A New Synthetic Approach to Indazole Synthesis

Stobbe condensation of 3-alkyl- or aryl-4-formylpyrazoles 3a-f with diethyl succinate in the presence of potassium t-butoxide, followed by intramolecular ring closure (Ac2O-NaOAc), afforded the corresponding indazole derivatives 5a-f in 65-85% overall yield. These compounds are good starting materials for transformation to biologically active molecules, such as new pyrazole analogs of the left-hand segment of the potent natural antineoplastic agent CC-1065.