Hydroxyl groups alcohols and phenols

The most commonly used reagents for the resolution of racemic alcohols are chiral acids, isocyanates and chloro- 

Esters are normally prepared from an alcohol and an activated chiral carboxylic acid, usually in the form of a chloride, anhydride, or imidazole. 

Acid chlorides are the most reactive, and are particularly useful for sterically hindered compounds or those which are difficult to acylate. However, care should be exercised when using these reagents, because certain acid chlorides, particularly those containing a proton attached to the chiral carbon, can racemize under extreme acidic or basic conditions or at elevated temperatures. The stability of these reagents should also be investigated to optimize storage and reaction conditions. 

Pew examples of derivatizations with other activated forms of the carboxylic acids were noted, but since these can readily be formed from the chiral acid they are worthy of further investigation and may offer several advantages over acid chlorides. 

The formation of diastereomeric esters using dicyclo-hexylcarbodiimide as a coupling reagent was used by Banfield and Rowland [20] in a quantitative assay for warfarin in biological fluids. 

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Protection of hydroxyl groups. Alcohols and phenols react with 1 and tri-ethylamine to form tetrahydro-2-furanyl (THF) ethers (85-98% yield). The reaction of acids with 1 results in THF esters. These derivatives are stable to base and nucleophilic reagents they are readily removed by acid-catalyzed hydrolysis or methanolysis. One synthetic application is conversion of the ethers into alkyl bromides by reaction with triphenyphosphine dibromide (1,1247-1248), a reaction that is faster than that with the free alcohols. 

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