RING-EXPANSION REACTION OF 1-HYDROPEROXY-16-OXABICYCLO[10.4.0]HEXADECANE CATALYZED BY COPPER IONS - USE IN THE SYNTHESIS OF 15-PENTADECANOLIDE

A catalytic procedure has been developed for the synthesis of 15-penta decanolide (1) from readily available 1-hydroperoxy-16-oxabicyclo[10.4 .0]hexadecane (2). The method is based on the reaction of hydroperoxid e 2 with copper acetate (0.15-5 mol.%). Ring expansion occurred as a r esult of generation of tertiary bicyclohexadecyloxyl radicals 4 from h ydroperoxide 2 under the action of Cu-I ions, beta-scission of the rad icals accompanied by regioselective cleavage of the bridge bond to for m macrocyclic C-centered radicals 5, and their oxidation by Cu-II ions to (E)-11- and (E)-12-pentadecen-15-olides (6). The products obtained were converted into 15-pentadecanolide by subsequent catalytic hydrog enation over a Pd catalyst in a yield of more than 90% with respect to hydroperoxide 2.