ABSTRACT
Glycosyl chlorides constitute an important class of glycosyl donors for synthesis of oligosaccharides,1 O-glycosides,2 C-glycosides,3a N-glycosides,3b and glycals.4 Typical preparation of glycosyl chlorides involves treatment of glycosyl derivatives
Introduction .............................................................................................................. 73 General TCT/DMF Chlorination Protocols ............................................................. 75 Experimental Methods ............................................................................................. 75
General Methods ................................................................................................. 75 TCT/DMF Chlorination Protocol A for Preparation of Glycosyl Chlorides 1a and 2a ............................................................................................................. 76 TCT/DMF Chlorination Protocol B for Preparation of Glycosyl Chlorides 3a and 4a ............................................................................................................. 76
2,3,4,6-Tetra-O-Acetyl-α-d-Glucopyranosyl Chloride (1a) ........................... 76 2,3,4,6-Tetra-O-Acetyl-α-d-Mannopyranosyl Chloride (2a) .........................77 2,3,4,6-Tetra-O-Benzyl-α-d-Galactopyranosyl Chloride (3a) .......................77 2,3:5,6-Di-O-Isopropylidene-α-d-Mannofuranosyl Chloride (4a) ................77
Acknowledgment ..................................................................................................... 78 References ................................................................................................................ 81
with acidic chlorinating reagents. However, strongly acidic conditions are incompatible with many acid-labile protecting functions; consequently, application of this methodology is limited.5,6 Although there are milder reagents for chlorination of glycopyranoses such as PPh3-CCl4,7a Viehe’s salt,7b chloroenamine,7c chlorodiphenyl phosphate,7d triphosgene,7e and dichloromethyl methyl ether,7f,g each of these methods has its limitations. For example, the use of Viehe’s salt or chloroenamine needs additional preparatory steps,7b,7c while triphosgene chlorination reagent is less effective for disarmed glycosyl substrates.7e Accordingly, developing milder and more general chlorination methods remains desirable.
