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2.2.4.3 Methyl Radical Addition to Styrenes

DOI: 10.1055/sos-SD-213-00070

Ballini, R.; Petrini, M.Science of Synthesis: C-1 Building Blocks in Organic Synthesis, (20142143.

The homolytic cleavage of the C—N bond in nitroalkanes is the basis of the well-known radical denitration process which allows reduction of nitroalkanes to the parent alkane derivative as well as their involvement in C—C bond formation. Nitromethane is seldom involved in these processes because of the poor stabilization of the corresponding methyl radical. A palladium-catalyzed oxidation of styrenes 31 to the corresponding 1,2-dioxo derivatives 32 in the presence of molecular oxygen is proposed to proceed via a methyl radical intermediate (Scheme 13).[‌27‌] The utilization of 2,2′-azobisisobutyronitrile greatly enhances the efficiency of the process, which also requires the presence of an inorganic base. A preliminary regioselective addition of the methyl radical to the double bond is followed by the oxidation of the benzylic position. A further oxidation of the resulting aryl ketone readily provides the target compound. An isotopic labeling study using 18O2 has clearly demonstrated the exclusive involvement of molecular oxygen in the oxidation steps.

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