Asymmetric Syntheses of Derivatives of beta- and gamma-Aryl and alpha-Alkyl Amino Acids Using n-BuLi/(-)-Sparteine

Synthesis of Exclusively 4-Substituted β-Lactams through the Kinugasa Reaction Utilizing Calcium Carbide

A new Kinugasa reaction protocol has been elaborated for the one-pot synthesis of 4-substituted β-lactams utilizing calcium carbide and nitrone derivatives. Calcium carbide is thereby activated by TBAF·3H₂O in the presence of CuCl/NMI. The ease of synthesis and use of inexpensive chemicals provides rapid access of practical quantities of β-lactams exclusively substituted at position 4.

Studies of Azetidin-2-one as a Reactive Enolate Synthon of β-Alanine for Condensations with Aldehydes and Ketones

Studies describe formation of the lithium enolate of N-(4-methoxybenzyloxy)azetidin-2-one (1) and characterization of representative aldol reactions with aldehydes and ketones. Diastereoselectivity features the production of anti-aldol adducts from α,β-unsaturated ketones and α-branched aliphatic aldehydes. The stereoselectivity is rationalized via closed, six-membered transition-state arrangements leading to the formation of Felkin-Anh and anti-Felkin products. Examples illustrate the direct incorporation of monocyclic β-lactams into a variety of molecular architectures. The utility of 1 as an enolate synthon of homoglycine (β-alanine) is illustrated by the efficient synthesis of novel β-amino acid derivatives, including complex 4-hydroxy-2-pyridinones.

Synthesis of chiral lactams via asymmetric hydrogenation of α,β-unsaturated nitriles

A highly efficient Rh-catalyzed asymmetric hydrogenation of α,β-unsaturated nitriles containing ester/amide groups is reported affording chiral nitriles with excellent enantioselectivities (up to 99.7% ee) and high activity (TON up to 10 000).

Highly efficient asymmetric hydrogenation of cyano-substituted acrylate esters for synthesis of chiral γ-lactams and amino acids

A highly efficient Rh-catalyzed asymmetric hydrogenation of 3-cyano acrylate esters is reported for the first time, which provides straightforward access to chiral cyano compounds with excellent enantioselectivities (up to 98% ee) and high turnover numbers (TON up to 10 000).

Direct and diastereoselective alkylation and aldol reactions of α-bromo-α-fluoro-β-lactams

Herein, we describe the development of a method for the direct alkylation and aldol reaction of α-bromo-α-fluoro-β-lactams. This method provides facile access to a wide range of 3-alkyl- and 3-hydroxyalkyl-fluoro-β-lactams in good yields under mild conditions. The products were obtained with complete diastereoselectivity with regard to the relative configuration of the β-lactam ring at C3 and C4 positions. The reaction conditions were tolerant of a broad range of electrophiles, which highlights the overall scope and utility of this procedure.

An Unusual β-Vinyl Effect Leading to High Efficiency and Enantioselectivity of the Amidase, Nitrile Biotransformations for the Preparation of Enantiopure 3-Arylpent-4-enoic Acids and Amides and Their Applications in Synthesis

Biotransformations of 3-arylpent-4-enenitriles catalyzed by Rhodococcus erythropolis AJ270, a nitrile hydratase/amidase-containing microbial whole-cell catalyst were studied, and an unusual beta-vinyl effect of the substrate on the biocatalytic efficiency and enantioselectivity of the amidase was observed. While 3-arylpent-4-enenitriles and 3-phenylpentanenitrile were efficiently hydrated by the action of the less R-enantioselective nitrile hydratase, the amidase showed greater activity and higher enantioselectivity against 3-arylpent-4-enoic acid amides than 3-arylpentanoic acid amides. Under very mild conditions, nitrile biotransformations provided an efficient synthesis of highly enantiopure (R)-3-arylpent-4-enoic acids and (S)-3-arylpent-4-enoic acid amides, and their applications were demonstrated by the synthesis of chiral gamma-amino acid, 2-pyrrolidinone, and 2-azepinone derivatives.

Asymmetric Lithiation−Substitution Sequences of Substituted Allylamines

[reaction: see text] (-)-Sparteine-mediated asymmetric lithiation-substitution sequences of 2- and 3-substituted N-(Boc)-N-(p-methoxyphenyl) allylic amines with electrophiles have been investigated. Asymmetric lithiation-substitutions of N-(Boc)-N-(p-methoxyphenyl) allylic amines 11, 12, 13, 14, and 15 provide highly enantioenriched enecarbamates in good yields. Further transformations to give aldehydes, acids, ketones, and a Diels-Alder adduct are reported. The 1,4-addition products from reactions of the lithiated allylic amines from 14 and 15 with conjugated activated alkenes gives enecarbamates with two and three stereogenic centers in good yields with high diastereomeric and enantiomeric ratios. Synthetic transformation of these products by acid hydrolysis and subsequent cyclization provide stereoselective access to bicyclic compounds containing four and five stereogenic centers with high diastereoselectivity and enantioselectivity. It is suggested that allyllithium complexes generated by asymmetric deprotonation react with most electrophiles with inversion of configuration.

Synthesis of Highly Enantioenriched All-Carbon Quaternary Centers: Conjugate Additions of Chiral Organolithium Nucleophiles to α,α-Dinitrile β,β-Disubstituted Olefins

[reaction: see text]. Highly enantioenriched quaternary centers are obtained by the reaction of chiral lithiated intermediates complexed to (-)-sparteine with tetrasubstituted, alpha,alpha-dinitrile activated olefins. Lithiated N-Boc-N-Aryl benzylamine furnishes products with drs from 78:22 to 95:5, with ers exceeding 94:6. Lithiated N-Boc-N-Aryl allylamine reactants provide enecarbamate products with drs from 55:45 to 99:1, with ers ranging from 87:13 to 97:3.