von Richter Cinnoline Synthesis

Abstract

The preparation of cinnoline derivatives involving the diazotization of 3‐( o ‐aminoaryl) propiolic acids or o‐ aminoarylacetylenes, and subsequently intramolecular cyclization of resulting diazonium intermediate in the presence of a halide or hydroxide is known as the von Richter cinnoline synthesis. The study suggests that the temperature is the main factor, which decomposes the o ‐ethynylphenyltriazene and favors the formation of cinnoline, whereas a relatively low temperature and the presence of CuCl will lead to the formation of isoindazole. This reaction generally requires substituents at 4‐ and often 3‐positions, which can be removed only under harsh conditions when extra R groups exist on the benzene portion. This reaction is still the major reaction for the preparation of cinnoline derivatives.