Recent advances in the synthesis of 2-deoxy-glycosides

Stereoselective Tandem Epoxidation–Alcoholysis/Hydrolysis of Glycals with Molybdenum Catalysts

“…[44d] In the late 1990s, Adam et al proposed a transition state structure for the Tiand Mo-TBHP epoxidation of chiral allylic alcohols, mainly dominated by 1,3 A strain, where the preferred dihedral angle a for the epoxidation of the peroxy complex lies between 708 and 908. On the basis on the similar diastereoselectivity ratios of Ti and Mo systems of the epoxidation reactions of chiral allylic alcohols and relating them with the regio-and diastereoselective epoxidation of 1-methylgeraniol with Ti, they proposed for both metals, a metal-alcoholate complex model.…”

“…However, in spite of the results previously mentioned using MoO 3 and the facts that molybdenum complexes are readily available and one of the most active and efficient catalysts for alkene epoxidation, [24] no systematic investigations of their use in glycal epoxidation-alcoholysis or epoxidation-hydrolysis have been carried out. In this report we show that a variety of molybdenum complexes catalyze these processes with high conversions and selectivities.…”

“…[22] The transition metal-catalyzed processes aforementioned mostly afford products mainly derived of the epoxidation trans to the C-3 substituent (Scheme 1b). Interestingly, the dihydroxylation (epoxidation/hydrolysis) of unprotected glucal using MoO 3 as a catalyst in water as a solvent affords mainly mannose, in a process that involves directed b-epoxidation, probably via a hydrogen bond between the neighbouring allylic hydroxy group and the catalyst. [23] Only Venturellos peroxotungstate (PW 4 O 24 3À ) [19] provided a similar selectivity in unprotected glycals.…”

“…Catalysts for epoxidation of glycals have only recently been identified. Thus, Ru-porphyrin, [16] CH 3 ReO 3 (MTO), [17,18] TiA C H T U N G T R E N N U N G (O-i-Pr) 4 [19] and Venturellos peroxotungstate (PW 4 O 24 3À ) [19] have been used in the sequential epoxidation-alcoholysis or epoxidation-hydrolysis of glycals. The epoxides initially obtained are opened in situ to give 2-hydroxy glycosides or dihydroxy derivatives in the presence of the epoxidation catalysts, depending on whether the reaction is carried out in the presence of alcohols or …”

“…[1] This fact has spurred the research for new synthetic methodologies looking for an easy and selective access to these compounds. In this way glycals are versatile building blocks for the synthesis of oligosaccharide motifs, [2] 2-deoxyglycosides, [3] C-glycosides, [4] nucleosides [5] and other biologically important molecules. [6][7][8] Glycals are usually activated by epoxidation, [9] to furnish 1,2-anhydro sugars, which are used as glycosyl donors [2] or as precursors of more stable glycosyl donors.…”