Keten SS-acetals. Part 9. Reaction of α-oxo- and α-cyano-keten SS-acetals with cyanoacetamide: a new general method for substituted and fused 4-alkylthio-3-cyano-2(1H)-pyridones and formation of novel pyridones through base-induced rearrangements

Abstract

α-Oxoketen SS-acetals (1a-n) react smoothly with cyanoacetamide (2) in the presence of sodium isopropoxide in refluxing propan-2-ol to give 4-alkylthio-3-cyano-2(1H)-pyridones (3a-n), respectively, in good to excellent yields. α-Cyanoacetals (4a-c), however, yielded corresponding 6-aminopyridones (5a-c) in relatively lower yields. Extension of this method to cyclic keten SS-acetals (6a-c) and (8a-c) similarly afforded good yields of fused pyridones (7a-c), benzoquinolone derivatives (9a and b), and the benzocycloheptane derivative (9c), respectively. Attempts to isolate 4-alkoxypyridones (12a and b) under varying conditions were not successful. Reaction of α-alkyl-α-oxoketen SS-acetals (15a-g) and (21a-c) with cyanoacetamide under similar conditions afforded novel pyridones (16a-g) and (22a-c) respectively, which are formed by initial base-induced proton migration in these acetals.