670
3
Chemical Glycosylation Reactions
⊡ Scheme 13
⊡ Scheme 14
⊡ Scheme 15
⊡ Scheme 16
⊡ Scheme 17
The use of diphenyl phosphorochloridate or tosyl chloride and sodium N,N-diethyldithiocarbamates under phase-transfer conditions yields the S-glycosyl diethyldithiocarbamates through
intermediate 1-O-diphenylphosphates or tosylates, respectively [85] ( > Scheme 15).
Similarly, perbenzylated glucopyranose and ribofuranose almost quantitatively yield the
phenyl thioglycoside when reacted with thiophenol and catalytical amounts of methoxyacetic
acid and ytterbium triflate ( > Scheme 16) [86].
An alternative is, of course, to convert the hemiacetals to isolable derivatives with better anomeric leaving groups, e. g., acetates ( > Sect. 2.1.1), halogens ( > Sect. 2.1.2), or
trichloroacetimidates ( > Sect. 2.1.4). 1-O-Trimethylsilyl derivatives can also be smoothly
converted to the corresponding thioglycoside through the reaction with a thiol and BF 3 -etherate ( > Scheme 17) [83]. Since no participating groups were involved predominantly α-thioglycosides were produced.
3
Chemical Glycosylation Reactions
⊡ Scheme 13
⊡ Scheme 14
⊡ Scheme 15
⊡ Scheme 16
⊡ Scheme 17
The use of diphenyl phosphorochloridate or tosyl chloride and sodium N,N-diethyldithiocarbamates under phase-transfer conditions yields the S-glycosyl diethyldithiocarbamates through
intermediate 1-O-diphenylphosphates or tosylates, respectively [85] ( > Scheme 15).
Similarly, perbenzylated glucopyranose and ribofuranose almost quantitatively yield the
phenyl thioglycoside when reacted with thiophenol and catalytical amounts of methoxyacetic
acid and ytterbium triflate ( > Scheme 16) [86].
An alternative is, of course, to convert the hemiacetals to isolable derivatives with better anomeric leaving groups, e. g., acetates ( > Sect. 2.1.1), halogens ( > Sect. 2.1.2), or
trichloroacetimidates ( > Sect. 2.1.4). 1-O-Trimethylsilyl derivatives can also be smoothly
converted to the corresponding thioglycoside through the reaction with a thiol and BF 3 -etherate ( > Scheme 17) [83]. Since no participating groups were involved predominantly α-thioglycosides were produced.