Facile synthesis of pyrazoles and pyrroles via thermolysis of tetrazolo[1,5-b]pyridazines, tetrazolo[1,5-a]pyrimidines and tetrazolo[1,5-a]pyridines

A simple and high yielding preparation of pyrazoles and pyrroles is describ ed. Thermolysis of tetrazolo[1,5-b]pyridazines, tetrazolo[1,5-a]pyrimidines and tetrazolo[1,5-a]pyridines allowed easy ring contraction thus providing a facile preparation of cyanopyrazole and cyanopyrrole heterocycles. Since the cyano group is a versatile precursor of other functionalities, the rea ction appears of particular interest for the construction of a variety of p yrazoles and pyrroles. The simple preparation of the starting tetrazole der ivatives, the relatively mild conditions employed, and the very short react ion times make this versatile procedure of great synthetic utility and appl icable both to small and large scale preparation. (C) 2000 Elsevier Science Ltd. All rights reserved.