α,β-Unsaturated Carboxylic Acid Derivatives. VIII. The Synthesis and Reaction of Esters N-Acyl-N-bromo-α-dehydroamino Acid

The addition of bromine to t-butyl 2-(N-acylamino)-2-alkenoate (3) was accompanied by the elimination of hydrogen bromide and the decomposition of the ester group to give 2-(N-acylamino)-3-bromo-2-alkenoic acid, while the bromination of 3 with NBS gave the corresponding N-bromo derivative (7), whose bromine atom gradually migrates to give t-butyl 2-(N-acylamino)-3-bromo-2-alkenoate. The substitution of the bromine of 7 with nucleophiles gave, successively, the corresponding N-methoxy, N-benzyloxy and N-cyano derivatives, while that with sodium azide gave the corresponding migration products. The structures of the new compounds were assigned.