PRODUCTS FROM PHOTOCHEMICAL-REACTIONS AND ELECTROCHEMICAL OXIDATION OF METHYLENECYCLOPROPANE

The reactivity of methylenecyclopropane (MCP, 1) and its radical catio n (1(+.)) have been studied in the presence and absence of a nucleophi le (methanol). Photochemical reactions of 1 in the presence of an elec tron-acceptor (1,4-dicyanobenzene, 6) and a codonor (biphenyl, 7) in a cetonitrile (with and without methanol present) or chloroform lead to cycloadditions (ortho, meta, and para; products 12-17) rather than pro ducts from photoinduced electron transfer (PET). Based on the measured (cyclic voltammetry, CV) oxidation potential, using the Weller equati on, electron transfer (ET) was predicted to occur. It was shown that t he measured oxidation potential of 1 represents the adiabatic ionizati on potential. For PET processes the value for the vertical ionization potential must be used. Electrochemical (EC) generation of 1(+.) witho ut a nucleophile present results in the formation of one major product : tert-butyl acetamide (25). A series of rearrangements leading to the tert-butyl cation is proposed. Addition of a nucleophile (methanol) t o the mixture leads to the formation of 3-methoxy-2-(methoxymethyl)-1- propene (26). This product may arise from trapping of the initially fo rmed ring-opened (trimethylenemethane) radical cation (1a(+.)), which undergoes a second oxidation and nucleophilic addition (ECE).