ChemInform Abstract: Synthesis of 4‐Aryl‐4,6‐dihydropyrimido[4,5‐d]pyridazine‐2,5(1H,3H)‐diones from Biginelli Compounds.

Abstract

Biginelli compounds 1 were first brominated at MeC(6) with 2,4,4,6-tetrabromocyclohex-2,5-dien-1-one to give Br2CHC(6) derivatives 2. The hydrolysis of the 6-(dibromomethyl) group of 2c to give the 6-formyl derivative 3c in the presence of an expensive Ag salt followed by reaction with N2H4⋅H2O yielded tetrahydropyrimido[4,5-d]pyridazine-2,5(1H,3H)-dione (4c; Scheme 1). However, treatment of the 6-(dibromomethyl) derivatives 2 directly with N2H4⋅H2O led to the fused heterocycles 4 in better overall yield (Schemes 1 and 2; Table).