Use of anomeric acetates as glycosyl donors

The synthesis of 2-bromoethyl 2,3,4,6-tetra-0-acetyl-(3-D-glucoside from D-glucose pentaacetate [10, 11], 

Notes and discussion. Note the use of 5 equiv. of boron trifluoride etherate in this procedure. Use of fewer equivalents ( 5 equiv.) results in a sluggish, low yielding reaction. 

Here the glycosyl acceptor contains a group (bromide) that is incompatible with the use of a soft Lewis acid activator and so precludes the use of some alternative glycosylation donors, such as glycosyl bromides or thioglycosides. As a consequence of anchimeric assistance by the C-2 acetate group, the (3-glucoside is the major product. 

2-Bromoethanol (distilled from CaO, 0.45 ml, 6.3 mmol) Dichloromethane (9 ml distilled from CaHa) 

Nitrogen source/balloon and bubbler head/septum Ice bath 

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