Electrogenerated Nickel(I) complexes as catalysts for the intramolecular radical cyclisation of unsaturated α-bromoesters

Electrosynthesis of nitrogen heterocycles using environmentally friendly methodologies

“…Formal electrode potential is -0.86 V vs an Ag / AgCl / 3M KCl in water reference electrode. Therefore, from these results we can conclude that the reduction of the [Ni(tmc)]Br 2 complex is a oneelectron reversible process, which is in agreement with the results obtained in previous investigations in DMF [15][16][17][18][19]. The data from these experiments are presented in Table 3.…”

“…A number of useful studies on the construction of lactams by radical cyclisation have been performed and the success of the reaction has been shown to depend strongly on the nature of the substituents on both the -position of the amide and the nitrogen which would affect the stability of both the initially generated radical and the cyclised intermediate [5][6][7][8][9]. On the other hand, substantial efforts have been made to develop a more convenient alternative method and the electrochemical radicaltype cyclisations have been successfully used with unsaturated organic halides [10][11][12], bromoacetals [13], 2-haloaryl ethers [14], bromo propargyloxy esters, bromo allyloxy esters [15][16][17][18] and bromopropargyl ethers [19]. These reactions use Ni(II) complexes as electrontransfer catalysts able to generate Ni(I) derivatives and the corresponding radicals of the organic halides, which afford the cyclisation products.…”

Organic cyclisations of propargyl and allyl bromoesters in microemulsions catalysed by electrogenerated nickel(I) tetramethylcyclam

“…There is, however, substantial evidence in the literature that catalytic reductions of alkyl halides by electrogenerated nickel(I) complexes occurs via an inner-sphere mechanism giving rise to an alkyl-nickel intermediate which further evolution may generate alkyl radicals [26,[12][13][14][15][16][17][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. Moreover, all the products obtained in the microemulsions are consistent with radical intermediates.…”

“…We have been interested in the electrosynthesis of cyclic organic molecules mediated by square planar nickel complexes, in particular the reactions [12][13][14][15][16] …”

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].…”