Photochemistry of 2,3-Dimethyl-2,3-diphenylbutane: C-C Homolysis and Protonation-Induced Side-Chain Fragmentation

Article abstract of DOI:10.1021/j100205a049

In dichloromethane upon 248-nm (or 254-nm) irradiation, 2,3-dimethyl-2,3-diphenylbutane (bicumene) undergoes homolysis of the central C-C bond to yield two α,α-dimethylbenzyl (cumyl) radicals (Φ_hom = 0.18).In 2,2,2-trifluoroethanol (TFE) this reaction is less efficient (Φ_hom < 0.02), but a new process is observed, i.e., biphotonic ionization followed by C-C fragmentation of the resulting radical cation leading to the cumyl radical and the cumyl cation.The latter reacts with TFE to give cumyl trifluoroethyl ether.In the more acidic solvent 1,1,1,3,3,3-hexafluoroisopropyl alcohol, the electronically excited state of bicumene is efficiently protonated by the solvent to yield a cyclohexadienyl-type carbocation which undergoes side-chain fragmentation to produce cumyl cation, which was directly observed by its UV absorption and whose electrophilic reactivity was characterized.Photoprotonation followed by side-chain fragmentation was also observed with β-phenylalkanols which give rise to the aliphatic oxo compounds derived from the β-carbon of the side chain.