Mesylation axial

Dimethyl sulfoxide (DMSO) has been used to effect the elimination of sulfonates at elevated temperatures (see, for example, ref. 237). Benzene-sulfonates are recommended. The elimination of a variety of sulfonates proceeds readily in this medium in the presence of potassium /-butoxide. A -Compounds have been formed at 100°, but heating is not necessary. The effects of temperature change, orientation of the hydroxy group and changes in the sulfonate employed have been examined. The principal side reaction appears to be formation of the original alcohol (uninverted), particularly with equatorial mesylates at low temperatures it is minimized with axial tosylates. 

This is likely due to four groups on the ring being in the axial position. We were successful by protecting the alcohol as the mesylate, but further reactions did not prove fruitful in moving forward in the total synthesis. These reactions, as well as optimization of the hydroboration described, are discussed in detail in [48]. 

Many deoxy-sugars are synthesized by conventional methods of dehalogenation or reduction of thiocarbonates tosylates, mesylates etc. One notable exception, involving dimerization of phenylselenyl 2-deoxy-D-glucopyranose in a concentrated solution and in the absence of trapping agents is worthy of mention as it is related to the chemical character of the free radical intermediate. The approach proceeds by the formation of the axial-axial coupling product as the major one and axial-equatorial as the minor product. 

A synthesis of methyl a-D-sibirosaminide (23) has been reported (Scheme 3), which starts from a 3-C-methylaltropyranoside derivative, and Dyong and Schulte have described the synthesis of a closely related compound (24) from the 2-deoxy-3-ulose (25), which required introduction of the 2-hydroxy-group by means of a [2,3]-sigmatropic rearrangement (Scheme 4). The addition of HCN to the threo-analogue of (25) in the presence of pyridine afforded the kinetic cyanohydrin (axial attack) in 74% yield, whereas in the presence of sodium bicarbonate the thermodynamic product with the opposite configuration was obtained. The two products were isolated as their mesylates, which were... 

In 2009, Garcia Ruano et al. demonstrated that enantiomerically pure 2-(/ -tolysulfinyl)benzylcopper reagents reacted with racemic propargylic mesylates, affording the corresponding chiral allenes with central and axial chirality. These reactions took place in a completely regioselective Sn2 ... 

There are relatively many stereoselective synthetic methodologies for synthesizing these compounds. The one reported by Bundle and co-workers takes advantage of the synthetic utility of functionalized 1,2-oxazolines (Scheme 9). The synthetic sequence requires a stereoselective opening of 1,2-oxazoline with the formation of methyl 2-aminoglucoside in the pyranose form. The C-3 mesylated derivative after deprotection of 5,6-diisopropylidene functionality can be easily converted to epoxide, which can also be stereoselectively opened with an azide anion to form C-4 axial azide. C-6 mesylation of azide, followed by its reduction with sodium borohydride/nickel chloride produces methyl 2-amino-4-acetamidogulopyranoside. 

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