A convenient, simple and one-pot synthesis of dibenzoxanthenes and tetrahydrobenzoxanthenes by nanotitania-supported sulfonic acid as an efficient and highly reusable nanocatalyst

Abstract

Nanotitania-supported sulfonic acid (n-TSA) as a highly powerful solid acid nanocatalyst has been successfully applied for the rapid and green synthesis of dibenzoxanthenes and tetrahydrobenzoxanthenes via one-pot condensation-cyclization reactions of aldehydes with b-naphthol, on the other hand with b-naphthol and 1,3-cyclic diketones. The ease of preparation and handling of the catalyst, operational simplicity, short reaction time, mild reaction conditions, and environmentally benign conditions are the main advantages of these protocols, which led to high yields of products, 70-96 % for dibenzoxanthenes and 65-98 % for tetrahydrobenzoxanthenes. Furthermore, the catalyst could be recycled after a simple work-up, and reused at least five times without substantial reduction in its catalytic activity, confirming the stability of the covalent bonding of acidic centers.