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
摘要:
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 (SET)-hydrogen atom abstraction processes. A series of ketyl fragmentation probes were used to differentiate the two pathways. A SET process is the dominant pathway when the ketones involved are sterically hindered or when strong electron acceptors are used as the substrates. The observation that EPR-active intermediates can be detected, or that small amounts of radical derived products are formed, demonstrates only that a SET pathway is available but cannot be used to establish the mechanism of the major product-forming reactions.