A novel synthetic route to 3,4-benzotropolones: the expansion of a six-membered carbocycle under reducing conditions

Abstract

6,7-Dimethyl-3,4-benzotropolone (III; R¹= H, R²= Me) and the related 5-hydroxy-3,4-benzotropolones (III; R¹= OH, R²= Me) and (III; R¹= OH, R²= H) are formed in good yield when derivatives of 2-acetyl-3,4-dihydronaphthalen-1 (2H)-one ate treated with zinc in acetic acid. The reductive ring expansions are discussed in terms of cyclopropanediol intermediates.