Diastereoselective acyclic carboxylic acids

Diastereoselective Adulations of Acyclic Carboxylic Acid Derivatives Containing Chiral Auxiliary Groups... 

For acyclic systems, the anti diastereoselectivity of the (i )-enolates is lower than the syn diastereoselectivity of comparable (Z)-enolates. For example, carboxylic acid esters, which form predominantly ( )-enolates, react with aldehydes with high anti selectivity only in those cases where bulky aromatic substituents are in the alcoholic part of the ester22 25. 

The (diastereoselective) conjugate addition of silylcuprate reagents to a variety of chiral derivatives of a,(3-unsaturated carboxylic acids can be used to prepare optically active p-silyl esters.258 259 Best results are obtained with substrates of type (25). The (related) p-silyl ketones, which also constitute valuable building blocks for (acyclic) stereoselective synthesis, are now accessible in high ee via palladium-catalyzed enantioselective 1,4-disiiylation of a,p-unsaturated ketones (Scheme 76).260... 

Diastereoselective Adulations of Acyclic Enoiates of Carboxylic Acid Derivatives... 

Use of 3-pyrrohdine carboxylic acids (7.139) and (7.140) as catalysts results in formation of the anft -Mannich adduct as the major product. This reversal in diastereoselectivity arises from reaction of the s-cis conformer of the enamine formed from (7.139) or (7.140), as depicted in Figure 7.6. Catalyst (7.139) provides high ees in the anfr-Mannich reaction of aliphatic cyclic and acyclic ketones such as pentan-3-one (7.141) while the methyl-substituted analogue (7.140) catalyses the anti-addition of a range of aliphatic aldehydes in 98 to >99%... 

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