Amino Acids as Electrode Modifiers in the Diastereoselective Electropinacolization of 4-Fluoroacetophenone

One of the most well-known cathodic reactions is the reduction of ketones to yield the corresponding alcohol or the dimerization product (pinacol). The electropinacolization is a very convenient way to form new C–C bonds, which could also feature diastereo- and enantioselectivity. Amino acids have often been used to induce chirality in reactions involving carbonyl compounds. Thus, amino acids could, in principle, affect both diastereo- and enantioselectivity by interaction with the carbonyl group or with the reduction intermediates. In particular, chiral amino acids were used to functionalize the electrode surface, either by directly electrografting them or by electrografting carbon nanoparticles covalently linked with them. Moreover, in order to intercept solution processes, also, the dissolution of amino acids in the catholyte was considered. Using chiral amino acids, we were able to unexpectedly obtain exclusively the pinacol, instead of the alcohol, from the cathodic reduction of 4-fluoroacetophenone in high yield (up to 93%) and high diastereomeric ratio (up to 85/15 dl/meso), despite there being no enantioselection.