One-Step Synthesis of delta-Lactones Having Biological Activity by Remote Carbonylation

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In this work, a novel straightforward method for the synthesis of delta-lactones has been pursued. Taking advantage of the lead tetraacetate-induced oxidation of alcohols, a novel delta-lactone synthesis from saturated alcohols and CO was achieved. This remote carbonylation is quite general for primary and secondary alcohols whose delta-carbons are primary or secondary. In case of an alcohol having both primary and secondary delta-carbons, carbon monoxide is incorporated at the secondary carbon in a 24 : 1 ratio. The reaction sequence can be successfully applied to a one-step synthesis of a carpenter bee sex pheromone starting from commercially available, optically pure (R)-(-)-2-hexanol and carbon monoxide. On the other hand, attempted reaction of a 1,2-diol type substrate resulted in beta-fragmentation rather than carbonylation. This suggests that for an application of this remote carbonylation to the synthesis of mevalonolactone, beta-hydroxy group should be introduced after constructing the key delta-lactone skeleton.