Preparation and ring transformation of isomeric β-lactam derivatives of bicyclic 1,3-thiazines

Ketene–imine cycloaddition reactions between cis- and trans-2-aryl-4a,5,6,7,8,8a-hexahydro-4H-3,1-benzothazines and chloroacetyl chloride in the presence of base were investigated. Because of the diastereotopic CN faces of cyclohexane-condensed thiazines, both of the possible Staudinger addition product monochloro-β-lactam stereoisomers were obtained for both the cis and the trans compounds. The novel azetidin-2-ones were transformed into the corresponding 3-ethoxycarbonyl-2-aryl-1,5,5a,6,7,8,9,9a-octahydro-4,1-benzothiazepines with sodium ethoxide in a one-step procedure. Structural and stereochemical analyses of the synthesized compounds were carried out by means of IR and NMR spectroscopy.