Thioacetal interchange

Treatment of 649 with ethanedithiol in the presence of boron trifluoride etherate results in acetal—thioacetal interchange at C-6 and subsequent lactonization of the 4)5-hydroxyl group with the r/-butyl ester, thus furnishing 651 in 83% yield. Reduction of the lactone to a lactol, protection with a MOM group, hydrolysis of the thioacetal, and reduction of the ketone with lithium aluminum hydride gives 653 as a single product. After benzoylation of the alcohol, conversion of the OMOM derivative to carboxamide (OMOM —> OAc CN — CONH2) affords 140 as a 10 1 mixture of isomers. 

The oxygen-sulfur interchange reaction was extended to an acyclic anhydride system. High conversion of acetic anhydride to a mixture of thioacetic acid and acetic acid was obtained employing alkali metal... 

Thioacetal—hemithioacetal—acetal interchange. Corey and Hase have disclosed a method for direct interchange of these functional groups under neutral conditions. The method is formulated for acetal interchange of heptanal. 

INTERCHANGE, THIOACETAL-HEMITHIOACETAL-ACETAL Methyl fiuorosulfonate. lODOCYCLOPROPANATION Diethylzinc-Iodoform. 

Corey and Hase have found that 1,3-dithiolans and 1,3-dithians can be converted in good yields into dimethyl acetals, cyclic acetals, or thioacetals (or thioketals) upon reaction of the mono-5-methylated derivatives with methanol, ethylene glycol, and mercaptoethanol, respectively. These interchanges do not appear to involve the free carbonyl compound. The disulphonium salt prepared by the reaction of triethyloxonium tetrafluoroborate with 2-phenyl-l,3-dithiolan can be used to prepare benzylidene derivatives of 1,2-, 1,3-, and 1,4-diols (30— 80%) under basic conditions. This reaction appears to have considerable potential as a route to benzylidenated sugars. 

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