Synthesis of spirodienone derivatives and their conversion into dihydrobenzopyrans

The spirodienones 5, 6, and 12–14 including optically active ones were synthesized by anodic oxidation of the corresponding phenol derivatives. Although the asymmetric centers included in the substrates had little effect on the diastereomeric selectivity of the cyclization, the asymmetric structure of the products led to a regioselective conversion into dihydrobenzopyrans 16, 17, and 21–26 under mild Lewis acid-promoted conditions.