104
2
General Synthetic Methods
3
Reactions at the Anomeric Hydroxyl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
3.1
Alkylation Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
3.1.1 Anomeric O-Alkylation and O-Arylation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
3.1.2 Anomeric O-Dealkylation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
3.2
Acylation Reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
3.2.1 Anomeric O-Acylation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
3.2.2 Anomeric O-Deacylation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
3.3
Carbonylation and Thiocarbonylation of the Anomeric Hydroxyl. . . . . . . . . . . . . . . 165
3.4
Silylation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
3.5
Phosphorylation and Phosphitylation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
Abstract
Synthetic protocols based on carbohydrates require the differentiation of their abundant
hydroxyl groups, by and large, in order to expose just one single hydroxyl group to the
selected reagent. This differentiation is usually carried out with the assistance of protecting
groups that block the rest of the hydroxyl groups while being compatible with the given
reaction conditions. By corollary, the knowledge and apt choice of the appropriate protecting
groups is a key factor in successful synthetic endeavors. In this chapter, an overview of the
most commonly employed protecting groups in carbohydrate chemistry is given. Alkyl ethers,
being robust protecting groups, have a long history in synthetic carbohydrate chemistry and
in related structural studies of polysaccharides. Acetals and ketals, which are of fundamental
importance in carbohydrate chemistry, are then discussed. Acyl and silyl protecting groups,
which also play an important role in modern monosaccharide transformations, are also presented. Finally, recent blocking strategies are described, including orthogonal strategies, by
which the protecting groups are harmoniously combined in modern carbohydrate chemistry.
Keywords
Protecting groups; Alkylation; Acetalation; Acylation; Carbonylation; Silylation;
Phosphorylation
Abbreviations
ADMB
4-acetoxy-2,2-dimethylbutanoyl
All
allyl
Alloc or Aloc
allyloxycarbonyl
APAC
2-(allyloxy) phenyl acetyl
BDA
butane 2,3-diacetals
Bn
benzyl
Bocdene
2-(tert-butoxycarbonyl)-ethylidene
BOM
benzyloxymethyl ether
Bz
benzoyl
BzOBT
1-N-benzyloxy-1,2,3-benzotriazol
2
General Synthetic Methods
3
Reactions at the Anomeric Hydroxyl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
3.1
Alkylation Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
3.1.1 Anomeric O-Alkylation and O-Arylation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
3.1.2 Anomeric O-Dealkylation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
3.2
Acylation Reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
3.2.1 Anomeric O-Acylation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
3.2.2 Anomeric O-Deacylation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
3.3
Carbonylation and Thiocarbonylation of the Anomeric Hydroxyl. . . . . . . . . . . . . . . 165
3.4
Silylation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
3.5
Phosphorylation and Phosphitylation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
Abstract
Synthetic protocols based on carbohydrates require the differentiation of their abundant
hydroxyl groups, by and large, in order to expose just one single hydroxyl group to the
selected reagent. This differentiation is usually carried out with the assistance of protecting
groups that block the rest of the hydroxyl groups while being compatible with the given
reaction conditions. By corollary, the knowledge and apt choice of the appropriate protecting
groups is a key factor in successful synthetic endeavors. In this chapter, an overview of the
most commonly employed protecting groups in carbohydrate chemistry is given. Alkyl ethers,
being robust protecting groups, have a long history in synthetic carbohydrate chemistry and
in related structural studies of polysaccharides. Acetals and ketals, which are of fundamental
importance in carbohydrate chemistry, are then discussed. Acyl and silyl protecting groups,
which also play an important role in modern monosaccharide transformations, are also presented. Finally, recent blocking strategies are described, including orthogonal strategies, by
which the protecting groups are harmoniously combined in modern carbohydrate chemistry.
Keywords
Protecting groups; Alkylation; Acetalation; Acylation; Carbonylation; Silylation;
Phosphorylation
Abbreviations
ADMB
4-acetoxy-2,2-dimethylbutanoyl
All
allyl
Alloc or Aloc
allyloxycarbonyl
APAC
2-(allyloxy) phenyl acetyl
BDA
butane 2,3-diacetals
Bn
benzyl
Bocdene
2-(tert-butoxycarbonyl)-ethylidene
BOM
benzyloxymethyl ether
Bz
benzoyl
BzOBT
1-N-benzyloxy-1,2,3-benzotriazol