Electroreductive cyclisation of unsaturated halides catalysed by nickel macrocyclic complexes

Catalytic reduction of 1-iodooctane by nickel(I) salen electrogenerated at carbon cathodes in dimethylformamide: Effects of added proton donors and a mechanism involving both metal- and ligand-centered one-electron reduction of nickel(II) salen

“…Subsequent investigations of processes catalyzed by nickel(I) tetraazamacrocyclic complexes were carried out by Bakac, Espenson, and Ram [6][7][8][9][10]14,15], and Stolzenberg and co-workers probed nickel(I) hydroporphyrin-catalyzed reductions of alkyl halides [11][12][13]17,20]. A number of interesting reductive cyclizations of halogenated compounds promoted by electrogenerated nickel(I) species have been reported by Ozaki and co-workers [16,19,22,23,[25][26][27][28] and by Duñ ach et al [24,[29][30][31]33,35,[37][38][39][40]. Additional papers have appeared from the laboratories of Helvenston and Castro [18], Fry and Fry [21], Esteves and co-workers [32], and Gennaro and Isse [34,36].…”

Electroreductive Radical Cyclization of Ethyl 2‐Bromo‐3‐allyloxy‐ and‐3‐(propargyloxy)propanoates Catalyzed by (Tetramethylcyclam)nickel(I) Electrogenerated at Carbon Cathodes in Dimethylformamide

“…Reductive intramolecular cyclization of 6-iodo-and 6-bromo-1-phenyl-1-hexyne, catalyzed by electrogenerated (salen)nickel(i), affords benzylidenecyclopentane in 84-95 % yield; [17] (salen)nickel(i)-catalyzed reduction of 6-bromo-1-hexene involves homolytic scission of the carbon-bromine bond to give the 5-hexen-1-yl radical which cyclizes intramolecularly to form methylcyclopentane as well as dimeric species arising from coupling of both cyclic and acyclic radicals. [18] In other investi-gations, [19][20][21] it was reported that electrogenerated nickel(i) complexes catalyze the reduction of unsaturated halides to yield alkenyl radicals, which react intramolecularly to give carbocyclic products. Finally, the use of nickel(i) complexes as mediators for radical cyclization has been applied to the synthesis of substituted tetrahydrofurans, for which the furofuran moiety is an important subunit in a wide range of biologically active natural products.…”

Nickel Mediated Radical Reactions

“…ii : BER (2.5 equiv) -Ni2B (0.075 equiv), Nal (7.5 equiv) DMF has been demonstrated to give methylcyclopentane in 46% yield [22]. This clearly suggests that this nickel-catalyzed electroreductive cyclization proceeds via a radical pathway.…”