have been successfully synthesized by the method of anion and cation copolymerization. Then use FT-IR, N 2 adsorption–desorption isotherms, SEM, and TG to characterize them. Furthermore, the catalytic performance of the synthesized PILs was investigated for the Prins reaction of propylene with 1, 3, 5-trioxane. Among the four PILs synthesized, VIMBs-DVB-SSA has better catalytic activities for the Prins reaction. Under the optimal conditions, 100 °C, 8 wt%, 4 h and n (propylene)/n (1, 3, 5-trioxane) = 4:1, the conversion of formaldehyde (99.8%) and selectivity (81.7%) for 4-methyl-1, 3-dioxane. In addition, the effects of reaction time, catalyst dosage, and reaction temperature and mole ratio of reaction substrates on the reaction were also investigated. The prepared catalyst had good thermal stability and can be reused easily. [ABSTRACT FROM AUTHOR]

Nopol (2-(6,6-dimethyl-2-bicyclo[3.1.1]hept-2-enyl)ethanol) is an important fragrant compound, which synthesis is widely studied. Possibility of the use of heterogeneous catalysts instead of commonly used zinc (II) chloride can offer environmentally friendly process with possible catalyst reuse and avoiding wastewater production. Several metal modified SiO2 materials (mostly molybdenum, tungsten and zinc) were prepared and tested in nopol synthesis. Molybdenum and zinc modified material (with 25 wt% of MoO3 resp. ZnO loading) showed to possess a high activity in nopol synthesis accompanied by high selectivity of nopol formation. Under optimal reaction conditions (solvent benzonitrile, 80 °C, molar ratio β-pinene:paraformaldehyde = 1:2, 24 h) following results were observed: using catalyst 25 wt% MoO3–SiO2 (20 wt% to β-pinene) 77% β-pinene conversion and 98.7% selectivity of nopol formation was obtained (24 h), using catalyst 25 wt% ZnO–SiO2 (40 wt% to β-pinene) 72% β-pinene conversion and 96.3% selectivity of nopol formation was obtained (24 h). Molybdenum or zinc modified SiO2 can be successfully used in nopol synthesis from β-pinene and paraformaldehyde as heterogeneous catalysts, after material regeneration, the catalyst reuse is possible. [ABSTRACT FROM AUTHOR]

Several types of mixed WO3/SiO2/Al2O3 materials were prepared using sol–gel and wet impregnation methods. Four different loadings of WO3 (1, 10, 25 and 40 wt%) were prepared. Materials were characterized using X-ray diffraction, X-ray fluorescence spectroscopy, and their acidity was measured by temperature programmed desorption of pyridine. Catalytic activity of these materials was tested in Prins reaction—intramolecular cyclization of citronellal. Influence of reaction conditions (temperature 70–90 °C, catalyst amount 1–10 wt%, catalyst type) on citronellal conversion and selectivity of isopulegol formation was monitored. The best result (90% of isopulegol, 97% selectivity of isopulegol formation, 24 h) was obtained using W25 IMP catalyst (10 wt%, 50 °C). Possibility of catalyst reuse was confirmed. [ABSTRACT FROM AUTHOR]

A single-stage gas-phase synthesis of isoprene from formaldehyde and isobutylene in the presence of Al–BEA and Nb–BEA zeolite catalysts containing different amounts of aluminum and niobium has been studied. The physicochemical properties of the catalysts have been studied by low-temperature nitrogen adsorption, infrared spectroscopy of adsorbed CO, X-ray fluorescence analysis, and ammonia TPD methods. Catalytic tests have shown that, at similar formaldehyde conversion values, the isoprene selectivity is higher in the presence of the Al-containing BEA catalysts. It has been found that Al–BEA with Si/Al = 12 exhibits the highest activity in isoprene synthesis. [ABSTRACT FROM AUTHOR]

We have identified a switchable Prins cyclization process to form indoline‐fused tetrahydrofurans and indole‐fused oxepanes by applying different types of aldehydes under two sets of optimized conditions. Significantly, a novel Prins reaction mechanism involving an oxonium‐mediated rearrangement in the formation of five‐membered cyclic ethers is realized for the first time. [ABSTRACT FROM AUTHOR]

This review focuses on alkynyl Prins and alkynyl aza-Prins cyclization- processes, which involve intramolecular coupling of an alkyne with either an oxocarbenium or iminium electrophile. The oxocarbenium or iminium species can be generated through condensation- or elimination-type processes, to achieve an overall bimolecular annulation that enables the synthesis of both oxygen- and nitrogen-containing- saturated heterocycles with different ring sizes and substitution patterns. Also discussed are cascade processes in which alkynyl Prins heterocyclic adducts react to trigger subsequent pericyclic reactions, including [4+2] cycloadditions and Nazarov electrocyclizations, to rapidly construct complex small molecules. Finally, examples of the use of alkynyl Prins and alkynyl aza-Prins reactions in the synthesis of natural products are described. The review covers the literature through the end of 2019. 1 Introduction 1.1 Alkyne-Carbonyl Coupling Pathways 1.2 Coupling/Cyclization Cascades Using the Alkynyl Prins Reaction 2 Alkynyl Prins Annulation (Oxocarbenium Electrophiles) 2.1 Early Work 2.2 Halide as Terminal Nucleophile 2.3 Oxygen as Terminal Nucleophile 2.4 Arene as Terminal Nucleophile (Intermolecular) 2.5 Arene Terminal Nucleophile (Intramolecular) 2.6 Cyclizations Terminated by Elimination 3 Synthetic Utility of Alkynyl Prins Annulation 3.1 Alkynyl Prins-Mediated Synthesis of Dienes for a [4+2] Cyclo-- addition--Oxidation Sequence 3.2 Alkynyl Prins Cyclization Adducts as Nazarov Cyclization Precursors 3.3 Alkynyl Prins Cyclization in Natural Product Synthesis 4 Alkynyl Aza-Prins Annulation 4.1 Iminium Electrophiles 4.2 Activated Iminium Electrophiles 5 Alkynyl Aza-Prins Cyclizations in Natural Product Synthesis 6 Summary and Outlook [ABSTRACT FROM AUTHOR]

Ever since Hirata's report of yuzurimine in 1966, nearly fifty yuzurimine-type alkaloids have been isolated, which formed the largest subfamily of the Daphniphyllum alkaloids. Despite extensive synthetic studies towards this synthetically challenging and biologically intriguing family, no total synthesis of any yuzurimine-type alkaloids has been achieved to date. Here, the first enantioselective total synthesis of (+)-caldaphnidine J, a highly complex yuzurimine-type Daphniphyllum alkaloid, is described. Key transformations of this approach include a highly regioselective Pd-catalyzed hydroformylation, a samarium(II)-mediated pinacol coupling, and a one-pot Swern oxidation/ketene dithioacetal Prins reaction. Our approach paves the way for the synthesis of other yuzurimine-type alkaloids and related natural products. Despite being known for more than 50 years, yuzurimine-type alkaloids have not been accessed by total synthesis. Here, the authors report the first enantioselective total synthesis of (+)-Caldaphnidine J, a highly complex yuzurimine-type Daphniphyllum alkaloid. [ABSTRACT FROM AUTHOR]

The synthesis of fluorinated octahydro-2H-chromene was carried out using the Prins reaction between the monoterpenoid (–)-isopulegol and carbonyl compounds in the presence of the BF3·Et2O–H2O system, which acts as both an acid catalyst and a fluorine source. The use of the readily available and easy-to-use BF3·Et2O reagent makes this method of obtaining fluorine derivatives simple and practical. [ABSTRACT FROM AUTHOR]

This review considers heterogeneous catalysts for the Prins reaction. The potential of the industrial implementation of processes based on this reaction has been shown. The catalyst properties (textural and acidic) that have the greatest effect on the product composition are discussed. The most promising types of catalysts for preparing unsaturated alcohols and diene hydrocarbons are noted. [ABSTRACT FROM AUTHOR]

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The preparation of renewable isoprene from biomass-derivable feedstocks is extremely desirable for the sustainable rubber/latex/pharmaceutical industries. We report here a novel tandem route to efficiently produce isoprene via bio-sourced methanol and isobutene over Mo-Fe-O+meso-Cu/MgO composite catalysts. High isoprene selectivity of 85 % was achieved at methanol conversion of 91 % under optimal conditions. Adding Cu into mesoporous MgO finely tunes the basicity and acidity balance, thereby promoting isoprene selectivity. It shows good recycle capability, with isoprene selectivity remaining 85 % after five successive regeneration cycles. In-situ DRIFTS of methanol and isobutene adsorption suggest the possible reaction pathways involve methanol oxidation to formaldehyde on Mo-Fe oxide, followed by Prins condensation between formaldehyde and isobutene to isoprenol, and final conversion to isoprene on meso-Cu/MgO. This work not only represents a great advance in industrial large-scale producing isoprene, but provides an efficient strategy for developing methanol as in-situ precursor of formaldehyde to participate in many reactions. [Display omitted] • A novel tandem route defined by "Oxidative Prins Reaction" was proposed to produce isoprene over Mo-Fe-O+ meso -Cu/MgO. • The composite catalysts showed excellent performance, good recycle capability and stability in the oxidative Prins reaction. • A proper balance of basicity and acidity on the composite catalysts accounted for the high isoprene selectivity. • The possible reaction pathways of the oxidative Prins condensation could be: methanol→formaldehyde→isoprenol→isoprene. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ordered MPOM was prepared by high-temperature polymerization of [pPDA][2HSO 4 ]. • MPOM-T-AIL had high BET surface area, ordered mesoporosity, hydrophobic property. • MPOM-T-AIL exhibited much better catalytic performance than traditional acids. • The hydrophobic property of MPOM-T-AIL greatly enhanced its catalytic selectivity. Strong acidic ionic liquid-functionalized mesoporous organic material (MPOM-T-AIL) has been created by quaternary ammonization of mesoporous organic material (MPOM) with 1,3-propane sultone and subsequent strong acid (H 2 SO 4 or HSO 3 CF 3) acidification. The novel supporting material, MPOM, had high nitrogen content and was synthesized by direct high-temperature (400–550 °C) polymerization of an easily prepared and low cost protic salt [pPDA][2HSO 4 ], which was obtained by simple neutralization of p-phenylenediamine with two equivalents of H 2 SO 4. MPOM-T-AIL possesses high BET specific surface area, ordered and uniform mesoporosity, hydrophobic property, and highly active acidic ionic liquid components. Catalytic tests in the water-medium Prins reactions and acetalization of benzaldehyde with ethylene glycol showed that MPOM-T-AIL exhibits much better catalytic activities and reusabilities than commercially available solid acid catalysts Amberlyst 15 and H-ZSM-5, and mineral acid H 2 SO 4. Additionally, MPOM-T-AIL significantly improved the catalytic selectivity of the water-medium Prins reaction, which was strongly related to its hydrophobic property. MPOM-T-AIL with excellent catalytic performance is a promising new solid acid catalyst for various acid-catalyzed reactions. [ABSTRACT FROM AUTHOR]