The Aryl Version of the Cyclopropyl-?-Methane Rearrangement. Partitioning of a 1,4-Diradical: Mechanistic and Exploratory Organic Photochemistry

Article abstract of DOI:10.1021/jo00249a030

The photochemistry of 2-(2,2-diphenylcyclopropyl)-2-phenylpropane (8) was investigated in a search for the arylcyclopropylmethane counterpart of the known vinylcyclopropylmethane reaction.Direct irradiation of arylcyclopropylmethane 8 led to 1,1-diphenylethylene (3) and 1-phenyl-2-methyl-1-propene (13) as products in addition to the usual Griffin fragmentation leading to diphenylcarbene (15) and 3-methyl-3-phenyl-1-butene (7). 1,1,3-Triphenyl-2,2-dimethylcyclobutane (12) was considered as a potential reaction intermediate.The cyclobutane was synthesized and found to afford alkenes 3 and 13 on irradiation.However, dynamic isotope dilution revealed that only 1percent of the reaction did proceed via this intermediate, and its presence was eventually detected by FT NMR.The triplet of arylcyclopropane 8 proved unreactive.A third mechanism involving a Griffin fragmentation was considered and ruled out by independent generation of the carbene and observation of the products.Quantum yields were obtained.Also excited singlet-state lifetimes and reaction rates were determined by using single photon counting.The electronic features leading to the observed reactivities are discussed.