SELECTIVE SOLID-STATE PHOTOREARRANGEMENT THROUGH THE LESS STABLE OF 2 POSSIBLE BIRADICAL INTERMEDIATES

The photochemistry of methyl 2-benzoyl-1,4-dihydro-1,4-ethenonaphthalene-3-carboxylate is completely medium-dependent. In solution, two primary di-pi-methane-type photoproducts are formed. Neither of these products is produced when the photolysis is carried out in the solid state; instead, three new photoproducts are formed. The results are interpreted as being due to reaction through 1,3-biradical intermediates, the more stable of which are preferred in solution whereas the less stable ones are formed in the solid state as a result of topochemical restrictions of molecular motion. X-ray crystallographic evidence in support of these ideas is presented and discussed.