Cyclopropanation by tandem radical [2 + 1] cycloaddition conducted by nickel complexes catalyzed electroreduction

Programming Organic Molecules: Design and Management of Organic Syntheses through Free-Radical Cascade Processes

“…3‐ Exo cyclizations may sometimes be rendered irreversible by stabilizing the product radical. This tactic was used to prepare bicyclo[3.1.0]hexane derivatives 26 in C 5x C 3x sequences starting from bromodienes 25 , initiated electrochemically, but mediated by a nickel complex (Scheme ) 30. It was necessary for R 1 and R 2 to be radical stabilizing groups that also facilitated a rapid electron transfer (ET) reaction and the best yield (66 %) was obtained when R 1 =R 2 =R 3 =Ph and X=O.…”

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

“…Another convenient way to initiate radical reactions is to employ a nickel(i) complex as an electron-transfer mediator. [13] Reports pertaining to electrogenerated nickel(i) species as catalysts for the reductive radical cyclization of various organic halides, [14] bromoacetals possessing electrondeficient olefinic moieties, [15] and 2-haloaryl ethers containing unsaturated side chains [16] have demonstrated that the electrochemical method is an excellent alternative to the use of organometallic reagents. 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-1yl radical which cyclizes intramolecularly to form methylcyclopentane as well as dimeric species arising from coupling of both cyclic and acyclic radicals.…”