The electroreduction of methyl decanoate (1) by using alkali metal ion-free BU4NClO4 as a supporting electrolyte and platinum as anode and cathode was carried out in the presence of several kinds of alkali metal ion sources. The use of BU4NClO4 as a supporting electrolyte without alkali metal ions gave only a trace amount of the reduced product. The addition of 0.05 equiv. of LiClO4 or NaClO4 into this electroreduction system gave the reduction product, 2-alkoxytetrahydrofurans 5 in ca. 20% yield. In this electrolysis, the ligand effect of the alkali metal ion sources was remarkably noted, that is, the electroreduction using sodium ion-crown ether complexes, especially, sodium ion-the polymeric crown ether ligands such as poly(vinylbenzo-15-crown-5-co -styrene) complex, greatly increased the efficiency of the electroreduction. It is plausible that alkali metal (0) species are electrogenerated from alkali metal ions and react as active reductants to reduce the aliphatic esters and the mediatory system is established in this electrolysis system. (C) 2003 Elsevier Science Ltd. All rights reserved.