Intramolecular Meta Photocycloaddition of Conformationally Restrained 5-Phenylpent-1-enes. Part I: Bichromophoric Cyclohexane Derivatives

Article abstract of DOI:10.1016/0040-4020(95)00373-G

The cis isomers of 1-allyl-2-phenycyclohexane and 1-benzyl-2-vinylcyclohexane yield predominantly 1,3 addition, while the trans isomers show a high selectivity for 2,6 addition, which is explained by steric interactions.Introduction of a third substituent, OH or OCH3, on the alkenyl substituted carbon of the cyclohexane ring gives almost exclusively 1,3 addition.This can mostly be explained in terms of more steric hindrance in the conformations leading to 2,6 addition.From the results described it can be concluded that for 2,6 additon two conformations are available, while the energy difference between the 1,3 conformations is much larger and therefore a completely stereoselective 1,3 addition is found (except for 6).