Diastereoselective formation of cage-type adducts via a novel photoreaction of nicotinic acid esters with furan

Irradiation of a benzene solution containing 2-alkoxynicotinic acid esters (0.02 M) and furan (0.2 M) resulted in the formation of cage-type adducts in 73–84% yield. The structure of the adducts was established by X-ray crystallographic analysis. The mechanism involving 4π+4π photocycloaddition between the pyridine ring and furan was postulated. Two diastereomeric 4π+4π adducts were detected as intermediates in the 1H NMR spectroscopy, when the solution was irradiated in the presence of diene as a triplet quencher.