18-Crown alcohol inversion

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). ... 

Inversion of a neopentylic hydroxyl group.1 Although SN2 reactions at a ncopentylic position proceed with difficulty, the alcohol 1 was epimerized by reaction of the mesylate with K02 and dibenzo-18-crown-6 in DMSO-DME in high yield. 

The reaction of primary alkyl bromides or sulfonate esters with potassium superoxide solubilized in benzene gives dialkyl peroxides, ROOR, as the major product. Significant amounts of alcohols and olefins are also formed. If the reaction is carried out in DMSO or DMSO-DMF, primary alcohols are formed very rapidly with inversion of configuration. Catalytic amounts of a crown ether are sufficient, but use of 1-2 eq. leads to a more rapid reaction. Secondary alcohols can be obtained, often in high yield, by this displacement reaction, but elimination predominates with tertiary substrates. This Sn2 reaction has been... 

Inversion of alcohols By chloromesylation (with ClCH2S02Cl/py), treatment with CsOAc/18-crown-6, and hydrolysis, a secondary alcohol is converted into its enantiomer. 

Crown-catalysed substitution by chromate ions provides a direct oxidation route from primary halides to aldehydes via chromate esters (39). Superoxide anion becomes a useful new type of oxygen nucleophile now that potassium superoxide can be solubilized with 18-crown-6 and derivatives. Alkyl halides or sulphonates (RX) may be converted to alcohols or dialkyl peroxides, depending on the exact conditions, through an initial nucleophilic substitution with inversion (Scheme 8). 

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