Previous studies on glycosylation reactions of fully oxygenated α-glycosyl donors promoted by bis-thiourea HBD catalysts have provided evidence that β-selectivity arises from predominant stereoinvertive substitution at the anomeric position. However, and as noted above, 2-deoxyglycosyl donors are far more prone to undergo epimerization or substitution via SN1 pathways (Figure ). To probe the origin of β-selectivity in 2-deoxyglucosylations promoted by 1a, compound 2a was prepared in two different levels of anomeric purity (α:β = >20:1 and 3.3:1) and subjected to the optimized reaction conditions for glucosylation of 3a and 4a. Very similar β-selectivities were observed regardless of the anomeric purity of 2a (Figure ). These results are consistent with product distribution governed by either Curtin-Hammett control over rapidly equilibrating anomers of 2a, stereospecific reaction via a single anomer of 2a, or stereoselective nucleophilic substitution through a common reactive intermediate. To distinguish these two scenarios, the glycosylation of 3b with different anomeric mixtures of 2a (α:β = >20:1 and 2.5:1) was halted at low conversion and the anomeric composition of unconsumed 2a in each reaction was determined (Figure ). The observed lack of convergence in the anomeric ratio of 2a, despite a significant degree of product formation, is inconsistent with the rapid equilibration reflective of Curtin-Hammett control. In contrast to the findings depicted in Figure , an analogous set of experiments with the 2,6dideoxyglucosyl phosphate revealed different levels of β-selectivity are obtained using 2b with different initial levels of anomeric purity (Figure ). Thus, the two different classes of deoxyglucosyl phosphates appear to undergo substitution with different levels of stereospecificity. Heterogenous additives play a critical role in the deoxyglucosylation reactions described above. As in previously studied HBD-catalyzed glycosylations with glycosyl phosphates, added 4Å molecular sieves are required to sequester the phosphoric acid byproduct formed during the glycosylation. Our present study has further shown that use of basic alumina improves the β-selectivity of phenolic 2deoxyglucosylations. In the absence of both 4Å molecular sieves and basic alumina, α-enriched 2,6-dideoxyglucosyl phosphate 7a was observed by NMR to undergo anomerization to approximately 6:1 α:β mixtures, followed by rapid decomposition (Figure ). Anomerization was not observed in the presence of 4Å molecular sieves, indicating that small amounts of phosphoric acid likely promotes the anomerization process. In addition, the combination of basic alumina and 4Å molecular sieves was found to improve the efficiency of sequestering soluble phosphoric acid (Figure ). We propose that such efficient sequestration is needed for reaching optimal levels of β-selectivity in phenolic glucosylations by suppressing both undesired, phosphoric acid-catalyzed background reactions as well as in situ anomerization to β-phosphates. However, low concentrations of soluble phosphoric acid do not appear to have the same deleterious effect on glucosylations of alcohols. In summary, we have developed catalytic and β-selective 2deoxy and 2,6-dideoxyglucosylations, providing a viable new approach to these longstanding challenges in glycosylation chemistry. The versatility of these methods is demonstrated by the successful synthesis of 2-deoxyglucosides with various nucleophiles featuring both acid-and basesensitive functionalities. Successful glucosylations with both 2-deoxy and 2,6-dideoxysugars necessitated specific modifications to electrophiles and catalysts. Together with the observation of different degrees of stereospecificity between these two systems, our results underscore the challenges of stereoselective glycosylations with deoxy sugars. We are hopeful that the strategies applied in this work will help spur further advances in selective glycosylation with different classes of deoxysugars.