The chemistry of small ring compounds. Part 35. Oxidation of arylcyclopropanone methyl hemiacetals by cupric ions and by oxygen

Abstract

AbstractPhenylcyclopropanone methyl hemiacetals 1a−c can be smoothly oxidised by a variety of oxidising agents, the nature of which exerts a strong influence on the product distribution. The common key‐intermediate in all these reactions is the ring‐opened phenyl stabilised β‐propionate radical 3 (Schemes 1 and 3). When the oxidation is carried out with cupric nitrate in pyridine the main product is meso‐ and racemic dimethyl 3,4‐diphenyladipate 4.With cupric or ferric chloride in acetonitrile or methanol, the intermediate radicals 3a−c combine with a halogen atom in a ligand transfer reaction and afford methyl 3‐chloro‐3‐phenylpropionates 10a−c. Phenylcyclopropanone methyl hemiacetal la rapidly absorbs oxygen in the presence of a catalytic amount of cupric‐pyridine complex, giving methyl benzoylacetate 15 as the main product. Without this catalyst the absorption of one equivalent of oxygen is very sluggish and affords the methyl 3‐hydroperoxy‐3‐arylpropionate 13a. The hydroperoxide formation is notably slower in benzene than in CCl4 or CHCl3. In these chlorinated solvents, 2‐methyl‐2‐phenylcyclopropanone methyl hemiacetal 1c gives the peroxylactone 5‐methyl‐5‐phenyl‐1,2‐dioxolan‐3‐one 14.