Irradiation of 9, 10-dicyanoanthracene (DCA) or p-chloranil in the presence of E-1- benzylidene-2-phenylcyclopropane (E-5) in CH2Cl2 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 ...