Methyl 2,3,4-tri-O-benzyl-a-D-glucopyranosid

Glycosylation of Methyl 2,3,4-tri-O-benzyl-a-D-glucopyranoside (21) with 3-Methoxy-2-pyridyl 2,3,4-tri-0-benzoyl-6-0-t-butyldimethylsilyl- -D-glucopyranoside (20)... 

The alcohols used were ethanol, methyl 2,3,4-tri-O-benzyl-a-D-glucopyranoside, and 4-nitrophenylethyl 2-azido-2-deoxy-4,6-0-benzylidene-a-D-mannopyranoside. A range of promoters were tried dimethyl(methylthio)-sulfonium triflate, methyl triflate, iodonium dicollidine perchlorate, and iodonium dicollidine triflate. Yields were in the 30-70% range. 

The rather laborious preparation of the starting substrates for the investigation of this glycosylation reaction is described in Scheme 31b. Various glycosyl donors of the gluco, galacto and marmo series were synthesized, either O-benzylated or O-benzoylated, whereas only methyl 2,3,4-tri-O-benzyl-a-D-glucopyranoside 67 was used as nucleophile. 

The behaviour of 6-(substituted methyl) ethers 28,30, and 32 of methyl 2,3,4-tri-O-benzyl-a-D-glucopyranoside and similar 4-0-derivatives of 2,3,6-tri-O-benzyl-a-D-glucopyranoside during... 

Stoicheiometric RuOyCCl was also used to oxidise several furanoses, partially acylated glycosides and l,4 3,6-dianhydrohexitols [317] pyranosides to pyrano-siduloses [313] methyl 2,3,6-tri-O-benzoyl-a-D-glucopyranoside and its C-4 epimer to the a-D-xy/o-hexapyranosid-4-ulose (Table 2.3) [317], and methyl 2,3,6-trideoxy-a-D-e 7f/tro-hexapyranoside to the -a-D-,g/yceri9-hexa-pyranosid-4-ulose, an intermediate in the synthesis of forosamine [318], It was also used to oxidise benzyl 6-deoxy-2,3-0-isopropylidene-a-L-mannopyranoside to the a-L-/yxo-hexapyranosid-4-ulose [319] and for oxidation of isolated secondary alcohol functions, e.g. in the conversion of l,6-anhydro-2,3-0-isopropylidene-P-D-man-nopyranose to the-P-D-/yxo-hexa-pyranos-4-ulose mannopyranose (Fig. 2.16, Table 2.3 [20, 320, 324]). 

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