Abstract Trimethylsilylamines, Me 3 Si-NR 2, react with N-Cbz-L-serine-β-lactone in acetonitrile primarily by alkyl oxygen cleavage of the lactone ring to give optically pure N- Cbz-β-amino-L-alanine derivatives in good yields. Use of halogenated solvents such as chloroform alters the regiospecificity to give primarily acyl oxygen cleavage and generate amides of N-Cbz-L-serine. The latter are also obtained by reaction of aluminum-amine ...