A mixture of isomeric 9,10,12,13-tetrahydroxystearic acids (threo, threo, threo and threo, erythro, threo) can be prepared from anti-cis, cis-9,10,12,13-di-epoxystearic acid in over 80% yield by way of the intermediate di(hydroxy-alkoxysulfonium) salts and in ca. 68% yield by way of the intermediate di(hydroxy-formate) esters obtained by acid-catalyzed epoxide ring opening with dimethyl sulfoxide and formic acid, respectively. Mechanisms and stereochemistry of formation of the two isomers are discussed. Factors that influence the formation of cyclic products in competition with tetrahydroxystearic acids also are described. The key to the greatly improved yield of tetrahydroxystearic acids over prior literature procedures is avoiding water during ring opening of the protonated epoxide, as even small quantities of water cause marked reduction in yields of tetrahydroxystearic acids.
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