Salicylanilide esterification: unexpected formation of novel seven-membered rings

Novel benzoxazepines were prepared upon esterification of biologically active salicylanilides with some N-protected amino acids. While the desired conjugates of the salicylanilides with the amino acids were obtained when sterically more demanding amino acids were used, benzoxazepines were formed as a result of a seven-exo-trig cyclization in the case of N-protected glycine and alanine. The structures of the products were confirmed by 2D NMR methods, and further transformations of the acyclic conjugates provided additional support for the proposed mechanism of cyclization.