On the Mechanism of the Reduction of Some Ketones by Organotin Hydrides.Hydride Transfer, Electro-Transfer-Hydrogen-Atom Abstraction, or Free Radical Addition.

Article abstract of DOI:10.1021/jo00212a030

Three aromatic-aliphatic ketones, cyclopropyl phenyl ketone, α,α,α-trifluoroacetophenone and α-fluoroacetophenone, are reduced by triphenyltin hydride by an initiated homolytic reaction to yield organic stannoxides.The reactivity is is not markedly dependent upon solvent polarity.The unitiated reduction with triphenyltin hydride of the more reactive electronegatively substituted fluorinated alkyl-aromatic ketones show a solvent-dependent reactivity.The reactivity increases as the solvent becomes more polar.Both homolytic and heterolytic processes occur in the more polar solvents.The homol ytic reaction appears to be initiated by an electron-transfer process, and the propagation sequence, likewise, contains an electron-transfer step.It appears that in the propagation step the donor-acceptor ability of the reagents determine whether the homolityc reaction proceeds by a radical addition of a tin to the carbonyl oxygen or whether electron transfer occurs prior to tin-oxygen bond formation.A consideration of the timing of these processes suggests a merged mechanism where the donor-acceptor ability of the reagents determines the extent of electron transfer in or after the transition state.