Photocyclization of a conjugated triaryl 'Y-enyne'

Upon irradiation at 350 nm, in the presence/absence of oxygen, 'Y-enyne' 1 undergoes electrocyclic ring closure to photoproduct 4. A mechanism involvi ng an allene intermediate is proposed. In nonpolar solvents a [1,5] H shift affords the photoproduct, while in methanol protonation of the central all enic carbon occurs. Quantum yields of the photoreaction in the different so lvents were measured. (C) 2001 Published by Elsevier Science Ltd.