Tetrahydronaphthalene as a precursor of new series of chalcones, flavanones, and flavones

An efficient synthetic route for a novel series of chalcones 2a–2d as well as for the corresponding flavanones 3a–3d and flavones 4a–4d, using functionalized tetrahydronaphthalene (THN), is described herein. The Claisen–Schmidt condensation of such THN and aromatic aldehydes, in the presence of an aqueous solution of KOH (40%), selectively gives the expected chalcones 2a–2d, which may further undergo an intramolecular oxa-Michael addition using piperidine, affording the corresponding flavanones 3a–3d in high yields. Alternatively, treatment of such chalcones 2a–2d with I 2 /DMSO provides rapidly, in a one-pot oxidative cyclization, a series of flavones 4a–4d in excellent yields ranging from 85% to 90%.