An unexpected isomerization of 1,3-benzothiazine and isoquinoline-condensed β-lactams

A series of novel aryl-substituted β-lactams condensed with 1,3-benzothiazines, isoquinolines or 1,4-benzothiazepine were obtained by means of the Staudinger reaction and isomerized in the presence of sodium methoxide to the thermodynamically more stable form. The structures of the new molecules were determined by NMR spectroscopy. Theoretical calculations corroborate the experimentally observed structure–reactivity relationships.