Glycosylations trifluoromethanesulfonic anhydride

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. 

The most common activator for the glycosyl sulfoxides is trifluoromethanesulfonic anhydride (triflic anhydride), which, in the absence of nucleophiles, rapidly and cleanly converts most sulfoxides into the corresponding glycosyl triflates in a matter of minutes at —78 °C in dichloromethane solution [86,280,315,316]. In the more extensively studied mannopyranose series, only the a-mannosyl triflate is observed by low-temperature NMR spectroscopy (Scheme 4.35) [280]. In the glucopyranose series, mixtures of a- and (1-triflates are observed, in which the a-anomer nevertheless predominates (Scheme 4.36) [280],... 

Crich, D, Smith, M, 5 -(4-Methoxyphenyl) benzenethiosulfinate (MPBT)/trifluoromethanesulfonic anhydride a convenient system for the generation of glycosyl triflates from thioglycosides, Org. Lett., 2, 4067-4069, 2000. 

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. 

Garcia, B A, Poole, J L, Gin, D Y, Direct glycosylations with 1-hydroxy glycosyl donors using trifluoromethanesulfonic anhydride and diphenyl sulfoxide, J. Am. Chem. Soc., 119, 7597-7598, 1997. 

Kim and co-workers carried out a closely related synthesis of a /<-(l -4)-mannote-traose 300, using their method for the in situ conversion of hemiacetals to glycosyl triflates by means of reaction with phthalic anhydride ( phthalan ) followed by trifluoromethanesulfonic anhydride. In this instance cleavage of the benzylidene acetal was effected with trifluoroacetic acid, and regioselective reprotection of the diol employed benzoyl chloride (Scheme 50).145... 

K. S. Kim, D. B. Fulse, J. Y. Baek, B.-Y. Lee, and H. B. Jeon, Stereoselective direct glycosylation with anomeric hydroxy sugars by activation with phthalic anhydride and trifluoromethanesulfonic anhydride involving glycosyl phthalate intermediates, J. Am. Chem. Soc., 130 (2008) 8537-8547. 

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