The Photochemistry of Bis(2,2-diphenylvinyl) Ether: A Search for the 3-Oxa-di-?-methane Rearrangement

Article abstract of DOI:10.1021/jo00224a050

A convenient synthesis for bis(2,2-diphenylvinyl) ether (1a) from diglycolic acid via dehydration of 2,2'-oxybis(1,1-diphenylethanol) (3a) is described.The solution photochemistry of divinyl ether 1a derives from its singlet ?,?^*-state and parallels that of the unsubstituted divinyl ether (1d) and that of furan in the gas phase.Formation of a singlet D_?,? vinyl-vinyloxy radical pair is the primary photoreaction (Φ_-S = 0.12-0.19).All photoproducts can be convincingly rationalized from this initial radical pair.For example, cage recombination affords 2,2,4,4-tetraphenyl-3-butenal (13) as the main product.The mechanistic interpretations are based on results from product studies, photo-CIDNP and crossover experiments.The triplet excited state of divinyl ether 1a was found to be inert toward decomposition. trans,trans-Bis(2-phenylvinyl) ether (1c) could be prepared from trans,trans-1,4-diphenyl-1,3-butadiene via epoxidation of its Diels-Alder adduct with bis(2,2,2-trichloroethyl)azodicarboxylate and thermal denitrogenation of the corresponding azo compound.The divinyl ether 1c readily cis-trans isomerizes upon triplet sensitization, thus implicating cis-trans isomerization as the deactivation mode of triplet divinyl ether 1a. 3-Oxa-di-?-methane reactivity of divinyl ether 1a could not be observed.This result is interpreted in terms of Zimmerman's formalism of bond-order control.Irradiation of the authentic vinyloxirane 7 resulted in the photoextrusion of diphenylcarbene affording 3,3-diphenylpropenal.The intermediacy of the corresponding carbonyl ylide 14 was established by low-temperature UV spectroscopy.