Ring transformation and cyclization reactions of 1,1-dioxo-1,2-thiazines -Syntheses of pyridines and benzo[c]thiazines with new substitution pattern

In presence of ammonia/ammonium acetate the 3,5-dimethyl-2-phenyl-1, 1-diox o-1,2-thiazine-4-carbaldehyde (1) reacts with ethyl cyanoacetate to the eth yl 2-cyano-4-[1-methyl-2-methylthio-2-(N-phenylsulfamoyl)vinyl)hexa-2,4-die noate (3) and the Knoevenagel condensation product 4-(2-ethoxycarbonyl-2-cy anovinyl)-3,5-dimethyl-6-methylthio-1,1-dioxo-2-phenyl-2H-1,2-thiazine (2a) . The 4-(2,2-dicyanovinyl)-3,5-dimethyl-6-methylthio-1, 1-dioxo-2-phenyl-2H -1,2-thiazine (2b) is obtained from 1 and malononitril. The masked 1,5-dica rbonyl compound 2a undergoes rind transformation to the 3-cyano-1,6-dimethy l-5-[1-methylthio-2-(N-phenylsulfamoyl)vinyl] pyridin-2-one (5) with methyl amine. With ethanolic ethoxide the condensation products 2a,b afford the 7- amino-6-ethoxycarbonyl-4-methylthio-2,2-dioxo-1-phenyl-benzo[c]1,2-thiazine (6a), respectively the corresponding 6-cyano derivative 6b, while 3 cycliz ises to furnish ethyl 2-amino-6-methyl-5-[1-methyl-2-methylthio-2-(N-phenyl -sulfamoyl)vinyl] nicotinate (4).