A Simplified, One-Pot Preparation of Acetobromosugars from Reducing Sugars

Acetobromoglycoses continue to be important as glycosyl donors in the synthesis of simple glycosides as well as complex oligosaccharides. From reducing sugars they are usually prepared via their peracetates in two steps. In the first step, sugars are converted to their peracetates using pyridine and acetic anhydride1,2 and the acetates are then converted in a second step to acetobromosugars using a solution of hydrogen bromide in glacial acetic acid(HBr/HOAc).2 Although not in use very often Redemann and Niemann3 as well as Lemieux4 have described one-pot methods for the preparation of acetobromoglucose wherein the reducing sugar is first treated with acetic anhydride in the presence of sulfuric acid3 or perchloric acid4 respectively to afford the peracetate. Direct conversion of the peracetate to its 1-bromo-derivative, in yields ranging from 80-87%, was then achieved by either treating the solution of the peracetate with gaseous HBr3 or with bromine in the presence of red phosphorus.4 In anothe...