Nickel-Catalyzed Electroreductive Radical Reactions

Electroreductive addition reactions of organic halides to carbon-carbon double or triple bonds have been investigated since early 1980. Nickel compounds have also been used as radical generators in electroreductive processes [21], More recently, the indirect electroreduction of 6-bromo-l-hexene with [Ni(cyclam)] +(C104 )2 (66) in 

DMF has been demonstrated to give methylcyclopentane in 46 M) yield [22]. This clearly suggests that this nickel-catalyzed electroreductive cyclization proceeds via a radical pathway. [Ni(cyclam)] +(CI04 )2 (66), [Ni (CR)] (C104 )2 (67) or [Ni (tet a)] (C104 )2 (68) have been used as efficient catalysts in DMF in the presence of NH4CIO4 as a proton source [23 24]. Ni species generated electro- 

Thus indirect electroreduction of haloethers 69 and 71 led to the corresponding cyclized tetrahydrofuran derivatives 70 and 72, respectively, in good yields via 5-exo-trig mode [23], On the other hand, A -allyl-a-bromoamide 73 gave the corresponding pyrrolidone 74 in DMF in the presence of 2 equiv of a hydrogen donor, diphenylphosphine, whereas A -allyl-cx-iodoamide 75 gave the iodinated pyrrolidone 76 in acetonitrile [24], 

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