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-1H-2,1-benzothiazin-4-(3H)-one 2,2-dioxide (4) gave the O-benzoyl compound, 1-methyl-2,2-dioxido-1H-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-methyl-2,2-dioxido-1H-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-1H-2,1- benzothiazin-3yl)-2-propen-1-one (15). On the other hand, 1-methyl-2,2-dioxido-1H-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-4H,6H-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)-1H-pyrido[2,3-c][1,2]thiazin-4(3H)-one 2,2-dioxide (23) and 1-methyl-1H-thieno[3,2-c][1,2]thiazin-4(3H)-one 2,2-dioxide (8).