DOSY NMR for monitoring self aggregation of bifunctional organocatalysts: increasing enantioselectivity with decreasing catalyst concentration

作者：Jang Hyeong Bin; Rho Ho Sik; Oh Joong Suk; Nam Eun Hye; Park Sang Eun; Bae Han Yong; Song Choong Eui^*

来源：Organic and Biomolecular Chemistry, 2010, 8(17): 3918-3922.

DOI：10.1039/c0Ob00047g

In this report, we demonstrate that self-aggregation is an intrinsic problem of bifunctional organocatalysts, especially in the case when the substrates do not have functional groups which are able to bind strongly with catalyst. Due to their self-association phenomena, the enantioselectivity of bifunctional catalysts dramatically decreases with increasing catalyst concentration or decreasing temperature. Thus, when the substrate concentration is kept constant, the enantioselectivity of bifunctional catalysts dramatically increases with decreasing catalyst loading. The ee values obtained at different catalyst concentrations are fairly consistent with the diffusion coefficients (D) of the catalysts, strongly indicating that their degree of self-association plays a crucial role in determining their enantioselectivity.

• 出版日期2010