Corey-Mukaiyama method

Recently, Corey and coworkers prepared the cinchonidine-derived bifluoride 20 from the corresponding bromide by passage of a methanolic solution through a column of Amberlyst A-26 OH- form, and subsequent neutralization with 2 equiv. of 1 N HF solution and evaporation (the modified method C in Scheme 9.5). The catalytic activity and chiral efficiency of 20 (dried over P205 under vacuum) have been demonstrated by the development of a Mukaiyama-type aldol reaction of ketene silyl acetal 21 with aldehydes under mild conditions, giving mostly syw-P-hydroxy-a-amino esters 22 as the major diastereomer with good to excellent enantiomeric excesses (Table 9.4) [23],... 

Method 2. Corey s double activation method for lactone formation is patterned after Mukaiyama s procedure for peptide formation and involves refluxing a solution of the 2-pyridinethiol ester of a hydroxy acid in a high-boiling solvent for a prolonged period of time.6... 

In 1976, Mukaiyama et al. [21] developed an efficient macrocyclization method mediated by l-methyl-2-chloropyridinium iodide (28). As shown in Scheme 10, the mechanism of this method is similar to that of Corey. It was found that triethylamine is the most suitable base and optimal yields were obtained in refluxing acetonitrile or dichloromethane. 

In fact, many methods discussed above, such as that of Corey and Mukaiyama, in the final analysis, fall into the activated ester class. Several other real activated ester methods are given below. 

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