Hi!

I'm performing a reaction that replaces an acetate group on the anomeric carbon of a sugar with a bromoethanol. The reaction conditions are as follows:

Sugar

Bromoethanol

catalytic ZnCl2

BF3*Et2O

In DCM, stir at roomtemp overnight

My question is what is the purpose of the ZnCl2? Since ZnCl2 and BF3 are lewis acids, wouldn't you need only one or the other?

Thanks in advance!