Synthesis of optically active α-sulfinylacetaldehyde

Optically active α-sulfinylacetaldehyde is prepared by formylation of the (R)-methyl p-tolylsulfoxide anion with N-formylpiperidine.     

Efficient synthesis of α-substituted ethylphosphonates via CuH-catalyzed conjugate reduction of terminal alkenylphosphonate

An unprecedented approach toward synthesis of α-substituted ethylphosphonates based on CuH-catalyzed conjugate reduction of vinylphosphonates has been successfully developed. This protocol features mild conditions, broad substrate scope, good functional group compatibility, high overall efficiencies, and easy gram-scale synthesis. The Cu-catalyzed reduction takes place in a highly selective manner on the phosphono substituted CC bond in the case of the reaction of alkenylphosphonates bearing both phosphono and alkyl or aryl substituted alkene moieties. Furthermore, the result of competitive reaction indicates that the Cu-catalyzed conjugate reduction of vinylphosphonate is more challenging and reproducible than the corresponding acrylate’s reaction.     

Expedient synthesis of α-substituted fluoroethenes

A mild and efficient synthesis of 1-aryl-1-fluoroethenes from benzothiazolyl (aryl)fluoromethyl sulfones and paraformaldehyde, under DBU- or Cs(2)CO(3)-mediated conditions at room temperature, is described. A comparable diethyl fluoro(naphthalen-2-yl)methylphosphonate reagent does not react with paraformaldehyde under these mild conditions. The utility of the methodology for synthesis of terminal α-fluoroalkenes bearing electron-withdrawing functionalities is also shown.     

Efficient synthesis of optically active α-quaternary amino acids by highly diastereoselective [2,3]-rearrangement of allylic ammonium ylides

A pincer-like chiral auxiliary strategy for synthesizing various optically active α,α-disubstituted amino acids in high yields with excellent enantioselectivities is described.     

Synthesis of optically active analogs of α-tocopherol based on (S)-(+)-dihydromyrcene

New optically active analogs of α-tocopherol (vitamin E) were synthesized starting from enantiomerically enriched (ee≈50%) (S)-(+)-dihydromyrcene. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1631–1634, September, 2000.     

Practical synthesis of 1′-substituted Tubercidin C-nucleoside analogs

Several 1′-substituted analogs of Tubercidin C-nucleosides were prepared using a highly convergent synthesis. Good to high diastereoselectivity was achieved using a variety of nucleophiles targeting the 1′-position. The source for this stereoselectivity is herein proposed. It is thought to be attributed to a temperature-dependent chelation of the incoming nucleophile to either the 2′- or 3′-benzyloxy ether of the ribose core.     

Cu-catalyzed asymmetric conjugate reduction of β-substituted α,β-unsaturated phosphonates: an efficient synthesis of optically active β-stereogenic alkylphosphonates

A series of chiral alkylphosphonates bearing β-stereogenic center were synthesized in good enantioselectivities (up to 95% ee) via the CuH-catalyzed asymmetric conjugate reduction of β-substituted α,β-unsaturated phosphonates under optimal conditions using Cu(OAc)₂·H₂O as the copper source, (R)-SEGPHOS as the ligand, PMHS as the siloxane, and t-BuOH as the additive.     

Stereoselective synthesis of optically active cyclic α- and β-amino esters through lipase-catalyzed transesterification or interesterification processes

A series of cyclic α- and β-amino esters belonging to a family of indolines and quinolines have been efficiently synthesized to study their behavior in lipase-mediated kinetic resolution reactions. The influence of the fused ring structure to the benzene ring and the position of the ester functionality relative to the amino group have been demonstrated, finding excellent values of enantiodiscrimination in the transesterification reaction of methyl indoline-3-carboxylate with n-butanol catalyzed by Candida antarctica lipase B being observed. On the other hand, low to moderate selectivities have been found when using a wide panel of lipases toward methyl indoline-2-carboxylate or 1,2,3,4-tetrahydroquinoline derivatives in alkoxycarbonylation, transesterification or interesterification reactions.     

Chemoenzymatic synthesis of an α-substituted serine derivative

An asymmetric synthesis of an α-substituted serine derivative was achieved by employing PLE-catalyzed hydrolysis of a prochiral malonate derivative, and the absolute configuration of the hydrolyzed product was unambiguously determined by the X-ray analysis of a camphorsulfonic acid derivative.     

α-phosphoryl sulfoxides. X. A general synthesis of optically active α-chlorovinyl sulfoxides

A general and efficient synthesis of enantiomeric α-chlorovinyl p-tolyl sulfoxides 1 using (+)-(S)_C(S)_S-α-chloro-α-dimethoxyphosphorylmethyl p-tolyl sulfoxide as a key substrate for the Horner-Wittig reaction with carbonyl compounds is described. The ratio of geometrical isomers of 1 was determined and briefly investigated. The X-ray diffraction structures of (Z)-1-chloro-1-p-tolylsulfinyl-2-phenyl-ethene and (Z)-1-chloro-1-p-tolylsulfinyl-2-(2-thienyl)-ethene are reported.     

γ-Amino vinyl sulfoxides in asymmetric synthesis. Synthesis of optically pure α-substituted β-amino nitriles

The synthesis of optically pure (E)- and (Z)-γ-amino vinyl sulfoxides derived from commercially available protected α-amino esters is reported. Hydrocyanation of the double bond with Et₂AlCN is completely stereoselective and provides enantiomerically pure α-substituted β-amino nitriles with complete control of the configuration at the α-carbon being exerted by the sulfinyl group.     

Asymmetric synthesis of α,β-substituted β-aminoalkanamides and stereochemical determination

Highly enantiomerically enriched β-aminoalkanamides 12 and β-phenylaminoalkanamides 13 have been prepared by the addition reaction of α-lithiated 2-alkyl-2-oxazolines 9-Li, derived from optically active oxazolines 9, to N-cumyl nitrones 2. The relative stereochemistry of alkanamides 5 and 6 has been established by 1D-NOESY experiments carried out on the related pyrimidinones 7, whereas the absolute configuration of alkanamides 12 and 13 has been confirmed by an X-ray analysis.     

Synthesis of optically active,unnatural α-substituted glutamic acid derivatives by a chiral calcium-catalyzed 1,4-addition reaction

The first catalytic asymmetric 1,4-addition reactions of azlactones with acrylic esters have been developed. A chiral coordinative calcium catalyst was found to be effective for these reactions, and the desired 1,4-adducts were obtained in good yields and enantioselectivities. The product was converted to the corresponding α-alkylated glutamic acid by acid hydrolysis.     

Synthesis of optically active medium-sized α-aminolactams via ring-closing metathesis

The synthesis of optically active medium-sized α-aminolactams via ring-closing metathesis is described. The amidation of optically active N-Boc-allylglycine derivatives with N-protected alkenylamine, and ring-closing metathesis resulted in the formation of medium-sized α-aminolactams with good yield.     

Simple synthesis and separation of the diastereomers of α-thio analogs of ribo- and deoxyribo- di- and triphosphates

Nucleoside 5′-0-(1-thiodi-) and triphosphates can be obtained in yields of up to 45% directly from the nucleosides. Their diastereomers can be separated by preparative reversed phase chromatography.     

Study of the enantioselectivity of the CAL-B-catalysed transesterification of α-substituted α-propylmethanols and α-substituted benzyl alcohols

A study of the enantioselectivity exhibited by the lipase B from Candida antarctica in the transesterification of different α-substituted α-propylmethanols with vinyl acetate is shown. The best results are obtained when the large-sized (L) substituent of the alcohol is either a phenyl group or more especially a cyclohexyl group, although the reaction rates are lower than when linear or slightly branched groups are present. It is also found that ramification at the β-position of the L substituent has a deleterious effect on both lipase activity and enantioselectivity. Moreover, some α-substituted benzyl alcohols bearing medium-sized (M) substituents larger than an ethyl and smaller than a propyl group are resolved by means of this methodology with moderate-good enantioselectivities (E=46–57) and similar reaction rates.     

Synthesis of optically active α-aminophosphine oxides and enantioselective membrane transport of acids with their participation

Russian Journal of General Chemistry -     

Efficient synthesis of optically active β-hydroxy p-tolylsulfones with very high enantiomeric excess via CBS–oxazaborolidine-catalyzed borane reduction

A simple, efficient synthesis of optically active β-hydroxy p-tolylsulfones with >99% e.e. by employing CBS–oxazaborolidine-catalyzed asymmetric borane reduction of β-keto p-tolylsulfones using N-ethyl-N-iso-propylaniline–borane complex as the borane carrier has been established.