Investigation of ring transformations of diaryl-β-lactams condensed with 1,3-benzothiazines

Reactions of derivatives of the isoquinoline analog trans-2,2a-diaryl-2,2a-dihydro-5,6-dimethoxy-1H,8H-azeto[2,1-b][1,3]benzothiazin-1-one were studied under basic conditions. Their treatment with sodium methoxide in methanol resulted first in alcoholysis of the beta-lactam ring, followed by opening of the thiazine ring and oxidation of the thiol moiety to disulfide. Thus, the corresponding beta-amino acid derivatives, disulfides of N-(ortho-mercaptobenzyl)substituted diaryl-3-aminoacrylic acid methyl esters, were obtained in good yields. The structures of the new molecules were proved by means of NMR and IR spectroscopy. Geometric isomerism investigations indicated the presence of the Z forms of the acrylic acid moiety.