A new strategy for the synthesis of four individual isomers of β-methylphenylalanine

The application of an allylic strain effect in boron enolates and asymmetric Michael- like addition/electrophilic bromination reactions is reported for the asymmetric synthesis of the individual isomers of unusual constrained amino acids. For β-substituted α-amino acids, all of the final optically pure products were identical to authentic samples, which provided further and unequivocal evidence to confirm the assignments of stereochemical control of the new methods in this report.