Application of Nazarov cyclization to access [6-5-6] and [6-5-5]tricyclic core embedded new heterocycles: an easy entry to structures related to Taiwaniaquinoids

A concise and general route to synthesize a new class of [6-5-6] tricyclic core embedded polyheterocycles has been accomplished using diastereoselective Nazarov cyclization with an overall yield of 35-40%. Versatility of this synthetic route has also been demonstrated by accessing a variety of [6-5-5] tricyclic core incorporated polycycles. It was observed that the efficiency of cyclization depends upon the impact of polarization on the reacting systems. Amongst the various Lewis and Brønsted acids screened for cyclization, triflic acid was found to be the most effective catalyst.