Photochemical Studies on Bicyclo[2.1.1]hexyl Derivatives:Chemical Behavior and Asymmetric Induction

The photochemical behavior of bicyclo[2.1.1]hexyl derivatives was investigated by irradiation with a 450 W medium-pressure mercury lamp in acetonitrile solution.The irradiation of methyl bicyclo[2.1.1]hexane-5-carbonylbenzoate(1a)led to both Norrish type II cyclization and cleavage products with a molar ratio of 1∶2.2,whereas the irradiation of methyl 5-methylbicyclo[2.1.1]hexane-5-carbonylbenzoate(1b)afforded the only Norrish/Yang photocyclization compound as the sole product.Such results were illustrated by several geometric parameters for Norrish/Yang photoreaction asφ_(1),φ_(4) andβobtained from the crystal structures.Furthermore,asymmetric pho-tochemical studies using ionic chiral auxiliary technique were also conducted in the solid state.