Substituent effects on the acid-catalyzed isomerization of 2-cyclohepta-2,4,6-trienyltropone derivatives to 2-benzyltropones

Abstract

The acid-catalyzed isomerization of the cycloheptatriene ring of 2-cyclohepta-2,4,6-trienyltropones to give benzyltropones via the norcaradiene intermediate has been studied. In the cases of 7-substituted 2-cyclohepta-2,4,6-trienyltropones (1a–f), the first-order reaction rate is dependent on the nature of the substituent on C-7 of the tropone nucleus, and an electron-withdrawing substituent could accelerate the rearrangement. On the other hand, 2-cyclohepta-2,4,6-trienyltropones (2a–c), (3a–c), and (4b, d), each of which has a substituent on the cycloheptatriene ring, exhibited remarkable chemoselectivity of C–C bond cleavage of the norcaradiene intermediate. The first-order reaction rate is dependent on both the electronic nature and the position of the substituents.