Photocyclization of a naphthyl substituted Y-enyne

Y-enyne 1 undergoes electrocyclic ring closure, via a cumulene intermediate 2, to photoproduct 3 upon irradiation at 350 nm in the presence/absence of air. In non-polar solvents, a [1,5] H-shift affords the photoproduct. In MeOX (X=H/D), protonation/deuteration of the central allenic carbon in 2 occurs. The X-ray structure of 3, the photoproduct upon irradiation of 1 in benzene, is reported.