Synthesis of α,α-disubstituted α-amino esters: nucleophilic addition to iminium salts generated from amino ketene silyl acetals.

Alkoxycarbonyl iminium species are prepared easily by the oxidation of tetrasubstituted amino ketene silyl acetals, and subsequent nucleophilic addition of Grignard reagents to the iminium salts gives α,α-disubstituted α-amino ester derivatives in moderate to good yields, in which aryl and ethynyl substituents are readily introduced.