Modulating Electrostatic Interactions in Ion Pair Intermediates To Alter Site Selectivity in the C-O Deoxygenation of Sugars.

Controlling which products one can access from the predefined biomass-derived sugars is challenging. Changing from CH2 Cl2 to the greener alternative toluene alters which C-O bonds in a sugar are cleaved by the tris(pentafluorophenyl)borane/HSiR3 catalyst system. This increases the diversity of high-value products that can be obtained through one-step, high-yielding, catalytic transformations of the mono-, di-, and oligosaccharides. Computational methods helped identify this non-intuitive outcome in low dielectric solvents to non-isotropic electrostatic enhancements in the key ion pair intermediates, which influence the reaction coordinate in the reactivity-/selectivity-determining step. Molecular-level models for these effects have far-reaching consequences in stereoselective ion pair catalysis.