Photocycloaddition Reaction of 1,2-Bispyrazylethylene to Tetracyanoethylene

摘要

Benzene solution oftrans-1,2-bispyrazylethylene and electron deficient olefin, tetracyanoethylene, as a ヰ-acceptor gave 1,2-bispyrazyl-3,3,4,4-tetracyanocyclobutane, a 2ヰ + 2ヰ cycloaddition product, on irradiation with 350 nm UV light. Fluorescence studies revealed the reaction to proceed through a singlet exciplex. The fluorescence of trans-1,2-bispyrazylethylene was quenched very efficiently by tetracyanoethylene with the quenching constant of 1.6 】 1010M-1s-1 while electron rich olefin, tetramethylethylene, did not quench the fluorescence of bispyrazylethylene.