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A sustainable method for the synthesis of 2-deoxy lactones as direct precursors to 2-deoxy sugars via regioselective UV-light-driven dealkyloxylation of carbohydrate-derived lactones is detailed. This catalyst- and additive-free protocol utilizes light irradiation, providing high step economy and functional group compatibility. This environmentally friendly and straightforward approach enhances the synthetic toolbox for 2-deoxy sugars, which is vital in numerous biologically active molecules and drug candidates.

Drastic changes to the character of the acidic catalyst enable the reversal of the double alkyne benzannulation reaction output. In the presence of a strong Brønsted acid, 1,4-dihydropyrrolopyrroles undergo transformation which results in the formation of two 7-membered rings. Computational studies imply that the thermodynamically unfavored 7-membered ring is forged via the kinetically favored 6-endo-dig attack of a protonated alkyne at the position 3a of pyrrolopyrrole followed by a 1,2-vinyl shift.

Tight chelation of enolate by lithium alters the selectivity of tandem palladium-catalyzed cyclization/coupling of terminal α-homopropargyl-β-ketoesters with aryl halides. In the presence of LiOH, substituted cyclopentenes are preferentially formed via 5- endo-dig carbocyclization, in contrast to the 6 -exo-dig oxocyclization exclusively observed in the absence of a hard, chelating metal center. The disclosed transformation, featuring mild conditions and broad functional group tolerance, can be applied for a variety of (hetero)aryl bromides as well as aryl and vinyl triflates.

Herein, we describe a simple three-coordinate complex of Cu(I) with an NHC and 1,10-phenanthroline ligands as an effective photocatalyst for energy (e.g., olefin E / Z isomerization) and electron transfer (e.g., aryl halide dehalogenation) reactions under blue-light irradiation. This complex can be obtained in a one-pot procedure starting from commercially available reagents and green solvents (EtOH, water). We hereby present a study of its activity and mechanistic insight into its mode of operation.

Under light irradiation, aryldiazo acetates can generate either singlet or triplet carbenes depending on the reaction conditions, but heteroaryl diazo compounds have remained underexplored in this context. Herein, we found that triazolyl diazoacetates exhibit higher reactivity than their aryl counterparts. They even react with dichloromethane (DCM), a common, inert solvent, for photoreactions involving diazo reagents, giving halogenated products. Theoretical studies show that all reactions involve carbenes but progress via different pathways depending on the solvent used., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Heterocyclic rings are important structural scaffolds encountered in both natural and synthetic compounds, and their biological activity often depends on these motifs. They are predominantly accessible via cycloaddition reactions, realized by either thermal, photochemical, or catalytic means. Various starting materials are utilized for this purpose, and, among them, diazo compounds are often encountered, especially vinyldiazo compounds that give access to donor-acceptor cyclopropenes which engage in [2+n] cycloaddition reactions. Herein, we describe the development of photochemical processes that produce diverse heterocyclic scaffolds from multisubstituted oximidovinyldiazo compounds. High chemoselectivity, good functional group tolerance, and excellent scalability characterize this methodology, thus predisposing it for broader applications. Experimental and computational studies reveal that under light irradiation these diazo reagents selectively transform into cyclopropenes which engage in cycloaddition reactions with various dipoles, while under thermal conditions the formation of pyrazole from vinyldiazo compounds is favored., (© 2024. The Author(s).)

An unprecedented DDQ-mediated oxidative aromatization of 2-bezylidene-dihydrofurans yielding 2-alkenyl-furans is disclosed. Integration of this transformation with a prior Pd-catalyzed reaction of α-propargylic-β-ketoesters and (hetero)aryl halides into a one-pot cascade process opens a direct modular route to highly substituted 2-vinyl-furans. Experimental and computational studies reveal that the crucial step of the oxidative-aromatization involves facile hydride transfer from the dihydrofuran ring to the O-center of DDQ.

The tandem intramolecular hydroarylation of alkynes accompanied by a 1,2-aryl shift is described. Harnessing the unique electron-rich character of 1,4-dihydropyrrolo[3,2-b]pyrrole scaffold, we demonstrate that the hydroarylation of alkynes proceeds at the already occupied positions 2 and 5 leading to a 1,2-aryl shift. Remarkably, the reaction proceeds only in the presence of cationic gold catalyst, and it leads to heretofore unknown π-expanded, centrosymmetric pyrrolo[3,2-b]pyrroles. The utility is verified in the preparation of 13 products that bear six conjugated rings. The observed compatibility with various functional groups allows for increased tunability with regard to the photophysical properties as well as providing sites for further functionalization. Computational studies of the reaction mechanism revealed that the formation of the six-membered rings accompanied with a 1,2-aryl shift is both kinetically and thermodynamically favourable over plausible formation of products containing 7-membered rings. Steady-state UV/Visible spectroscopy reveals that upon photoexcitation, the prepared S-shaped N-doped nanographenes undergo mostly radiative relaxation leading to large fluorescence quantum yields. Their optical properties are rationalized through time-dependent density functional theory calculations. We anticipate that this chemistry will empower the creation of new materials with various functionalities., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

A cascade of 5- exo-dig intramolecular nucleophilic addition of enamine to terminal alkyne followed by cross coupling has been demonstrated for the first time. Two new C-C bonds are stereoselectively forged by a single Pd-complex capable of catalyzing two mechanistically diverse transformations. Mechanistic investigations identified cyclization as the rate limiting step relying on the facile displacement of OTf, weakly bound to the Pd-center, by the alkyne.

Oxetanes are valuable building blocks due to their well-explored propensity to undergo ring-opening reactions with nucleophiles. However, their application as precursors of radical species is still elusive. Herein, we present a bioinspired cobalt-catalysis-based strategy to access unprecedented modes of radical reactivity via oxetane ring-opening. This powerful approach gives access to nucleophilic radicals that engage in reactions with SOMOphiles and low-valent transition metals. Importantly, the regioselectivity of these processes complements known methodologies.

We report a new method for a tandem Pd-catalyzed intramolecular addition of active methylene compounds to internal alkynes followed by coupling with aryl and heteroaryl bromides. Highly substituted vinylidenecyclopentanes were obtained with good yields, complete selectivity, and excellent functional group tolerance. A plausible mechanism, supported by DFT calculations, involves the oxidative addition of bromoarene to Pd(0), followed by cyclization and reductive elimination. The excellent regio- and stereoselectivity arises from the 5-exo-dig intramolecular addition of the enol form of the substrate to alkyne activated by the π-acidic Pd(II) center, postulated as the rate-determining step.

Ring-opening of epoxides furnishing either linear or branched products belongs to the group of classic transformations in organic synthesis. However, the regioselective cross-electrophile coupling of aryl epoxides with aryl halides still represents a key challenge. Herein, we report that the vitamin B 12 /Ni dual-catalytic system allows for the selective synthesis of linear products under blue-light irradiation, thus complementing methodologies that give access to branched alcohols. Experimental and theoretical studies corroborate the proposed mechanism involving alkylcobalamin as an intermediate in this reaction.

We report an efficient protocol for tandem Pd-catalyzed intramolecular addition of active methylene compounds to alkynes, followed by subsequent cross-coupling with (hetero)aryl bromides and chlorides. The reaction proceeds under mild conditions, providing excellent functional group tolerance, including unprotected OH, NH 2 groups, enolizable ketones, or a variety of heterocycles. Mechanistic studies point towards a catalytic cycle involving oxidative addition, intramolecular nucleophilic addition to the Pd(ii)-activated alkyne, and reductive elimination, with 5- exo-dig cyclization being the rate limiting step., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A three-component tandem Pd-catalyzed perfluoroalkylative borylation of terminal and internal alkynes is presented. On the basis of this methodology, the first reductive dicarbofunctionalization of alkynes with two electrophiles (perfluoroalkyl and aryl iodides) through a temperature-controlled sequence of iodoperfluoroalkylation-borylation coupling is developed. This regio- and stereoselective process is easily controllable by a temperature program, providing access to fluoroalkyl-substituted vinyl iodides, vinyl boronates, or olefins from the very same complex reaction mixture (four substrates, catalysts, base, and additives).

We report an efficient and functional group-tolerant method for the synthesis of substituted dihydropyrans, based on tandem Pd-catalyzed cyclization/coupling of δ-acetylenic β-ketoesters with aryl halides. The reaction proceeds cleanly through 6- exo-dig oxocyclizaton mode, delivering products with very good yields and complete control of regio- and stereoselectivity. Due to mild conditions, the transformation offers exceptional tolerance of functionalities, including NHR, formyl, enolizable ketone, free OH and NH 2 groups, as well as a range of N-heterocyclic moieties of potential biological relevance.

A four-component Pd-catalyzed protocol for direct synthesis of perfluoroalkyl-substituted enones is reported. Under mild conditions and low catalyst loading, alkynes, iodoperfluoroalkanes, (hetero)arylboronic acids, and carbon monoxide are assembled into highly elaborate products with good yields and excellent regio- and stereoselectivities. The configuration of the products was confirmed by the observation of through-space 13 C- 19 F couplings, accessible through the analysis of routine 13 C NMR spectra.

Metal salen complexes are one of the most frequently used catalysts in enantioselective organic synthesis. In the present work, we compare a series of ionization methods that can be used for the mass spectral analysis of two types of metalosalens: ionic complexes (abbreviated as Com(+)X(-)) and neutral complexes (NCom). These methods include electron ionization and field desorption (FD) which can be applied to pure samples and atmospheric pressure ionization techniques: electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) which are suitable for solutions. We found that FD is a method of choice for recording molecular ions of the complexes containing even loosely bonded ligands. The results obtained using atmospheric pressure ionization methods show that the results depend mainly on the structure of metal salen complex and the ionization method. In ESI spectra, Com(+) ions were observed, while in APCI and APPI spectra both Com(+) and [Com + H](+) ions are observed in the ratio depending on the structure of the metal salen complex and the solvent used in the analysis. For complexes with tetrafluoroborate counterion, an elimination of BF3 took place, and ions corresponding to complexes with fluoride counterion were observed. Experiments comparing the relative sensitivity of ESI, APCI and APPI (with and without a dopant) methods showed that for the majority of the studied complexes ESI is the most sensitive one; however, the sensitivity of APCI is usually less than two times lower and for some compounds is even higher than the sensitivity of ESI. Both methods show very high linearity of the calibration curve in a range of about 3 orders of magnitude of the sample concentration., (Copyright © 2014 John Wiley & Sons, Ltd.)

We report the Pd-catalyzed α-arylation of α,α-difluoroketones with aryl and heteroaryl bromides and chlorides catalyzed by an air- and moisture-stable palladacyclic complex containing P(t-Bu)Cy2 as ligand. The combination of this Pd-catalyzed arylation and base-induced cleavage of the acyl-aryl C-C bond within the α-aryl-α,α-difluoroketone constitutes a one-pot, two-step procedure to synthesize difluoromethylarenes from aryl halides. A broad range of electronically varied aryl and heteroaryl bromides and chlorides underwent these two transformations, providing α-aryl-α,α-difluoroketones, difluoromethylarenes, and difluoromethylheteroarenes in high yields.

Treat me gently: for a selective synthesis of the unusually sensitive cyclophanic α-pyrone neurymenolide A, the chosen catalysts must be able to distinguish between six different sites of unsaturation, without scrambling any of the skipped π systems. This challenge was met with a new gold-catalyzed pyrone synthesis in combination with a molybdenum-catalyzed ring-closing alkyne metathesis., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This paper presents a simple and efficient route to chiral cis-6-substituted 2-(2-hydroxyethyl)-5,6-dihydro-2H-pyrans, a versatile chiral building block. The strategy is based on three key transformations: enantioselective hetero-Diels-Alder (HDA) reaction of aldehyde with Danishefsky's diene, selective reduction of carbonyl function, and Claisen or related rearrangement. The synthetic utility of the methodology is illustrated by total synthesis of antibiotic (-)-centolobine.

This study investigates, experimentally and computationally, the role played by the structure of the diamine moiety of salen chromium complexes in determining the catalyst conformational equilibrium and, in consequence, the direction of asymmetric induction in metallosalen-catalyzed reactions of aldehydes.

The Friedel-Crafts reaction of (1R)-8-phenylmenthyl glyoxylate with variously substituted furans was found to be efficiently promoted by SnCl(4) or magnesium salts with high diastereoselectivities. MgBr(2) performs especially well under simple, undemanding conditions, giving both high yields and high diastereoselectivities (>90%). The reaction afforded chiral substituted furan-2-yl-hydroxyacetic acid esters, compounds of potentially high synthetic interest. [reaction: see text]