Photochemistry of 1-isopropylcycloalkyl aryl ketones: Ring size effects, medium effects, and asymmetric induction

The n = 0, 1, and 2 ketones shown above undergo Yang photocyclization in solution, but only the n = 1 analogues react this way in the solid state. Based on X-ray crystallography, these differences in reactivity are attributed to an unusually large distance for 1,4-hydroxybiradical cyclization in the solid state for the n = 0 and 2 ring systems, which leads to predominant reverse hydrogen transfer (rht). Enantiomeric excesses of up to 99% can be achieved in the case of the n = 1 system through the use of the solid-state ionic chiral auxiliary method of asymmetric synthesis.