Photocycloaddition reactions of pyrazinopsoralen with simple olefins

Abstract

Direct photolyses of pyrazinopsoralen (PzPs) with excess olefins such as dimethyl fumarate (DMFu), dimethyl maleate (DMMa) and dimethyl ethylidenemalonate (DMEM) gave C-4-photocycloadducts. The photoproducts were determined to be 1:1 C-4-cycloadducts formed through the addition of 4',5'-furan double bond of the excited PzPs to the olefins. The fluorescence of PzPs was quenched by olefins with rate constants on the order of 10(9)-10(10) M-1/s, The appearance of the long-lived fluorescence component implies a singlet exciplex mechanism for the photocycloaddition reaction of PzPs with excess olefins.