Sulfoxide hemiacetal activation

In addition to sulfoxides, sulfides activated by triflic anhydride also provide oxosulfonium ions. In these reactions, the triflic anhydride serves as the oxidant. Thus, hemiacetals were activated by dimethyl sulfide and triflic anhydride providing glycosides in good yields [419]. 

In glucosides, hemiacetal hydroxyl activation/substitution can be achieved using a sulfonic anhydride and a nucleophile, plus a base as acid scavenger.12 The reaction is catalysed by dibutyl sulfoxide (Bu2S=0), and shows evidence of sulfur-covalent catalysis. Using benzenesulfonic anhydride [(PhS0)20], it is proposed to involve initial formation of a sulfonium sulfonate (6), the S(IV) centre of which then reacts with... 

Garegg,95,96 and others97,98 involved the activation of alkyl halides over S -alkyl/aryl glycosides. Subsequently, other examples of suitable LGa for selective activations have become available trichloroacetimidates,99,100 phosphite,101 phosphate,102 thioi-midate,103-106 thiocyanate,107,108 hemiacetal,109,110 sulfoxide,111,112 selenoglyco-side,113-116 orthoester,76,117-119 O-hetaryl,120-122 and others.123-129 Many of these couplings were performed with the use of S -alkyl/aryl, fluoro, or O-al kenyl/hetary 1 moieties as LGb. 

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