CYCLO-ADDITION REACTIONS OF STILBENE ELECTRON-POOR ALKENE EXCIPLEXES

The fluorescence of trans-stilbene is quenched by several electron-poor alkenes. Quenching by dimethyl fumarate and fumaronitrile is accompanied by the appearance of exciplex fluorescence in nonpolar solvents. Quenching constants increase with increasing alkene electron affinity, indicating that singlet stilbene acts as an electron donor in exciplex formation. The stilbene-dimethyl fumarate exciplex forms a single cycloadduct, dimethyl μ-truxinate, at low conversions. Evidence is also presented for inefficient addition of cis-stilbene and dimethyl fumarate to form selectively dimethyl neotruxinate. Excitation of the weak ground-state complexes of trans-stilbene with dimethyl fumarate and fumaronitrile results in the same chemical reactions and fluorescence which are observed upon diffusive encounter of singlet trans-stilbene and ground-state alkene. Quenching of stilbene excimer by dimethyl fumarate results in the formation of an oxetane cycloadduct and not the cyclobutane formed from singlet stilbene (monomer) with dimethyl fumarate. © 1979, American Chemical Society. All rights reserved.