SYNTHESIS AND PHOTOREACTION OF ALPHA-METHYLENE-GAMMA-BUTYROLACTONE-PSORALEN HETERODIMERS

Three double-headed molecules were synthesized by linking a photoreact ive linear (1, 2) or angular (3) furocoumarin via a linear 10- or 5-ca rbon chain to an electrophilic alpha-methylene-gamma-butyrolactone. Th e photochemical behavior of these molecules was investigated in ethano l at 365 nm and the photocycloadducts obtained from each compound were isolated and characterized, In all cases, the photoreactivity results showed the 3,4-pyrone double bond of the psoralen (linear or angular) to be the most reactive and [2 + 2] intramolecular photocycloadducts between the 3,4-pyrone and the exomethylenic double bonds were obtaine d, With compounds 1 and 2, two kinds of intramolecular photocycloadduc ts were obtained, namely cis-syn-exo derivatives in 46% and 36% yield, respectively, and trans-syn-exo derivatives in 14% and 18% yield, res pectively, With compound 3, only the trans-syn-exo derivative was obta ined in 33% yield.