Synthesis of fully-substituted enediynes by the Corey-Winter reaction

Functionalized alkynes are oxidized to the corresponding a-diketones with catalytic RuO4 and NaIO4. Treatment of these diones with metal acetylenides then gives mixtures of erythro- and threo-1,5-hexadiyne-3,4-diols with good erythro-selectivity. Reaction of the erythro-diols with thiophosgene in the presence of n-BuLi or KH as base results in the formation of the corresponding cyclic thionocarbonates in moderate to good yields. Reaction of the cyclic thionocarbonates with 1,3-dimethyl-2-phenyl-1,3,2-diazaphospholidine at 40 degrees C results in the formation of enediynes substituted at the 3- and 4-positions. As anticipated fom the mechanism of the pericyclic syn-elimination, the erythro-thionocarbonates provide pure Z-enediynes.