O-Glycosyl trichloroacetimidates

Typical Procedure for the Glycosylation with O-Glycosyl Trichloroacetimidates... 

The great interest in C-glycosyl compounds is reflected in the extensive research in this field (204). Successful investigations with O-glycosyl trichloroacetimidates as glycosyl donors and phenol ethers (199,207,208), silyl enol ethers (205,206), trimethylsilyl cyanide (205,206), and allyltrimethylsi-lane (206) as C-acceptors underline the wide scope of these highly reactive glycosyl donors. 

These results demonstrate that O-glycosyl trichloroacetimidate-based oligosaccharide synthesis on solid support may eventually become a valuable alternative to solution-phase synthesis because useful experience is available for the selection of the polymer support and choice of the linker system and the glycosyl donor. Further standardization of the building blocks and the protective group pattern will finally provide the yields and the anomeric control in order to successfully plan automated syntheses of oligosaccharides also in a combinatorial manner. 

Besides oxygen, other nucleophiles have also been successfully employed as acceptors. For instance, N-, C-, S-, and / -glycosyl derivatives have been obtained from corresponding nucleophiles and O-glycosyl trichloroacetimidates in the presence of acid catalysts [1 ]. For instance, aryl-C-glycosjdes have been recently synthesized from phenols in an efficient Fries-type rearrangement reaction [37]. 

Thus, O-glycosyl trichloroacetimidates exhibit in terms of ease of formation, stability, reactivity, and general applicability outstanding glycosyl donor properties they resemble in various aspects the natural nucleoside diphosphate sugar derivatives. Thus, this method has become a very competitive alternative to the existing techniques. 

Schmidt, R R, Gaden, H, Jatzke, H, New catalysts for the glycosyl transfer with O-glycosyl trichloroacetimidates. Tetrahedron Lett., 31, 327-330, 1990. 

R. R. Schmidt and J. Michel, Direct O-glycosyl trichloroacetimidate formation. Nucleophilicity of the anomeric oxygen atom. Tetrahedron Lett. 25 821 (1984). 

H. Fisher, and R. R. Schmidt, Synthesis of unprotected O-glycosyl trichloroacetimidates structure assignment and new results, Synlett, p. 84 (1994). 

REACTIONS ON SOLID PHASE (a) Glycosidation O-Glycosyl Trichloroacetimidates, TMSOTf (cat.), CHjClj, 0 to 40 °C... 

The synthesis of C-glycosides has been of great interest [320]. C-Glycosylation of electron-rich compounds with O-glycosyl trichloroacetimidates continues to be a method of choice. This work is not discussed here in detail. A few references give an entry to the work in this field [321,322,323,324]. 

O-Glycosyl trichloroacetimidates have become popular because they are easily available, powerful glycosyl donors. Therefore, investigations were undertaken to provide glycosyl donors which follow the principle of 0-glycosyl trichloroacetimidate formation and activation. A short outline of this work is attached here. 

F. Roussel, L. Knerr, M. Grathwohl, and R. R. Schmidt, O-Glycosyl trichloroacetimidates bearing Fmoc as temporary hydroxy protecting group A new access to solid-phase oligosaccharide synthesis, Org. Lett., 2 (2000) 3043-3046. 

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