Enantioselective Enolate Protonation: Matching Chiral Aniline and Substrate Acidity
摘要:
A comparison of chiral anilines 1a-f in the asymmetric protonation of enolate 15 shows that the optimum Delta pK(a) value (chiral acid vs protonated enolate) for the highest enantioselectivity is ca. 3 (Table 2). An extension of this concept to amino acid enolates was possible, and le was found to give the best enantioselectivity (85% ee) with the alanine-derived N-lithioenolate 5a (Table 3). Changes in aniline pK(a) due to variation of substituents at the aniline nitrogen were evaluated briefly, but these changes did not show consistent trends in the enantioselectivity vs pK(a).
Enantioselective Benzoylation of α-Amino Esters Using (<i>S</i>)-1-Benzoyl-2- (α-acetoxyethyl)benzimidazole, a Chiral Benzimidazolide
作者:Anil V. Karnik、Suchitra S. Kamath
DOI:10.1021/jo070962p
日期:2007.9.1
[GRAPHICS]A new chiral benzimidazolide is developed as a nonenzymatic acylating agent for enantioselective benzoylation of racemic cc-amino esters. The process is highly efficient, which exhibits uniformly high enantioselectivity for alpha-amino esters with or without aryl substituents under mild reaction conditions. The chiral benzimidazolide is inexpensive and is easily accessible.