ABSTRACT
Cyclic Sulfates) .......................................................................................................... 233
6.4 Halogenation Reactions ...................................................................................................... 235
6.4.1 S
2 Displacements of Sulfonates .............................................................................. 235
6.4.2 S
2 Opening of Epoxides .......................................................................................... 236
6.4.3 Use of Alkylphosphonium Salts ................................................................................ 237
6.4.4 Use of Chlorosulfate Esters ....................................................................................... 238
6.4.5 Use of Iminoesters and Sulfonylchlorides ................................................................ 238
6.4.6 Fluorination Reactions ............................................................................................... 239
6.4.7 Halogenation of O-Benzylidene Acetals ................................................................... 239
6.4.8 Radical Processes ....................................................................................................... 241
6.5 Reactions Involving Nitrogen ............................................................................................. 241
6.5.1 S
2 Reactions ............................................................................................................ 241
6.5.2 Formation of Nitrosugars .......................................................................................... 243
6.5.3 The Mitsunobu Reaction ........................................................................................... 243
6.6 Reactions Involving Oxygen and Sulfur ............................................................................ 244
6.6.1 Manipulation of Sugar Hydroxyl Groups ................................................................. 244
6.6.1.1 Formation of Epoxysugars (Anhydrosugars) ............................................... 244
6.6.1.2 Ring Opening of Epoxides ........................................................................... 244
6.6.1.3 Inversion of Stereocenters ............................................................................ 245
6.6.2 Deoxygenation Reactions .......................................................................................... 245
6.6.2.1 Removal of Hydroxyl Groups ...................................................................... 245
6.6.2.2 Elimination/Dehydration to Olefins ............................................................. 246
6.6.2.2.1 1,2-Unsaturated Sugars (Glycals) ................................................ 246
6.6.2.2.2 2,3-Unsaturated Sugars ................................................................ 247
6.6.2.2.3 3,4-Unsaturated Sugars ................................................................ 247
6.6.2.2.4 4,5-Unsaturated Sugars ................................................................ 248
6.6.2.2.5 5,6-Unsaturated Sugars ................................................................ 248
6.6.3 Sulfuration Reactions ................................................................................................. 249
6.6.4 Desulfuration Reactions ............................................................................................. 250
6.7 Formation of Carbon-Carbon Bonds ................................................................................. 251
6.7.1 Addition of Nucleophiles .......................................................................................... 251
6.7.1.1 Grignard Reagents ........................................................................................ 251
6.7.1.2 Organosodium, Organolithium and Organopotassium Reagents ................ 252
6.7.1.3 Cuprates ........................................................................................................ 252
6.7.1.4 Sulfur Ylide Epoxidations/Wittig Reactions on Epoxides .......................... 253
6.7.2 Condensation Reactions ............................................................................................. 254
6.7.2.1 The Cyanohydrin Chain Extension .............................................................. 254
6.7.2.2 The Nitromethane Condensation ................................................................. 255
6.7.3 Wittig/Horner-Emmons Reactions ........................................................................... 256
6.7.4 Claisen Rearrangements ............................................................................................ 256
6.8 Reductions and Oxidations ................................................................................................. 257
6.8.1 Reduction Reactions .................................................................................................. 257
6.8.1.1 Reduction of Halides and Sulfonates ........................................................... 258
6.8.1.2 Reduction of Epoxides ................................................................................. 259
6.8.1.3 Reduction of Olefins .................................................................................... 259
6.8.1.3.1 Catalytic Methods ........................................................................ 259
6.8.1.3.2 Hydroborations ............................................................................. 260
6.8.2 Oxidation Reactions ................................................................................................... 260
6.9 Rearrangements and Isomerizations ................................................................................... 261
6.9.1 Base Catalyzed Isomerizations .................................................................................. 261
6.9.2 The Amadori Rearrangement .................................................................................... 261
6.10 Conclusion ....................................................................................................................... 263
References ................................................................................................................................... 263
The chemical modification of sugars to sugar derivatives or nonsugar products has been extensively
studied as a strategy to prepare products ranging from rare sugars to novel chiral substances and to
complex natural products. The methods utilized in the initial transformations are generally drawn
from the principles of mainstream organic chemistry. In this chapter, many of these strategies are
addressed. One should realize, however, that any one of the strategies presented herein could form
the basis of a complete chapter in this book. In the interest of describing principles readily adaptable
to the direct modification of sugars, this chapter makes extensive use of historical literature
highlighting basic strategies. It is not the intent of this chapter to present an exhaustive analysis of
this subject but rather to present ideas which, through the incorporation of basic organic chemistry
principles, will lead the reader towards desired solutions to more complex problems.
