Photochemical Isomerization of (E,Z)-1,5-Bis(9-anthryl)penta-1,4-dien-3-one and its Intramolecular Diels-Alder Adduct

Abstract

Photoexcitation of (E,Z)-1,5-bis(9-anthryl)penta-1,4-dien-3-one (2) leads to 4-(9-anthryl)-4,5-dihydro-5,9b[1′,2′]-benzeno-9bH- benz [e]indene-3(3aH)-one (3) which is formed by an intramolecular Diels -Alder addition. Upon irradiation, (3) undergoes a skeletal rearrangement to give a product (4), rationalized in terms of a stepwise reaction involving diradical intermediates. The molecular structure of (4) has been established by X-ray diffraction, and the stereochemistry of (3) deduced from the results of X-ray diffraction studies of its reduction products (5) and (6).