THE USE OF CHEMICAL PROBES TO DIFFERENTIATE BETWEEN POLAR AND SET HYDROGEN-ATOM ABSTRACTION PATHWAYS INVOLVED IN THE REDUCTION REACTION PROMOTED BY AN 8-AL-4 ANION

The mechanism for the reduction of aromatic ketones and alkyl halides with lithium tetrakis(N-dihydropyridyl)aluminate was found to proceed competitively by hydride reduction and by single electron transfer (SE T)-hydrogen atom abstraction processes. A series of ketyl fragmentatio n probes were used to differentiate the two pathways. A SET process is the dominant pathway when the ketones involved are sterically hindere d or when strong electron acceptors are used as the substrates. The ob servation that EPR-active intermediates can be detected, or that small amounts of radical derived products are formed, demonstrates only tha t a SET pathway is available but cannot be used to establish the mecha nism of the major product-forming reactions.