Abstract
The reaction of 2‐chloro‐4‐(methylsulfonyl)benzoyl chloride (5) with 1‐methyl‐1__H__‐2,1‐benzothiazin‐4‐(3__H__)‐one 2,2‐dioxide (4) gave the O‐benzoyl compound, 1‐methyl‐2,2‐dioxido‐1__H__‐2,1‐benzothiazin‐4‐yl 2‐chloro‐4‐(methylsulfonyl)benzoate (6), which rearranged to give the C‐benzoyl isomer, [2‐chloro‐4‐(methylsulfonyl)phenyl] (4‐hydroxy‐1‐mefhyl‐2,2‐dioxido‐1__H__‐2,1‐benzothiazin‐3‐yl)methanone (7). The O‐cinnamoyl compound 13 that resulted from the addition of 2,4‐dichlorocinnamoyl chloride (11) to compound 4 rearranged to give the C‐cinnamoyl compound, 3‐(2,4‐dichlorophenyl)‐1‐(4‐hydroxy‐1‐methyl‐2,2‐dioxido‐1__H__‐2,1‐benzothiazin‐3yl)‐2‐propen‐1‐one (15). On the other hand, 1‐methyl‐2,2‐dioxido‐1__H__‐2,1‐benzothiazin‐4‐yl 3‐phenyl‐2‐propenoate (19) (from cinnamoyl chloride (17) and compound 4) rearranged to give 2,3‐dihydro‐6‐methyl‐2‐phenyl‐4__H__,6__H__‐pyrano[3,2‐c][2,1]benzothiazin‐4‐one 5,5‐dioxide (21), an example of a hitherto unknown ring system. Additional examples of this novel heterocycle were prepared from 1‐methyl‐7‐(trifluoromethyl)‐1__H__‐pyrido[2,3‐c][1,2]thiazin‐4(3__H__)‐one 2,2‐dioxide (23) and 1‐methyl‐1__H__‐thieno[3,2‐c][1,2]thiazin‐4(3__H__)‐one 2,2‐dioxide (8).