Intramolecular photocycloaddition of 4-phenoxybut-1-enes: a convenient access to the 4-oxatricyclo[7.2.0.0]undeca-2,10-diene skeleton

Abstract

The photochemistry of 4-phenoxybut-1-ene is markedly influenced by the presence and position of electron-withdrawing substituents on the benzene ring. A cyano substituent in the 2′- or 4′-position promotes an efficient intramolecular cycloaddition to give good yields of the 4-oxatricyclo-[7.2.0.0]undeca-2,l0-dienes, by way of the photolabile 11-oxabicyclo[6.3.0]undeca-1,3,5-triene, the precursor of which is presumed to be a thermally labile intramolecular ortho photocycloadduct. The 3′-cyano isomer reacts inefficiently and only the 2′-isomer in the methoxycarbonyl series undergoes the photocycloaddition. The formation of the trienes is efficiently quenched by 1,3-dienes but their intramolecular cyclisation is unaffected by the presence of the triplet quenchers.