Ivanov reaction carboxylic acid dianions

A completely different dipolar cycloaddition model has been proposed39 in order to rationalize the stereochemical outcome of the addition of doubly deprotonated carboxylic acids to aldehydes, which is known as the Ivanov reaction. In the irreversible reaction of phenylacetic acid with 2,2-dimethylpropanal, metal chelation is completely unfavorable. Thus simple diastereoselectivity in favor of u f/-adducts is extremely low when chelating cations, e.g., Zn2 + or Mg- +, are used. Amazingly, the most naked dianions provide the highest anti/syn ratios as indicated by the results obtained with the potassium salt in the presence of a crown ether. 

The Ivanov reaction is the preparation of a 3-hydroxy acid by reaction of the magnesium dianion of a carboxylic acid with an aldehyde or ketone." In a seminal paper, Zimmerman and Traxler investigated the Ivanov reaction of phenylacetic acid and benzaldehyde and obtained anti and syn 3-hydroxy acids (127) and (128) in 69% and 22% yields, respectively (equation 85). The observed stereochemistry was rationalized with a cyclic, chair-like transition state in which a magnesium cation is chelated by one oxygen each of the carboxylate enolate and the aldehyde (the Zimmerman-Traxler transition state ). 

The reactions of aldehydes with carboxylate enolates are stereochemical-ly related to the Ivanov reaction (dianions of arylacetic acids -t carbonyl compounds), named after the Bulgarian chemist Dimitar Ivanov Popov (1894-1975). 

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