174004-08-1Relevant academic research and scientific papers
London Dispersion Interactions Rather than Steric Hindrance Determine the Enantioselectivity of the Corey–Bakshi–Shibata Reduction
Eschmann, Christian,Song, Lijuan,Schreiner, Peter R.
supporting information, p. 4823 - 4832 (2021/02/01)
The well-known Corey–Bakshi–Shibata (CBS) reduction is a powerful method for the asymmetric synthesis of alcohols from prochiral ketones, often featuring high yields and excellent selectivities. While steric repulsion has been regarded as the key director of the observed high enantioselectivity for many years, we show that London dispersion (LD) interactions are at least as important for enantiodiscrimination. We exemplify this through a combination of detailed computational and experimental studies for a series of modified CBS catalysts equipped with dispersion energy donors (DEDs) in the catalysts and the substrates. Our results demonstrate that attractive LD interactions between the catalyst and the substrate, rather than steric repulsion, determine the selectivity. As a key outcome of our study, we were able to improve the catalyst design for some challenging CBS reductions.
Efficient Access to Chiral Benzhydrols via Asymmetric Transfer Hydrogenation of Unsymmetrical Benzophenones with Bifunctional Oxo-Tethered Ruthenium Catalysts
Touge, Taichiro,Nara, Hideki,Fujiwhara, Mitsuhiko,Kayaki, Yoshihito,Ikariya, Takao
supporting information, p. 10084 - 10087 (2016/09/03)
A concise asymmetric transfer hydrogenation of diaryl ketones, promoted by bifunctional Ru complexes with an etherial linkage between 1,2-diphenylethylenediamine (DPEN) and η6-arene ligands, was successfully developed. Because of the effective discrimination of substituents at the ortho position on the aryl group, unsymmetrical benzophenones were smoothly reduced in a 5:2 mixture of formic acid and triethylamine with an unprecedented level of excellent enantioselectivity. For the non-ortho-substituted benzophenones, the oxo-tethered catalyst electronically discerned biased substrates, resulting in attractive performance yielding chiral diarylmethanols with >99% ee.
Catalytic enantioselective aryl transfer to aldehydes using chiral 2,2'-bispyrrolidine-based salan ligands
Jia, Xuefeng,Lin, Aijun,Mao, Zhijie,Zhu, Chengjian,Cheng, Yixiang
experimental part, p. 2971 - 2981 (2011/05/19)
Chiral C2-symmetric diamines have emerged as versatile auxiliaries or ligands in numerous asymmetric transformations. Chiral 2,2'-bispyrrolidine-based salan ligands were prepared and applied to the asymmetric aryl transfer to aldehydes with arylboronic acids as the source of transferable aryl groups. The corresponding diarylmethanols were obtained in high yields with moderate to good enantioselectivitives of up to 83% ee.
Novel Electronic Effects of Remote Substituents on the Oxazaborolidene Catalyzed Enantioselective Reduction of Ketones
Corey, E. J.,Helal, Christopher J.
, p. 9153 - 9156 (2007/10/02)
A new class of hihgly enantioselective oxazaborolidine-catalyzed reductions of achiral ketones is reported which depends on steroelectronic effects involving p-substituted non-planar aromatic ketones, or ?-coordinated transition-metal containing ketones, or strained ring ketones, as exemplified in Table 1.The discovery of these reactions was guided by the transition state model 1, for which they provide experimental support.Because high enentioselectivities (>30:1) are achievable, these reductions define an excellent method for the synthesis of, for example, chiral benzhydrols, chiral propargylic, or chiral allylic alcohols.Lower enantioselectivities observed with CH2Cl2 as solvent, relative to toluene as solvent, are consistent with the transition-state model 1 and indicate that CH2Cl2 hydrogen bonds to the donor groups in the ?-electron-rich carbonyl substituent (RL in 1) thereby diminishing electron supply.
