Regioselective synthesis of N1-substituted-4-nitropyrazole-5-carboxylates via the cyclocondensation of ethyl 4-(dimethylamino)-3-nitro-2-oxobut-3-enoate with substituted hydrazines

A simple and expeditious method for the regioselective synthesis of N1-substituted-4-nitropyrazole-5-carboxylates was developed. The method involves cyclocondensation of ethyl 4-(dimethylamino)-3-nitro-2-oxobut-3-enoate with a series of monosubstituted hydrazines to give N1-substituted-4-nitropyrazole-5-carboxylates with excellent regioselectivity and good yields. Solvent effects on regioselectivity of the cyclocondensation were examined.