Divergent oxidative rearrangements in solution and in a zeolite: Distal vs proximal bond cleavage of methylenecyclopropanes

Irradiation of 9,10-dicyanoanthracene (DCA) or p-chloranil in the presence of E-1-benzylidene-2-phenylcyclopropane (E-5) in CH₂CI₂ causes E-5 to undergo methylenecyclopropane rearrangement. An adduct, Z-7, between DCA and 5 firmly supports the involvement of a bifunctional trimethylenemethane radical cation. In contrast, incorporation of E-5 into HZSM-5 produces trans,trans-1,4-diphenyl-1,3-butadiene radical cation sequestered in the HZSM-5 interior, tt-8^·+ @ HZSM-5, identified by ESR and diffuse reflectance spectroscopy. In addition, low yields of tt-8, its cis, trans-isomer (ct-8), and 1-phenyl-1,2-dihydronaphthalene (9) were isolated from the supernatant solution. The sharp contrast between the photoinduced electrontransfer reaction with photosensitizers in solution and the spontaneous reaction with redox-active acidic zeolite offers the prospect of further zeolite-induced regiodivergent reactions in a range of additional substrates.