Allenyl(vinyl)methane photochemistry. Photochemistry of γ-allenyl-substituted α,β-unsaturated enone derivatives

The photolyses of the γ-allenyl-substituted alkylidenecycloalkanones underwent mainly E–Z geometric isomerization; several enones gave pyrans by the photochemical intramolecular oxa-Diels–Alder reaction and bicyclo[2.1.0]pentanes by the intramolecular [2+2] cycloaddition. The photolyses of the γ-(3-methyl-1,2-butadienyl)-substituted 3-alkylidenepenta-2,4-diones led to bicyclo[2.1.0]pentane, while the γ-(1,2-propadienyl-substituted) 3-alkylidenepenta-2,4-diones underwent intramolecular [2+2] cycloaddition and intramolecular oxa-Diels–Alder reaction.