THE PUTATIVE ROLE OF HOMOCONJUGATION IN RADICAL CATIONS - ELECTRON TRANSFER PHOTOCHEMISTRY OF 7-METHYLENENORBORNADIENE AND 7-METHYLENEQUADRICYCLANE

摘要

Photoinduced electron transfer from 7-methylenenorbornadiene, MN, and 7-methylenequadricyclane, MQ, to an excited sensitizer/acceptor in the presence of methanol generates products of several structure types. All products require nucleophilic capture of the radical cations, MN(.+) and MQ(.+), by methanol, followed by rapid rearrangements of the resulting free radicals to C-. as the key intermediate. The short lifetime of the primary products of capture is ascribed to the allylic nature of their C-4-C-5 bonds. The stereochemistry of the methoxy groups in the products indicates that the nucleophile attacks MQ(.+) exclusively from the ''exo'' face (''backside'' attack), whereas MN(.+) shows, in addition, a limited degree of attack from the ''endo'' face. [References: 56]