ИСТИНА

Single electron transfer (SET) as an initial stage is a fundamental and fruitful concept for many polar reactions. Chain radical-nucleophilic processes play an important role in nucleophilic aromatic substitution (SRN1) as well as in various transformations of organotransition metal complexes. Metal carbonyl anions are good one-electron donors, but up to now there were no clear-cut examples of SET reactivity with these anions in vinylic or aromatic substitution reactions. The 3-halocyclohexen-2-one system turned out to be unique in providing the possibility to observe the transition from polar addition-elimination reactivity to SET-mediated pathways in the reactions with carbonylmetallates. This mechanistic switch can be triggered by visible light or by steric hindrance introduced by 5,5-dimethyl substitution in cyclohexenone. In case of pentacarbonylrhenate anion SET initiates a radical-chain process leading to products of formal oxidative addition (Scheme). With iodide the reaction pathway is further shifted to halogenophilic process.