USE OF A SACRIFICIAL ALUMINUM ANODE IN THE ACYLATION OF SOME OLEFINS

The acylation of some alicyclic and aliphatic alkenes by the electroch emical generation of a catalyst using a sacrificial aluminum anode was investigated. Substrates were electrolyzed in a dichloromethane solut ion of an appropriate electrolyte (tetraalkylammonium salts) in the pr esence of an acylating agent (acetyl chloride or anhydride). Thus, uns ubstituted cycloalkenes, namely cyclohexene and cycloheptene, gave by that reaction conjugated ketones, i.e. the corresponding 1-acetylcyclo alkenes, as the only unsaturated carbonyl compounds in moderate-to-goo d yields. Under the same reaction conditions their 1-methyl derivative s gave mixtures of the corresponding conjugated and beta, gamma-unsatu rated isomeric ketones in which unconjugated compounds predominate. In both cases unsaturated ketones were accompanied by different amounts of side products. Terminal aliphatic alkenes (1-hexene, 1-heptene, and 1-dodecene) afforded only conjugated a ketone with a normal skeleton, but in lower yields. The acylation of cyclohexene was studied in more detail, altering the reaction conditions by changing the reaction tem perature, the supporting electrolyte, the acylating agent and the elec trochemical cell. Mechanistic considerations were made on the basis of the products distribution and some theoretical calculations being mad e by the MOPAC program package (version 7.0).