Reaction of 6-Aminouracils with Ketenethioacetals

Reaction of ketenethioacetals [methyl 2-cyano-3, 3-bis (methylthio) acrylate (2), 3, 3-bis-(methylthio)-2-phenylsulfonylacrylonitrile (13)] with 6-aminouracils (1a : R1=R2=Me, 1b : R1=Ph, R2=H) in the presence of potassium carbonate followed by cyclization under reflux in diphenyl ether gave the corresponding 5-amino-6-methoxycarbonyl-7-methylthiopyrido [2, 3-d]-pyrimidine-2, 4 (1H, 3H)-dione derivatives (4a, b). Reaction of other ketenethioacetals [2-cyano-3, 3-bis (methylthio) acrylonitrile (10), dimethyl bis (methylthio) methylenemalonate (18), α-oxo ketenethioacetals (21a-e)] with 1 directly afforded pyrido [2, 3-d] pyrimidine derivatives (11a, b, 20a, b, 23a-e) in good yields. 5-Amino-7-methylthiopyrimido [4, 5-d] pyrimidine-2, 4 (1H, 3H)-dione derivatives (16a-c) were also synthesized from 6-aminouracils (1a, b) and dimethyl cyanoimidodithiocarbonate (15) in a manner similar to that used for the preparation of compound 11a.