Highly Diastereoselective Radical Addition to Oxime Ethers: Asymmetric Synthesis of β-Amino Acids

Abstract

Highly diastereoselective alkyl radical addition to Oppolzer's camphorsultam derivatives of oxime ethers provided a convenient method for preparing the enantiomerically pure α,β-dialkyl-β-amino acids. The phase-transfer-catalyzed alkylation was an excellent method for the selective monoalkylation of the N-(β-oximino)acyl derivative of Oppolzer's sultam, with no detection of dialkylated products. In the presence of BF3·OEt2, the carbon radical addition to the oxime ethers proceeded smoothly to give the α,β-dialkyl-β-amino acid derivatives with excellent diastereoselectivity.