An efficient one step dihydroxylation of 1,2-glycals with oxone in acetone

Tandem Epoxidation‐Alcoholysis or Epoxidation‐Hydrolysis of Glycals Catalyzed by Titanium(IV) Isopropoxide or Venturello’s Phosphotungstate Complex

“…The influence of the nature of the protecting groups and pattern of protection can be evaluated by comparing results for reactions in ethanol. For fully protected glucals, reactivity decreases in the order Bn > Me > TBDMS (entries 13,16,18). The low reactivity of the TBDMS-protected glucal can be attributed to the significant steric demand of the bulky TBDMS groups which forces the glucal into the 5 H 4 conformation, where the substituents at C-3, C-4 and C-5 are in a pseudo-axial orientation.…”

“…Although these diols are synthetically very useful compounds (vide supra, Introduction), only a few methods for their selective preparation have been reported [6b,d,12-14] . The existing methods for direct dihydroxylation of glycals all have drawbacks such as the removal of Os salts [12][13][14] problems in scaleup in the case of DMDO, [13] formation of C-2 epimers or use of high mol% of metal. [14] In a first approach, the same reaction conditions as for the incorporation of long-chain alcohols were used, but the nucleophile was replaced by an excess of water.…”

“…Selective dihydroxylation of benzylated glucal. 1 H, 13 C NMR, COSY, HSQC and DEPT analysis. With complex mixtures, the products were acetylated (Ac 2 O, pyridine) and analyzed by NMR.…”

“…The organic phase was dried with MgSO 4 , filtered and concentrated under vacuum, and then acetylated (Ac 2 O, pyridine). The identity of products and the ratio of stereoisomers was determined by analysis of the mixtures by 1 H and 13 C NMR, and COSY, HSQC and DEPT analysis. Where necessary, separation and purification of products was achieved by chromatography on a column of silica gel using mixtures of ethyl acetate and hexane as eluent.…”

“…In one of the earliest reports on the matter, Bilik et al [12] used a range of metal oxides among which MoO 3 gave the best results. Other methods include the use of oxone-acetone, [13] OsO 4 -NMO [14] and the bimetallic system RuCl 3 /CeCl 3 /NaIO 4 . [15] Against this background we here present a methodology for the selective formation of a-epoxides from protected glycals, followed by in situ opening of the epoxides to give either 2-hydroxyglycosides or sugar 1,2-diols.…”