The photochemical approach to the functionalization of open-chain and cyclic alkanes .2. Hydrogen abstraction

Chloranil (Chl) has been irradiated in the presence of the alkanes 2,3-dimethylbutane, cyclohexane, norbornane, adamantane in acetonitrile. The primary step is hydrogen abstraction by triplet Chl, k(H) 0.8 to 2x10(6) M(-1)s(-1), as confirmed by the detection of the ChlH(.) radical. Hydrogen abstraction from the alkanes is unselective. The thus formed alkyl radicals undergo different reaction, viz: coupling with ChlH(.) (both C-Q coupling to give hydroquinonemonoethers and C-C coupling to give hydroxydihydrobenzoflurans are observed); addition to ground state Chl to yield ultimately alkoxyphenoxyquinones; oxidation by groud state Chl (this process is fast only with tertiary radicals, and the cations formed in this case are trapped by the solvent MeCN to yield acetamides). Different methods for alkane funtionalization are compared. Copyright (C) 1996 Elsevier Science Ltd