716
3
Chemical Glycosylation Reactions
⊡ Scheme 25
⊡ Scheme 26
⊡ Scheme 27
An elimination reaction was also successfully used in the synthesis of furanoid glycals from
2-deoxyribose. The substrates used were 2-deoxy-1-seleno-furanosides 75, which were transformed to their respective glycals 76 via selenoxide elimination in yields ranging from 71 to
85% ( > Scheme 26) [167].
A one-pot, two-step reaction leading to glycals from 2-deoxyhexopyranoses silylated or acetylated at the anomeric center or from 2-deoxyhexopyranosides can be considered a method of
choice because of its high yield and simplicity. The two-step reaction includes addition of
trimethylbromosilane (TMSBr) to 77 or 79 (generation of glycosyl bromide) and subsequent
addition of N,N-diisopropylethylamine to cause elimination to glycals 78 and 80, respectively( > Scheme 27). In all cases, yields of isolated product exceeded 90% [163,168,169].
7 Reactions Involving 2,3-Unsaturated
Saccharide-to-Glycal and Glycal-to-Glycal Rearrangements
Esterified glycals 81 easily undergo reaction with nucleophiles, typically under Lewis acid
catalysis to 2,3-unsaturated pyranoses 82. This reaction is known as Ferrier rearrangement [7].
3
Chemical Glycosylation Reactions
⊡ Scheme 25
⊡ Scheme 26
⊡ Scheme 27
An elimination reaction was also successfully used in the synthesis of furanoid glycals from
2-deoxyribose. The substrates used were 2-deoxy-1-seleno-furanosides 75, which were transformed to their respective glycals 76 via selenoxide elimination in yields ranging from 71 to
85% ( > Scheme 26) [167].
A one-pot, two-step reaction leading to glycals from 2-deoxyhexopyranoses silylated or acetylated at the anomeric center or from 2-deoxyhexopyranosides can be considered a method of
choice because of its high yield and simplicity. The two-step reaction includes addition of
trimethylbromosilane (TMSBr) to 77 or 79 (generation of glycosyl bromide) and subsequent
addition of N,N-diisopropylethylamine to cause elimination to glycals 78 and 80, respectively( > Scheme 27). In all cases, yields of isolated product exceeded 90% [163,168,169].
7 Reactions Involving 2,3-Unsaturated
Saccharide-to-Glycal and Glycal-to-Glycal Rearrangements
Esterified glycals 81 easily undergo reaction with nucleophiles, typically under Lewis acid
catalysis to 2,3-unsaturated pyranoses 82. This reaction is known as Ferrier rearrangement [7].