INTRAMOLECULAR ORTHO AND META PHOTOCYCLOADDITIONS OF 3-ALKYL-4-PHENOXYBUT-1-ENES

Upon irradiation of 3-alkyl-4-phenoxybut-1-enes 1a-d at 254 nm in cycl ohexane, ortho and meta photocycloadditions occur. The ortho photocycl oadducts rearrange readily, while the meta photocycloaddition involves the 2',6'-positions of the arene as directed by the alkoxy group. In each case only a single meta photocycloadduct with an endo alkyl group is formed resulting in six contiguous stereocentres. A 3-alkyl group does not influence significantly the mode selectivity.