Benzyl radicals combination pathways

For samples photolyzed on ZSM-5 zeolite, the product distributions of 31 and 32 are dramatically different from those photolyzed in homogeneous solutions. First, the rearrangement products were totally suppressed. Second, diphenylethane 39 resulted from coupling of benzyl radical was not found. Only phenol 38 and toluene were detected. In contrast, photolyses of 33 and 34 on ZSM-5 follow strikingly different pathways. Both photo-Fries rearrangement 36 and 37 and decarbonylation products 35 and 39 were formed. These results can be understood from consideration of size- and shape-selective sorption combined with restriction on the mobility of the substrates and reaction intermediates imposed by the pentasil pore system. 

The combination of an aryl- or alkylsulfonamide, 3 equiv. PhI(OAc)2 and substoichiometric I2 is able to promote C-H animation of simple hydrocarbons in the absence of any metal catalyst [120]. These reactions are best performed neat (10-fold excess of substrate relative to RS02NH2) at 50°C and appear to operate with reasonable selectivity to give benzylic sulfonamide products. Over-oxidation to the sulfonylimine is noted in some cases. A proposed reaction mechanism posits the intermediacy of a sulfonamidyl radical, formed from the AModosulfonamide. This pathway parallels in many ways the mechanism invoked for the Hofmann-Loffler-Freytag process. 

Another strategy involves decomposition of a peroxide or other initiator in the presence of a monomer. Conditions can be chosen such that only one unit of monomer is consumed. I hus, decomposition of UBPOX in S in the presence of DTBN provides 101 (Scheme 9.20). " The monomer initiator and/or combination should be chosen with care to obtain high yield of effective alkoxyamines. Many oxygen-centered radicals react with monomer by multiple pathways. Specificities shown by oxygen-centered radicals in their reaction with monomers have been studied extensively and are discussed in Section 3.4.2. Hydrogen abstraction, often by a source of f-butoxy radicals at low temperature [e.g. (/BuO)2/hv, DBPOX, " /BuOOH/Co(lI) "- j, in the presence of a nitroxide is another common method for generating benzylic and other alkoxyamines. 

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