Thioglycosides 1-benzenesulfinyl

To a solution of thioglycoside (1.0 equiv), 1-benzenesulfinyl piperidine (1.0 equiv), TTBP (2.0 equiv), and freshly activated 3 A powdered molecular sieves in dichloromethane (25.0 ml mmol-1) was added trifluoromethanesulfonic anhydride (1.1 equiv) at —60 °C under an argon atmosphere. The reaction mixture was stirred for 5 min, after that a solution of the glycosyl acceptor (1.5 equiv) in dichloromethane (4.0 ml mmol-1) was added. The reaction mixture was stirred at — 60 °C for 2 min, after that it was slowly warmed to room temperature and quenched by the addition of saturated aqueous NaHC03. The organic layer was washed with brine, dried (MgS04), filtered and the filtrate was concentrated to dryness. Purification of the crude product by column chromatography over silica gel afforded the product. 

Crich, D, Smith, M, 1-Benzenesulfinyl piperidine/trifluoromethanesulfonic anhydride a potent combination of shelf-stable reagents for the low-temperature conversion of thioglycosides to glycosyl triflates and for the formation of diverse glycosidic hnkages, J. Am. Chem. Soc., 123, 9015-9020, 2001. 

Furthermore, these authors were also able to perform the -mannosylations with the thiogly-coside 35 under the action of PhSOTf [45] or 1-benzenesulfinyl piperidine (BSP)-Tf20 [46] (O Scheme 17). In the cases of both glycosyl sulfoxide and thioglycoside, protection of the 4- and 6-positions by a cyclic acetal is critical. The corresponding perbenzylated donors gave poor -selectivity [47]. 

Crich D, Banerjee A, Li W, Yao Q. Improved synthesis of 1-benzenesulfinyl piperidine and analogs for the activation of thioglycosides in conjunction with trifluoromethanesulfonic anhydride. J Carbohydr Chem 2005 24 415-424. 

Subsequent variations on the theme include benzenesulfinyl pyrrolidine firom the Crich laboratory, for use in low temperature NMR experiments because of its greater solubility than BSP [37], benzenesulfinyl morpholine by the Huang group [38], and lV-(phenylthio) E-caprolactam by Wong and coworkers [39]. Later, it was shown by Tatai and Fiigedi that even the combination of dimethyl disulfide with triflic anhydride is a powerful system for the activation of thioglycosides at low temperature [40]. 

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