Reaction of methyl N-Boc-N-phenoxycarbonylglycinate with various aldehydes afforded the corresponding cis-4, 5-oxazolidinone derivatives, which were effectively converted to (E)-α, β-didehydroamino acids by means of a base. Furthermore, N-deprotection of the oxazolidinone derivatives and subsequent coupling reaction with Boc-amino acid furnished the corresponding dipeptides, which were transformed to dipeptide containing α, β- ...
