Boron Photochemistry : XII. The role of iodine in the photocyclization of anilinodimesitylboranes

The ratio of methyl group rearrangement to methyl group elimination during the photocyclization of anilinodimesitylborane is dependent upon the concentration of iodine present. At iodine concentrations of less than 10^?3M, the major product is a demethylated borazarophenanthrene, 7,9-dimethyl-6-mesityldibenzce]1,2]-azaborine (IV). At concentrations of iodine above 5 × 10^?3M, the major products is a methyl-rearranged borazarophenanthrene, 7,9,10-trimethyl-6mesityldibenzce]1,2]-azaborine (V). The role of iodine was at least threefold: assisting in the production of a reactive cation-radical at low iodine concentrations, quenching the formation of the cation-radical at higher iodine concentrations, and actively assisting at the higher concentrations in the formation of a reactive species.