Ethylation of aliphatic ketones on electroreduction in tetraethylammonium fluoroborate–liquid ammonia solutions

Abstract

The reduction of acetylcyclopropane and pentan-2-one by electrogenerated solvated electrons in liquid ammonia in the presence of butyltrimethylammonium fluoroborate, or several other tetra-alkylammonium salts, gives the same products as when lithium metal is used as the source of solvated electrons, but when the electroreduction is performed in the presence of tetraethylammonium fluoroborate the major products are tertiary alcohols, R¹R²C(OH)Et. Tributylethylammonium fluoroborate also functions as an ethylating agent, but not as a butylating agent. These results are rationalised on the basis of the stability of Et₄N⁺ and Bu₃EtN⁺ towards solvated electrons, and the instability of the other tetra-alkylammonium cations under these conditions.