Synthesis and photochemistry of 4,4-diphenyl- γ-pyran. Di-π-methane rearrangement in a new chromophore

Abstract

A synthesis of 4,4-diphenyl-γ-pyran (1) was elaborated from diphenylmethane. Prolonged irradiation of pyran 1 in tert-butyl alcohol led to: trans-endo-5,6-diphenyl-2-oxabicyclo[3.1.0]-hexene (18), isomeric 3,5-diphenylpenta-2,4-dienals (6), trans-tert-butyl 3,5-diphenylpent-2-enoate (7), cis-tert-butyl 3,5-diphenylpent-2-enoate (8), and isomeric 3,5-diphenylpent-2-enoic acids (9). It was established that the photolysis of γ-pyran 1 yields only one primary photoproduct: the oxabicyclo[3.1.0]hexene derivative 18 via a di-π-methane rearrangement. The other compounds isolated result from further irradiation of the primary product. The results observed are discussed in the light of the di-π-methane rearrangement mechanism.