Photochemistry in a box. Photochemical reactions of molecules entrapped in crystal lattices: mechanistic and exploratory organic photochemistry

Abstract

An exploration was made of the photochemical behavior in the crystalline state of a series of molecules we have previously studied in solution. The reactions studied fall into the categories of cyclohexenone rearrangements, reactions of di-{pi}-methane systems, and the behavior of a molecule giving a long-range phenyl migration in solution. The 4,4-diaryl-cyclohexenones differed from the solution behavior in giving the trans-bicyclic photoproducts without the cis isomers and the 3,4-diarylcyclohexenones. In the case of 4,5,5-triphenylcyclohexenone, the bicyclic photoproduct had inverted stereochemistry compared with solution and otherwise showed entirely different photochemistry than the usual solution cyclobutanone formation. The di-{pi}-methane systems gave rise to three types of behavior: (1) An intramolecular 2{sub {pi}} + 2{sub {pi}} cycloaddition between a dicyanovinyl and a phenyl group, (2) di-{pi}-methane reactivity but with reversed regioselectivity, and (3) cyclopentene formation where the reactant has an additional vinyl group on the methane carbon. Finally, 1,1,5,5-tetraphenyl-3,3-dimethyl-1-penten-5-ol afforded five- and six-membered ring ethers rather that the solution phenyl migration. Solid-state quantum yields were determined with use of a newly designed apparatus. Several quantitative approaches for correlating solid-state reactivity to molecular geometry and crystalline constraints were devised.