γ-Substituted pyrrole-based silyl dienol ethers as α-amino acid enolate equivalents: a versatile entry to racemic α-substituted α-amino acids

Abstract

γ-Substituted siloxypyrrole derivatives 5–7 have been synthesized by direct alkylation of N-(tert-butoxycarbonyl)-2-(tert-butyldimethylsiloxy)pyrrole 1. These underwent subsequent alkylation with alkyl halides or aldehydes to produce γ,γ-disubstituted α,β-unsaturated lactam intermediates in good yields. Oxidative cleavage of the C(3)–C(4) bond within the lactam moiety gave rise to a number of α-substituted α-amino acids. These include racemic α-methylphenylalanine 14, α-benzylphenylalanine 15, α-benzylserine 18 and α-methylthreonine 21.