Electroreductive intramolecular cyclisation of bromoalkoxylated derivatives catalysed by nickel(I) tetramethylcyclam in “green” media

The (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetra-decane)nickel(I), [Ni(tmc)]+, electrogenerated at glassy carbon cathodes is shown to be an effective catalyst for the intramolecular radical-type cyclisation of bromoalkoxylated derivatives 1 in alcohol and/or alcohol/water mixtures as well as in microemulsions made with cationic and anionic surfactants. The results obtained indicate that the reaction proceeds via cleavage of the carbon–bromine bond to form a radical-type intermediate that undergoes cyclisation on the unsaturated C–C bond to afford substituted tetrahydrofurans. The reactions are more selective and take place at higher current density than when carried out in conventional aprotic solvents.

► Alcohol, alcohol/water mixtures and microemulsions are synthetically useful media. ► Rates of conversion of bromoalkoxylated derivatives are high in microemulsions. ► Electrogenerated [Ni(tmc)]+ seems to be a viable catalytic alternative to Bu3SnH.