title: DOSY NMR for monitoring self aggregation of bifunctional organocatalysts: increasing enantioselectivity with decreasing catalyst concentration.
abstract: 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.
authors.affiliation: Department of Chemistry, Sungkyunkwan University, 300 Cheoncheon, Jangan, Suwon, Gyeonggi 440-746, Korea.
authors.forename: Hyeong Bin
authors.initials: HB
authors.lastname: Jang
authors.forename: Ho Sik
authors.initials: HS
authors.lastname: Rho
authors.forename: Joong Suk
authors.initials: JS
authors.lastname: Oh
authors.forename: Eun Hye
authors.initials: EH
authors.lastname: Nam
authors.forename: Sang Eun
authors.initials: SE
authors.lastname: Park
authors.forename: Han Yong
authors.initials: HY
authors.lastname: Bae
authors.forename: Choong Eui
authors.initials: CE
authors.lastname: Song
mesh_terms: D002384:Catalysis; D004058:Diffusion; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D015394:Molecular Structure; D055601:Organic Chemistry Phenomena; D013237:Stereoisomerism