Synthesis of higher α-chlorovinyl and α-bromovinyl amino acids: The amino protecting group determines the reaction course

Article abstract of DOI:10.1016/0040-4039(96)00832-5

N-Trifluoroacetyl α-vinyl amino esters are smoothly converted to the corresponding α-chlorovinyl or α-bromovinyl amino esters through the agency of phenyselenyl chloride or phenylselenyl bromide, respectively, followed by oxidation and pyrolysis. Exclusively the (E)-external halovinyl isomer and the internal halovinyl isomer are observed. The amino protecting group is a critical determinant of the reaction course (alkene addition vs. 5-exo-trig- like cyclization).