Reaction of 2‐dimethylaminomethylene‐1,3‐diones with Dinucleophiles. IV. Synthesis of 5,7‐dihydrothiopyrano[3,4‐c]pyrazol‐4(1H)‐ones, 5H‐Thiopyrano[4,3‐d]isoxazol‐4(7H)‐one and 6H‐Thiopyrano[3,4‐d]pyrimidin‐5(8H)‐ones

Abstract

AbstractThe reaction of 2H‐thiopyran‐3,5(4H,6H)‐dione with N,N‐dimethylformamide dimethyl acetal gave in good yield 4‐dimethylaminomethylene‐2H‐thiopyran‐3,5(4H,6H)dione (II), which afforded 1‐substituted 5,7‐dihydrothiopyrano[3,4‐c]pyrazol‐4(1H)‐ones with aliphatic and aromatic hydrazines, 5H‐thiopyrano[4,3‐d]isoxazol‐4(7H)‐one (IV) with hydroxylamine hydrochloride and 2‐substituted 6H‐thiopyrano[3,4‐d]pyrimidin‐5(8H)‐ones with amidines and guanidines, generally in satisfactory yields. 4‐(t‐Butylhydrazonoformyl)‐2H‐thiopyran‐3,5(4H,6H)‐dione was isolated as an intermediate in the reaction of II with t‐butylhydrazine, whereas formamidine gave with II 4‐iminoformyl‐2H‐thiopyran‐3,5(4H,6H)‐dione as the sole product. The isoxazole IV isomerized easily with sodium methoxide to 3,4,5,6‐tetrahydro‐5,5‐dihydroxy‐3‐oxo‐2H‐thiopyrano‐4‐carbonitrile.