Radical addition to oxime ethers for asymmetric synthesis of β-amino acid derivatives

The diastereoselective alkyl radical addition to chiral oxime ethers was studied with a view to preparing enantiomerically pure alpha,beta-dialkyl-beta-amino acid derivatives. The phase transfer-catalyzed alkylation of Oppolzer's camphorsultam derivative of oxime ether proceeded smoothly to give the alkylated N-(beta-oximino)acyl derivatives. In the presence of BF3.OEt2, radical addition to the oxime ethers proceeded using triethylborane as the radical initiator to give alpha,beta-dialkyl-beta-amino acid derivatives with excellent diastereoselectivity.