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

Abstract

+ catalytically reduces these two compounds at potentials significantly more positive than those required for direct reduction of the bromo

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

“…In addition, the values of I c /I d obtained in media containing water, i.e. in microemulsions and in ethanol/water mixtures [17] are larger than those obtained in the previous investigation in organic solvents [15,16]. Thus, the polarity of the medium may play a role in the specific catalytic activity.…”

“…The preparative scale controlled-potential electrolysis for 1b and 1c at RVC took place for only a short time before the cell current decayed to background level, and only a small amount of bromoester was consumed. In a previous investigation of the catalytic reductions of those bromoesters with electrogenerated nickel(II) complexes [16] similar rapid current decay was observed at platinum electrode and this was attributed to the formation of a passivating film on the surface of the cathode. Hence, to overcome this problem, the catalytic reduction of 1b and 1c was carried out using carbon felt cathodes instead of RVC.…”

“…Identities of the major products (2 and 3) derived from controlled-potential electrolyses were confirmed by comparison of gas chromatographic retention times as well as 1 H NMR and mass spectra for the isolated products with those of the authentic compounds [15,16].…”

“…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

“…Other investigations have entailed the use of electrogenerated nickel(I) salen in an ionic liquid [51] as well as the stoichiometric reaction between an alkyl halide and nickel(I) salen (in the presence of dioxygen, water, and light) to afford an aldehyde [54,56] or ketone [60]. In addition, some electrogenerated tetraazamacrocyclic complexes have been employed for the catalytic reduction of ethylene halohydrins [49] and bromo esters of propargylic and allylic ethers [53,58]. Finally, electrogenerated [2,2 0 -([2,2 0 -bipyridine]-6,6 0 -diyl)bis[phenolato]-N,N 0 ,O,O 0 ]nickelate(I) is a catalyst for the reductive cleavage of 1-iodooctane [55], and nickel(II) salen has been discovered recently [59] to undergo alkylation of the ligand imino bonds during the catalytic reduction of a primary alkyl halide.…”