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The stereoselective formation of tetrasubstituted alkenes remains one of the key goals of modern organic synthesis. In addition to other methods, the stereoselective synthesis of tetrasubstituted alkenes can be achieved by means of cross-coupling reactions of electrophilic and nucleophilic alkene templates. The use of electrophilic templates for the stereoselective synthesis of tetrasubstituted alkenes has previously been described. Therefore, the present review summarizes the procedures available for the stereoselective preparation of tetrasubstituted alkenes using stable and isolable nucleophilic templates. [ABSTRACT FROM AUTHOR]

A readily available and bench-stable cyanomethyl sulfonium salt was used in highly diastereoselective Corey–Chaykovsky cyclopropanation reactions of electron-poor olefins. This efficient method provides a rapid route to access densely functionalized cyclopropyl nitriles. [ABSTRACT FROM AUTHOR]

Stereospecific β‐l‐rhamnopyranosylations were conducted using a 1,2‐anhydro‐l‐rhamnopyranose donor and mono‐ol or diol acceptors in the presence of a glycosyl‐acceptor‐derived borinic or boronic ester. Reactions proceeded smoothly to provide the corresponding β‐l‐rhamnopyranosides (β‐l‐Rhap) with complete stereoselectivity in moderate to high yields without any further additives under mild conditions. Mechanistic studies of the borinic ester mediated glycosylation using 13C kinetic isotope effect (KIE) measurements and DFT calculations were consistent with a concerted SNi mechanism with an exploded transition state. In addition, the present glycosylation method was applied successfully to the synthesis of a trisaccharide, α‐l‐Rhap‐(1,2)‐β‐l‐Rhap‐(1,4)‐Glcp, derived from Streptococcus pneumoniae serotypes 7B, 7C, and 7D. [ABSTRACT FROM AUTHOR]

Crossed aldol reactions of the CF3-containing pseudo C2 symmetric cyclic imide 3 were carried out by way of the corresponding boron bisenolate to stereoselectively furnish the desired products 4 and this procedure allowed the preferential construction of the diastereomers of the compounds previously obtained from the acyclic counterpart 1. [ABSTRACT FROM AUTHOR]

A Lewis acid-catalyzed [3 + 3] cycloaddition reaction of donor‒acceptor aziridines with N,N -dialkyl-3-vinylanilines has been developed for the stereoselective synthesis of tetrahydroisoquinolines (THIQs). The reaction performed using Gd(OTf) 3 as the Lewis acid catalyst was tolerant to various N -tosylaziridine and N,N -dialkyl-3-vinylaniline substrates and provided access to highly functionalized THIQs in typically high yields with moderate-to-excellent diastereoselectivities. [ABSTRACT FROM AUTHOR]

New series of trans - and cis -3-methylseleno substituted β-lactams ( 4 , 5 ) have been prepared from 2-methylselenoethanoic acid ( 2 ). The four-membered β-lactam ring was introduced by the condensation reaction between ketene retrieved from 2-methylselenoethanoic acid ( 2 ) and suitably substituted imines ( 3a-f) in the presence of triethylamine using POCl 3 in refluxing toluene. The structural and stereochemical analysis of novel trans - and cis -3-methylseleno substituted β-lactams were carried out using IR, NMR ( 1 H and 13 C), 2D-NMR ( 1 H– 1 H COSY, 1 H– 13 C HSQC), elemental analysis (CHN) and mass spectrometry (EIMS). Further, the structures of trans -1-(4′-methoxyphenyl)-3-methylseleno-4-(4′-chlorophenyl)azetidin-2-one ( 4b ), trans -1-(4′-methoxyphenyl)-3-methylseleno-4-(4′-methylphenyl)azetidin-2-one ( 4c ), trans - and cis -1-(4′-methoxyphenyl)-3-methylseleno-4-styrylazetidin-2-ones ( 4e and 5e ) were established by single crystal X-ray crystallographic studies. The cis or trans configuration of the hydrogen at C-3 was assigned with respect to C4-H. [ABSTRACT FROM AUTHOR]

1-Arylidene-2-tetralone (2), obtained from condensation of 2-tetralone and aromatic aldehydes in acetic acid and HCl, on condensation with thiosemicarbazide in acidic and alkaline medium afforded tetrahydro-2 H -benzo[ e ]indazole-2-carbothioamide as trans (3) and cis (4) diastereoisomers of 1- H and 9b- H respectively. The synthesis of new indazolyl-thiazol-4(5 H )-ones (5) from trans isomer (3) and α-halo acids is reported. A DFT study along with single crystal X-ray diffraction data of a representative compound (5a) is presented. The chemistry of the reaction of indazole-2-carbothioamides with methyl iodide, DMAD and acetic anhydride is described. Eight newly synthesised compounds were screened for their antibacterial and antifungal activities. Some of the compounds have shown promising antimicrobial activities. [ABSTRACT FROM AUTHOR]

Starting from readily available alkenyl methyl ethers, the stereoselective preparation of highly substituted alkenes by two complementary multicatalytic sequential isomerization/cross-coupling sequences is described. Both elementary steps of these sequences are challenging processes when considered independently. A cationic iridium catalyst was identified for the stereoselective isomerization of allyl methyl ethers and was found to be compatible with a nickel catalyst for the subsequent cross-coupling of the in situ generated methyl vinyl ethers with various Grignard reagents. The method is compatible with sensitive functional groups and a multitude of olefinic substitution patterns to deliver products with high control of the newly generated C=C bond. A highly enantioselective variant of this [Ir/Ni] sequence has been established using a chiral iridium precatalyst. A complementary [Pd/Ni] catalytic sequence has been optimized for alkenyl methyl ethers with a remote C=C bond. The final alkenes were isolated with a lower level of stereocontrol. Upon proper choice of the Grignard reagent, we demonstrated that C(sp²)-C(sp²) and C(sp²)-C(sp³) bonds can be constructed with both systems delivering products that would be difficult to access by conventional methods. [ABSTRACT FROM AUTHOR]

Although stereoselective antibody has immense potential in chiral compounds detection and separation, the interaction traits between stereoselective antibody and the corresponding antigenic enantiomers are not yet fully exploited. In this study, the stereospecific interactions between ofloxacin isomers and corresponding monoclonal antibodies (McAb-WR1 and McAb-MS1) were investigated using time-resolved fluorescence, steady-state fluorescence, and circular dichroism (CD) spectroscopic methods. The chiral recognition discrepancies of antibodies with ofloxacin isomers were reflected through binding constant, number of binding sites, driving forces and conformational changes. The major interacting forces of McAb-WR1 and McAb-MS1 chiral interaction systems were hydrophobic force and van der Waals forces joined up with hydrogen bonds, respectively. Synchronous fluorescence spectra and CD spectra results showed that the disturbing of tyrosine and tryptophan micro-environments were so slightly that no obvious secondary structure changes were found during the chiral hapten binding. Clarification of stereospecific interaction of antibody will facilitate the application of immunoassay to analyze chiral contaminants in food and other areas. [ABSTRACT FROM AUTHOR]

A lipase-catalysed two-step butanolytic desymmetrization process for the preparation of pyrazolidyl butyl (S)-2-methylmalonate from 2-methylmalonic dipyrazolide was developed. The best reaction condition of using lipase PS-D in anhydrousn-hexane at 55 °C was first selected, leading to high yield and enantiomeric excess for the remained (S)-enantiomer. The kinetic analysis by considering the competitive inhibition from butanol was then carried out for obtaining the stereoselectivity ofE1 = 11.2 for the first desymmetrization and enantiomeric ratio ofE3E2−1=11.8 for the subsequent kinetic resolution. The thermodynamic analysis furthermore revealed that the enzyme stereodiscrimination was enthalpy-driven for the desymmetrization step, but changed as entropy-driven for the kinetic resolution step. [ABSTRACT FROM PUBLISHER]

Stereoselective synthesis of the ent-ZA'B'C'D'-ring system of maitotoxin has been accomplished through a convergent strategy utilizing Suzuki-Miyaura cross coupling reaction of ZA'-ring alkylborane and C'D'-ring (Z)-vinyl iodide, and subsequent construction of the B'-ring by reduction of the O,S-acetal. [ABSTRACT FROM AUTHOR]

Since 1965, the stereoselectivity in azoalkane denitrogenation has attracted much attention in both synthetic organic chemistry and physical organic chemistry. In this paper, a short review of the recent findings on the mechanism underlying the fascinating stereoselectivity in azoalkane denitrogenation is presented. The two types of singlet diradicals, i.e. the puckered and planar conformations, were found to play important roles in the stereoselectivity in the photochemical denitrogenation of cyclic azoalkanes. The presence of the puckered singlet diradical, which is the third isomer in homolysis, resolves the mechanistic puzzle reported so far for the stereoselectivity in azoalkane denitrogenations. [ABSTRACT FROM AUTHOR]

A highly efficient lipase AK-catalyzed direct kinetic resolution of a variety of α-allenic alcohols was developed. With the complementary to previous studies, the current reaction system is effective on a broad range of substituents (R 1 ) at C(1), such as alkyl, aryl, alkenyl, and alkynyl groups. The Jones–Burgess empirical model was modified to interpret the reversed selectivity during the acetylation of secondary alcohol. The methyl group at C(2) of allenic alcohols implied a small structural adjustment in the catalytic triad of lipase AK, representing a potential direction for future site-directed mutagenesis. [ABSTRACT FROM AUTHOR]

A diene-transmissive hetero-Diels-Alder reaction of cross-conjugated 1-azatrienes (-1-azadendralenes) is described for the synthesis of hexahydroquinazolin-2-ones and hexahydrobenzothiazine-2-imines derivatives. [4+2] Cycloaddition reactions with tosyl isocyanate or aryl isothiocyanates gave mono-cycloadducts with high chemo- and regioselectivities. The second Diels-Alder reaction with representative dienophiles, tetracyanoethylene, N-phenylmaleimide, and methyl vinyl ketone, stereoselectively produced ring-fused nitrogen heterocycles. Skeletal diversity can be accessed by combining the three reaction partners - primary amine, tosyl isocyanate, and cross-conjugated 1-oxatriene - in a different sequential order. [ABSTRACT FROM AUTHOR]

Fluoride-catalyzed nucleophilic addition of a difluoro(phenylsulfanyl)methyl group ('PhSCF2') generated from PhSCF2SiMe3 to nitrones was accomplished in satisfactory yields. High diastereoselectivities were observed with chiral polyoxygenated cyclic nitrones to provide the corresponding adducts, which were further manipulated to afford gem-difluoromethylenated polyhydroxypyrrolizidines and -indolizidines. [ABSTRACT FROM AUTHOR]

The stereoselective synthesis of the C(31)-C(39) and C(20)-C(27) fragments of phorboxazole A ( 1) was achieved from commercially available and inexpensive D-mannitol. Crimmins aldol reaction and a decarboxylative Claisen-type reaction are the key steps for the C(31)-C(39) fragment, and L-proline-catalyzed aldol reaction, Sharpless asymmetric epoxidation, and epoxide ring opening reaction with Gilman's reagent are the key steps for the C(20)-C(27) fragment of phorboxazole. [ABSTRACT FROM AUTHOR]

Enantiocontrolled construction of B-E rings of penitrem E was accomplished from 4-iodoindole in 13 steps with an overall yield of 1.7%. Diastereoselective Tf2NH-catalyzed (2+2)-cycloaddition between silyl enol ether and methyl acrylate furnished a tetracyclic product possessing the characteristic cyclobutane ring bearing a hydroxyl group. [ABSTRACT FROM AUTHOR]

The first Cu(I)-catalyzed cross-coupling reaction by hydrogen (H2) removal for the stereoselective synthesis of 3-phosphoindoles is reported. Going beyond the oxidative dehydrogenative coupling reactions reported recently, this reaction completely omits the oxidant and base, producing hydrogen (H2) as the only byproduct. [ABSTRACT FROM AUTHOR]

Whole cells of different yeast species have been widely used for a number of asymmetric transformations. In the present study, the screening of several yeast strains revealed the utility of Debaryomyces etchellsii in acyloin condensation for ( R)-(−)-phenylacetylcarbinol production. Some conditions for the efficient biotransformation of benzaldehyde and minimization in the production of by-products were explored: pH of the reaction medium, use of additives (ethanol or acetonitrile), temperature, time, and substrate concentration and dosing. The optimal conditions found allowed the transformation of up to 10 g/L of the starting material in reactions carried out at high scale. Furthermore, the yeast Kluyveromyces marxianus was seen to be a convenient biocatalyst to carry out the kinetic resolution by the bioreduction of racemic (+/−)-phenylacetylcarbinol, resulting in ( S)-(+)-phenylacetylcarbinol with excellent stereoselectivity. Finally, the ketone reduction of both isolated stereoisomers ( R and S) by D. etchellsii allowed the obtainment of two of the four diastereoisomers of 1-phenyl-1,2-propanediol. All these compounds are key precursors for the production of interesting pharmaceutical and chemical products. [ABSTRACT FROM AUTHOR]

With the aim of achieving surface-mediated enantioselective adsorption, the self-assembly of chiral oligo(p-phenylenevinylene) (OPV3T) with nucleosides is investigated at the liquid/solid interface by means of scanning tunneling microscopy and molecular modeling. OPV3T enantiomers form mirror related hexameric rosette patterns. The DNA nucleoside, thymidine, does not self-assemble into stable adlayers but coadsorbs with OPV3T on the surface, leading to a pattern transformation of OPV3T from rosettes to dimers, and a change in chiral expression as well. Diastereoselective recognition between OPV3T and thymidine enantiomers can be used to resolve thymidine enantiomers at an achiral surface with an OPV3T enantiomer as the resolving agent. The impact of molar ratio and concentration on the self-assembly and chiral resolution is systematically investigated. Because there is no interaction between OPV3T and thymidine in solution, the liquid/solid interface acts as the platform for the chiral resolution of thymidine enantiomers. [ABSTRACT FROM AUTHOR]

A mild and highly stereoselective rhodium(II)-catalyzed cyclopropanation of alkenes, alkynes, and allenes with diacceptor diazo compounds is reported. Using the phosphonate moiety as an efficient trans-directing group, the first catalytic asymmetric route to diacceptor cycloprop(en)ylphosphonates was developed by employing an α-cyano diazophosphonate and Rh2(S-IBAZ)4 as chiral catalyst. The isosteric character of phosphonic and carboxylic acid derivatives allowed the alternative use of an α-cyano diazo ester in the process, leading to α-cyano cycloprop(en)ylcarboxylates in high yields and stereoselectivities. Taking advantage of the particular reactivity of the cyanocarbene intermediates involved in this system, the scope of compatible substrates could be extended to substituted allenes, leading to the development of the first catalytic enantioselective method for the synthesis of diacceptor alkylidenecyclopropanes. [ABSTRACT FROM AUTHOR]

Abstract: Two diastereomeric isoxazolines were synthesized in a stereoselective manner with 6.64–20.36% diastereoisomeric excess. The cycloaddition of N-sugar-maleimide in the presence of MgBr2 afforded isoxazolines with high diasterioselectivities (76–84% de). The 1,3-dipolar cycloaddition reaction was diastereospecific and enantiomerically pure (3R,4S,5S,6S,3aR,6aS)-pyrazolines were obtained from N-sugar-maleimides via 1,3-proton migration. [Copyright &y& Elsevier]

The selective oxyfunctionalization of isolated sp³ C-H bonds in complex molecules represents a formidable challenge in organic chemistry. Here, we describe a rational, systematic strategy to expedite the development of P450 oxidation catalysts with refined regio- and stereoselectivity for the hydroxylation of remote, unactivated C-H sites in a complex scaffold. Using artemisinin as model substrate, we demonstrate how a three-tier strategy involving first-sphere active site mutagenesis, high-throughput P450 fingerprinting, and fingerprint-driven P450 reactivity predictions enabled the rapid evolution of three efficient biocatalysts for the selective hydroxylation of a primary and a secondary C-H site (with both S and R stereoselectivity) in a relevant yet previously inaccessible region of this complex natural product. The evolved P450 variants could be applied to provide direct access to the desired hydroxylated derivatives at preparative scales (0.4 g) and in high isolated yields (>90%), thereby enabling further elaboration of this molecule. As an example, enantiopure C7-fluorinated derivatives of the clinical antimalarial drugs artesunate and artemether, in which a major metabolically sensitive site is protected by means of a C-H to C-F substitution, were afforded via P450-mediated chemoenzymatic synthesis. [ABSTRACT FROM AUTHOR]

Cis- and trans-1,2-dihydrodiol isomers of benzene undergo acid-catalyzed dehydration to form phenol. In principle the isomeric substrates react through a common β-hydroxybenzenium (cyclohexadienyl) carbocation. Notwithstanding, the isomers show a large difference in reactivity, kcis/ktrans = 4500. This difference is reduced to kcis/ktrans = 440 and 50 for the 1,2-dihydrodiols of naphthalene and 9,10-dihydrodiols of phenanthrene, respectively, and to 6.9 for the dihydrodiols of the nonaromatic 7,8-double bond of acenaphthylene. Because the difference in stabilities of cis- and trans-dihydrodiols should be no more than 2-3-fold, these results imply a high cis stereoselectivity for nucleophilic trapping of a β-hydroxyarenium cation by water in the reverse of the carbocation-forming reaction. This is confirmed by studies of the 10-hydroxy-9-phenanthrenium ion generated from aqueous solvolyses of the trans-9,10-bromohydrin derivative of phenanthrene and the monotrichloroacetate ester of the phenanthrene cis-9,10-dihydrodiol. The cis stereoselectivity of forward and reverse reactions is explained by the formation (in the "forward" reaction) of different conformations of carbocation from cis- and trans-dihydrodiol reactants with respectively β-C-H and β-C-OH bonds in pseudoaxial positions with respect to the charge center of the carbocation optimal for hyperconjugation. Formation of different conformations is constrained by departure of the (protonated) OH leaving group from a pseudoaxial position. The difference in stability of the carbocations is suggested to stem (a) from the greater hyperconjugative ability of a C-H than a C-OH bond and (b) from enhanced conjugation arising from the stabilizing influence of an aromatic ring in the no-bond resonance structures representing the hyperconjugation (C6H6OH+ ↔ C6H5OH H+). This is consistent with an earlier suggestion by Mulliken and a demonstration by Schleyer that the benzenium ion is subject to hyperconjugative aromatic stabilization. It is proposed that, in analogy with the terms homoconjugation and homoaromaticity, arenium ions should be considered as "hyperaromatic". [ABSTRACT FROM AUTHOR]

An unprecedented stereoselective organocatalytic one-pot 1,4-/1,6-/1,2-addition sequence between β-dicarbonyl compounds, β-nitroalkenes and 4-nitro-5-styrylisoxazoles sequentially catalyzed by low loading of a squaramide catalyst and an achiral base has been developed. The protocol opens an efficient entry to isoxazole bearing cyclohexanes with six consecutive stereogenic centers including one tetrasubstituted carbon in good yields and excellent diastereo- and enantioselectivities. [ABSTRACT FROM AUTHOR]

The article focuses on a research study in the field of chemistry related to stereoselective chemical reactions based on the catalytic reactions and asymmetric process of cyclohexanes. It mentions the application of stereoselective reactions in the synthetic organic chemistry and the significance of the chiral molecules with contiguous multiple stereocenters in cyclohexanes. It discusses the reaction mechanism of asymmetric tandem reactions.

The author discusses research on organometallic chemistry, with a focus on how a stereoselective Heck reaction formed a ketone group and controlled regiochemistry and stereochemistry. Topics include palladium coupling reactions and their role in chemical synthesis, carbon-carbon double bond additions, and nitrogen-based bidentate ligands. Additional information is presented on replacing aryl halide with diazoarene, optimization of ligand sets, and multidimensional parameter-based optimization protocol.