Cyclooctatrienes from pyran-2-ones via a tandem [4 + 4]-photocycloaddition/decarboxylation process

摘要

Irradiation of pyran-2-ones bearing pendent furans in aqueous MeOH followed by heating furnished fused bicyclic products containing a cyclooctatriene ring.rnAppearance of the cyclooctane ring in natural products is surprisingly frequent, given the challenges connected with its direct formation from acyclic precursors in the flask. There has been considerable activity focused on the development of efficient and general methods for the construction of cyclooctanes, especially within a larger polycyclic skeleton. Among these, strategies that form the ring through a cycloaddition process are especially attractive, as they allow retrosynthetic disconnection of two cyclooctane bonds and a corresponding simplification to two smaller precursor fragments. In a fascinating example of such a higher-order cycloaddition, 4,6-di-methylpyran-2-one was shown by de Mayo et al. to undergo a photochemical dimerization to furnish diastereomeric cyclooctadienes with two lactone bridges (Scheme 1). Pyrolysis effected double decarboxylation by retrograde [4 + 2]-cycloaddition to give tetramethylcyclooctatetraene.