Cycloaddition reactions of 1.3-benzothiazines v synthesis of new tetracyclic ring systems

New tetracyclic derivatives (3a,b, 5, 8) similar to protoberberines, but containing a lactam structural element and other hetero atoms besides the bridge-head nitrogen in rings B and C, were prepared by cycloaddition of 6,7-dimethoxy-2H-1,3-benzothiazine (1a) with o-substituted aromatic carboxylic acid derivatives (2a,b, 4) and from 4- methyl-6,7-dimethoxy-2H-1,3-benzothiazine (1b) with 3.5-dinitrobenzoyl chloride.