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Stereochemistry of Alkylation of Carboxylic Acid Salt and Ester α Anions Derived from Cyclic Systems.
Krapcho, A.Paul,Dundulis, Edward A.
, p. 3236 - 3245 (2007/10/02)
A stereochemical study of the alkylation of α-lithiated carboxylate salts and esters has been performed.The α anions derived from the bicyclic acids exo-1, endo-1, and 7 (R=H) and the esters 4 and 7 (R=CH3) yield predominantly exo alkylation.As an example, the α anion derived from ester 7 (R=CH3) on treatment with CH3I yields exo-8 (R=R'=CH3) and endo-9 (R=R'=CH3) in a 97:3 ratio, a highly stereoselective reaction.Addition of TMEDA to the reactions involving the α anions derived from exo- or endo-1 did not change the stereochemical alkylation results.The α anions derived from the substituted cyclohexanecarboxylic acids 10, 13, 16, 19, or 22 (where R=H in each case) on methylation yield more axial methylation (axial/equatorial ratios of 0.4-2.7) than the α anions derived from the methyl esters corresponding to these acids.The α anions from the esters yield predominantly equatorial methylated products (e/a ratios varying from 4 to 9).The reasons for the different stereochemical results are discussed.
