Cerium-catalyzed α-hydroxylation reactions of α-cyclopropyl β-dicarbonyl compounds with molecular oxygen

Three alpha-cyclopropyl beta-dicarbonyl compounds have been used as probes for alpha-radicals as electrophilic reaction intermediates in a cerium-catalyzed alpha-hydroxylation reaction with molecular oxygen. Since the cyclopropyl group did not ring-open to products with a butenyl moiety, but was retained in the products, a localized unpaired electron at the alpha position can be excluded during the course of the reaction. The alpha-cyclopropyl-substituted substrates were prepared by aldol or Claisen reactions. Other substrates with alpha-methyl, aisopropyl, and alpha-tert-butyl substituents were prepared and converted under the a-hydroxylation conditions in order to estimate steric influences on the yield of the reaction.