One-Pot Regioselective Synthesis of Pyrazole-5-Carboxylates

Significance

The first example of a regioselective one-pot synthesis of pyrazole-5-carboxylates from the cyclization of hydrazone dianions with diethyl oxalate is reported. Although, in general, the reaction was effected in moderate to good yields, it proceeded poorly when oxalyl chloride or ethyl 2-chloro-oxoacetate, or a tosyl-protected hydrazone were used as reagents. X-ray crystallographic analysis of one of the cyclization products was obtained. Bi- and tricyclic pyrazole carboxylates have also been prepared by this method.