The setereoselective preparation ofβ-keto esters using baker's yeast in the presence of rice wine koji

By the addition of rice wine koji,enhancement of the reactivity was observed for the baker's yeast reduction ofβ-keto esters into (S)-β-hydroxy esters with high enantiomeric purity (73-98%).     

Solvent-free,one-pot synthesis of α,β-unsaturated esters in the presence of a C3-symmetric arsine

An efficient synthesis of α, β-unsaturated esters is achieved via a one-pot reaction in the presence of a C₃-symmetric arsine. The key advantages are the short reaction time, simple workup, mild reaction conditions, and high yields.     

Diastereoselective synthesis of trans-trifluoromethyl-β-lactams and α-alkyl-β-trifluoromethyl-β-amino esters

The diastereoselective synthesis of β-lactams was examined from N-tosyl-1-chloro-2,2,2-trifluoroethylamine 3 and various nonactivated aliphatic acid chlorides in the presence of a Brønsted base. The mild reaction conditions allowed to get trifluoromethyl-β-lactams in good yields with high trans-diastereo selectivity. In addition, we also demonstrated that ring-opening of β-lactams easily provided α-alkyl-β-trifluoromethyl-β-amino esters.     

Organocatalytic preparation of simple β-hydroxy and β-amino esters: low catalyst loadings and gram-scale synthesis

A combined amino- and N-heterocyclic carbene (NHC)-catalyzed one-pot reaction sequence for the synthesis of simple enantioenriched β-hydroxy and β-amino esters using commercially available catalysts at low catalyst loadings has been developed. The desired products were obtained in high yield and excellent enantiopurity. The generation of quaternary stereocenters and application in gram-scale synthesis were also realized, with no requirements of inert or anhydrous reaction conditions, thus making this transformation a highly practical protocol.     

Selective reduction of α,β-unsaturated esters in the presence of olefins

Several α,β-unsaturated esters containing also isolated olefins or other functionalities subject to saturation were selectively reduced to the corresponding saturated esters by magnesium in methanol.     

Glyoxylic acid as catalyst： A simple selective synthesis of 1,2-disubstituted benzimidazoles in aqueous media

Glyoxylic acid （5 mol%） performs as a novel highly water-soluble catalyst for the synthesis of 2-aryl-l-arylmethyl-lH- benzimidazoles from a wide range of substituted o-phenylenediamines and various substituted aldehydes in good to excellent isolated yields （85-95%） using water as solvent at ambient temperature. The remarkable advantages offered by this method are easily and inexpensive available catalyst, simple procedure, mild conditions, much faster （20--40 rain） reactions and excellent yields of products.     

Acid-labile δ-ketal-β-hydroxy esters by asymmetric hydrogenation of corresponding δ-ketal-β-keto esters in the presence of CaCO3

A series of acid-labile, optically pure ε-substituted δ-ketal-β-hydroxy esters were obtained by a Ru-SunPhos catalyzed asymmetric hydrogenation of the corresponding ε-substituted δ-ketal-β-keto esters. CaCO(3) played a dual role in the hydrogenation reaction--removing the acid generated during the formation of the catalyst and maintaining the activity of the catalyst.     

Synthesis of polyfunctionalized alkenes and α,β-unsaturated γ-lactams from the reaction of alkyl propiolates and CH-acids such as diethyl acetamidomalonate and ethyl acetamidocyanoacetate in the presence of triphenylphosphine

Dialkyl 1-(Z)-2-(acetylamino)-2-butenedioates, 1,1-diethyl-3-alkyl (E)-(1-acetylamino)-2-propene-1,1,3-tricarboxylate, 5-ethyl-1-methyl (E)-4-(acetylamino)-4-cyano-2-pentenedioate and ethyl 1-acetyl-2-cyano-5-oxo-2,5-dihydro-1H-pyrrole-2-carboxylate were obtained from the three-component reactions between alkyl propiolates and CH-acids such as diethyl acetamidomalonate and ethyl acetamidocyanoacetate in the presence of triphenylphosphine at room temperature in dry dichloromethane. Correspondence: Sakineh Asghari, Chemistry Department, Mazandaran University, P. O. Box 453, Babolsar, Iran.     

The setereoselective preparation of β-keto esters using baker＇s yeast in the presence of rice wine koji

By the addition of rice wine koji, enhancement of the reactivity was observed for the baker＇s yeast reduction of β-keto esters into （S）-β-hydroxy esters with high enantiomeric purity （73-98%）.     

Stereo- and regioselective synthesis of β-amino-β-tetrazolylvinylphosphonates

Addition of 5-substituted tetrazoles to dimethyl [(N,N-diisopropylamino)ethynyl]phosphonate proceeds regio- and stereoselectively to yield (Z)-[2-diisopropylamino-2-(tetrazolyl)vinyl]phosphonic acid dimethyl esters. The Z-configuration of the products was confirmed by ¹Н NMR spectroscopy and single-crystal X-ray diffraction. The reactions occur via nucleophilic attack of tetrazole involving predominantly the N-1 atom of the tetrazole ring.     

Stereoselective synthesis and Lewis acid mediated functionalization of novel 3-methylthio-β-lactams

A proficient etiquette for the stereoselective synthesis of novel 3-methylthio-β-lactams and their Lewis acid mediated functionalization is described. Treatment of 2-methylthioethanoic acid and appropriate imines in the Staudinger reaction leads to the stereocontrolled synthesis of novel trans-3-methylthio-β-lactams in excellent yields. cis-3-Chloro-3-methylthio-β-lactams, obtained from stereoselective chlorination of trans-3-methylthio-β-lactams using N-chlorosuccinimide (NCS) and AIBN, were subjected to Lewis acid (TiCl₄ or SnCl₄) mediated functionalization using various active aromatic, heterocyclic and aliphatic compounds (nucleophiles). This reaction provides an easy access to novel, stereoselective cis-3-monosubstituted-3-methylthio-β-lactams, which further undergo smooth desulfurization with Raney-nickel to afford C-3 cis- and trans-monosubstituted-β-lactams. The cis or trans configuration of the hydrogen/chloro/nucleophile substituent at C-3 was assigned with respect to C4–H.     

Stereoselective cyanation of 4-formyl and 4-imino-β-lactams: application to the synthesis of polyfunctionalized γ-lactams

The stereoselective reaction of 4-oxoazetidine-2-carbaldehydes and their corresponding imines with cyanide-based reagents give β-lactam α-aminonitriles, which are chameleonic building blocks for the controlled synthesis of a variety of new compounds including functionalized γ-lactams, succinimide derivatives, and diamino-lactams derivatives in optically pure form.     

Reductive aldol-type reaction of α,β-unsaturated esters with aldehydes or ketones in the presence of Rh catalyst and Et2Zn

The reaction of RhCl(PPh₃)₃ with Et₂Zn easily generated a rhodium–hydride complex (Rh−H) that added to α,β-unsaturated esters to form rhodium enolate complexes by formal 1,4-reduction. These rhodium enolates gave the corresponding Reformatsky-type reagents through transmetalation, and they reacted with various aldehydes and ketones to give reductive aldol-type products in good to excellent yields.     

Efficient one-pot selective reduction of esters in β-ketoesters using LiHMDS and lithium aluminium hydride

The ester functionality in β-keto esters is selectively reduced in one-pot, first by enolization using LiHMDS and then reduced with lithium aluminium hydride. This method produces β-hydroxyl ketones from the corresponding β-keto esters in high yield.     

The synthesis of (Z)-trisubstituted allylic alcohols by the selective 1,4-hydrogenation of dienol esters: improved synthesis of (-)-β-santalol

(E)-Trisubstituted allylic alcohols are commonly prepared from the corresponding (E)-enals, themselves readily accessible by a simple aldol condensation reaction. We demonstrate that these very same (E)-enals can be converted into (Z)-trisubstituted allylic acetates (and thus alcohols) by a ruthenium-catalyzed 1,4-hydrogenation of the corresponding dienol acetates. This simple solution to a long-lasting problem was applied to an industrially feasible synthesis of (-)-β-santalol.     

Influence of steric parameters on the synthesis of tetramates from α-amino-β-alkoxy-esters and Ph3PCCO

α-Aminoesters react with Ph₃PCCO in a domino addition–Wittig cyclization sequence affording enantiomerically pure tetramates. In the case of β-oxo functionalized α-aminoesters, e.g., esters of serine, threonine or β-hydroxyornithine the yields of this reaction depend heavily on the bulkiness of the β-OR group and on the configuration of β-carbon atom C-3. Smaller residues and 2R/3R-configured aminoesters give better yields. The alkoxycarbonyl group of the ester moiety and the residue on the N-atom are less important. These findings can be accounted for by assuming an early puckered transition state for the intramolecular ring-closing Wittig reaction. The addition of sub-stoichiometric amounts of benzoic acid or N-hydroxysuccinimide (for acid-sensitive compounds) is advantageous in some cases as it accelerates the formation of the intermediate amide ylides.     

Solvent-free multicomponent synthesis of pyranopyrazoles: per-6-amino-β-cyclodextrin as a remarkable catalyst and host

A simple, green and efficient protocol is developed with per-6-amino-β-cyclodextrin (per-6-ABCD) which acts simultaneously as a supramolecular host and as an efficient solid base catalyst for the solvent-free syntheses of various dihydropyrano[2,3-c]pyrazole derivatives involving a four-component reaction. This atom-economical protocol, reported for the first time with ketones also, includes a much milder procedure, does not involve any tedious work-up or purification, avoids hazardous reagents/byproducts and results in near quantitative yields. The catalyst can be reused at least six times without any change in its catalytic activity.     

A novel route for the synthesis of α,β-unsaturated esters,ketones and nitriles using dibutyl telluride

In the presence of dibutyl telluride, α-halo-ester, nitrile, and ketone were found to condense easily with aromatic aldehydes to afford α,β-unsaturated esters, nitriles and ketones in high yields as one-pot reaction. A possible reaction machanism was proposed.