Replacement of Alkylthio Groups by Halogen Atoms

The action of limited amounts of active halogen compounds in aprotic solvents converts protected dithioacetals into 1-halo-1-thioal- 

AcOCH Br2—Et2Q, or AcOCH POCI3 or AcOCH AcOCH MeOCH2Br AcOCH MeOCH2Cl AcOCH HCOAc HCOAc HCOAc 

The different reactivities of the two substituents on C-l allow selective replacement and conversion of them. Alkyl monothio-acetals [proposed as intermediates in mercury(II)-catalyzed demer-captalation reactions—see Section IV,l,b] have been prepared from a-bromothioethers by the combined action of an alcohol and silver(I) carbonate the introduction of S-nucleophiles is discussed in Section 11,6. Reduction of 81 by lithium aluminum hydride effects hydrogen-olysis of the carbon-halogen bond, whereas the action of Raney nickel on the derived S-ethyl O-methyl monothioacetal specifically cleaves the carbon-sulfur bond to afford the pentaacetate of 1-0-methyl-D-galactitol.327 

The deprotected, epimeric products (151) of condensation of 81 with 6-acylamido-9-(chloromercuri)purine are formally related to 9-glycosyladenines, and Wolfrom and coworkers329 coined the term acyclic nucleoside analogues to describe such compounds. A 

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