Long-chain acyloins and vicinal diketones

Abstract

Several methods for the preparation of long-chain vicinal diketones are examined. The acyloin condensation, followed by oxidation, provides an excellent route to symmetrical compounds but is not satisfactory for unsymmetrical diketones. The latter are prepared (i) from dialkylacetylenes by semihydrogenation, hydroxylation, and oxidation with aqueous N-bromosuccinimide; and (ii) from an α-acetoxy-acid chloride and the sodio-derivative of a bistetrahydropyranyl or dibenzyl alkylmalonate, followed by removal of the protecting group and decarboxylation to give the α-acetoxy-ketone, which is then hydrolysed and oxidised.