The study of indirect electroreductive cyclization of propargyl derivatives using [Ni(tmc)]Br₂ as catalyst in ionic liquids

Radical cyclization continues to be a central methodology for the preparation of natural products containing heterocyclic rings. The use of electrogenerated nickel(I) complexes as mediators for cathodic intramolecular cyclizations proved to be successful in the formation of carbocyclic products. In this work, the indirect electroreductive intramolecular cyclization of bromoalkoxylated derivatives 1 catalyzed by electrogenerated (1,4,8,11-tetramethyl-1,4,8,11-tetraaza-cyclotetradecane)nickel(I), [Ni(tmc)]⁺, as the catalysts in the ionic liquids, N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide, [N_{1 1 1 2(OH)}][NTf₂] and 1-ethyl-3-methylimidazolium ethylsulfate, [C₂mim][C₂SO₄] has been investigated by cyclic voltammetry and controlled-potential electrolysis. During controlled-potential electrolyses of solutions of Ni(II) complex in the presence of bromoalkoxylated derivatives 1, only five-membered-ring esters were obtained in moderate to good yields as the main products.