Base-Promoted Cascade Cyclization/Carboxylation of Hydrazones of Conjugated Ynones with CO2: Synthesis of CF3–Pyrazole-4-carboxylates and Pyrazole-3,4-dicarboxylates

Abstract In this work, we have disclosed that available trifluoromethyl-substituted hydrazones derived from conjugated ynones undergo cyclization, followed by carboxylation with CO2 in the presence of K2CO3. The reaction enables the synthesis of a variety of pyrazole-4-carboxylates bearing a trifluoromethyl group in good yields under ambient conditions without the use of transition-metal catalysts. Furthermore, it was found that CF2Br-substituted ynones react with hydrazine salts in alcohols to afford hydrazones containing an alkoxycarbonyl group; these intermediates can also undergo carboxylation, providing access to pyrazole-3,4-dicarboxylates in good yields.