Steric effects on [4+4]-photocycloaddition reactions between complementary anthracene derivatives

The steric effect of peripheral functional groups on the [4+4]-photocycloaddition between substituted anthracene derivatives was examined. The reactivity of 2,3,6,7-tetraphenylanthracene (TPA) with 2-phenylanthracene (PA), 2,9,10-trimethylanthracene (TMA) and 9,10-dimethyl-2,3-diphenylanthracene (DMDPA) was investigated. In all cases, the photodimers were formed in high yield despite the steric bulk of the peripheral substituents. It was further shown that although PA is capable of forming its homodimer, it selectively reacts with TPA when the latter is excited at 301 nm.