Electrochemical Reduction and Intramolecular Cyclization of 6-Iodo-1-phenyl-1-hexyne at Vitreous Carbon Cathodes in Dimethylformamide

Article abstract of DOI:10.1021/jo00296a021

In dimethylformamide containing a tetraalkylammonium perchlorate, a cyclic voltammogram for reduction of 6-iodo-1-phenyl-1-hexyne at a glassy carbon electrode exhibits three prominent waves corresponding to cleavage of the carbon-iodine bond and to subsequent reductions of 1-phenyl-1-hexyne and benzylidenecyclopentane.At potentials for which only reduction of the carbn-iodine bond occurs, large-scale electrolytes of 6-iodo-1-phenyl-1-hexyne afford benzylidenecyclopentanone and 1-phenyl-1-hexyne; the yield of the carbocycle, averaging 36percent, is insensitive to potential, but the quantity of 1-phenyl-1-hexyne varies from 28 to 48percent as the potential is chosen to be more negative.In the presence of diethyl malonate as a proton donor, the quantity of benzylidenecyclopentane changes little, the yield of 1-phenyl-1-hexyne decreases, and substantial (>33percent) diethyl (1-phenyl-1-hexyn-6-yl)malonate is obtained.With 1,1,1,3,3,3-hexafluoroisopropyl alcohol as proton source, the yield of benzylidenecyclopentane increases to approximately 60percent, whereas the quantity of 1-phenyl-1-hexyne decreases somewhat.It appears that each of the major hydrocarbon products is formed via a combination of one- and two-electron processes.