RING CONTRACTION IN THE PHOTOCHEMISTRY OF 1,2-DIHYDRONAPHTHALENE OXIDE

The photochemistry of 1,2-dihydronaphthalene oxide was studied in orde r to determine the pathway by which rearrangement to ring-contracted p roducts occurs. The amounts of indan were found to be the same in both acetonitrile and 1,4-dioxane which suggests that the process is dirad ical and not ionic. The substituted oxirane, 4,4-dimethyl-1,2-dihydron aphthalene oxide, was photolyzed in order to distinguish between a Gro b-type fragmentation pathway and a simple 1,2-alkyl shift and it was f ound that indan ultimately originates from a 1,2-alkyl shift to form 1 -formylindan followed by decarbonylation. It was also found that, alth ough indan is not a primary photoproduct, it is formed very early in t he reaction mixture, whereas the concentration of its precursor 1-form ylindan remains low. Both sensitization and quenching experiments have shown that this is not a result of a bimolecular radical reaction, bu t rather due to the starting material sensitizing the initially formed aldehyde.