Mesyl with cesium propionate

SN2-Suhf.titutions. The configuration of secondary alcohols can be inverted by reaction of the mesylate with cesium propionate (65-100% yield). The reagent reacts with secondary alkyl halides to form the ester of the inverted alcohol (85 100% yield). Some elimination occurs in reaction of the mesylates of menthol and cholestanol. ... 

Alcohol inversion. Elimination competes with S, 2 substitution in the inversion of secondary alcohols by the Mitsunobu reaction or by reaction of mesylates with cesium propionate or cesium acetate. Elimination in the inversion of cyclopentyl and cyclohexyl alcohols can be largely suppressed by reaction of the mesylate with cesium acetate (excess) and a catalytic amount of l8-crown-6 in refluxing benzene. Even inversion of an ally lie alcohol can be effected in moderate yield under these conditions (equation I). ... 

The properties of cesium salts can be taken advantage of to convert (5)-ethyl lactate to its / -enantiomer without racemization [63]. Treatment of mesylate 156b with cesium propionate gives (7 )-(acyloxy)propionate (170) in good yield [72]. Titanium-mediated transesterification of the ( S)-enantiomer of 170 under essentially neutral conditions has been reported to give ethyl L-lactate (60% yield) with no racemization [64]. Application of this methodology to (/ )-170 should give ethyl D-lactate (171). 

A new epoxide inversion method has been developed which uses cesium propionate as a key reagent to promote nucleophilic ring opening, initially providing a mixture of regio-isomeric hydroxyesters (e.g. 70 71). Subsequent mesylation of the hydroxylic groups in the crude reaction mixture, followed by treatment with potassium carbonate, provides the inverted epoxide (R.K-69) <02TL4111 >. 

Inversion of Chiral Alcohols. One of the most common applications for cesium acetate is its use in the inversion of the stereochemistry of secondary alcohols that have been converted into better leaving groups. Once the acetate is substituted via a direct SN2-fike displacement, it can then be easily converted back to the alcohol. Some attribute the enhanced nucleophilicity of cesium acetate to a cesium effect. Previously, cesium propionate had been used with alkyl mesylates. The use of this reagent generally resulted in good yields and was preferred to other methods, but it could lead to complicated interpretation of resulting H NMR spectra, whereas an acetate product could be more easily carried forward into further synthetic modification. 

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