An Improved Protocol for the Stereoselective Synthesis of β-d-Glycosyl Fluorides from 2- O -Acyl Thioglycosides.

A safe and operationally simple protocol for the preparation of β-d-glycosyl fluorides is presented. We demonstrate that a precise combination of XtalFluor-M, N -bromosuccinimide, and Et 3 N·3HF can mediate facile, high-yielding, and diastereoselective conversions of 2- O -acyl thioglycosides to β-d- and other 1,2- trans glycosyl fluorides. The key roles of these reagents are dissected in this work, as is the impact of their interplay on the fluorination stereoselectivity.