Novel heterocycles. Synthesis of 2,3‐dihydro‐6‐methyl‐2‐phenyl‐4 H ,6 H ‐pyrano[3,2‐c][2,1]benzothiazin‐4‐one 5,5‐dioxide and related compounds

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 ).