Kai Lang

Publications of Kai Lang

• Urea/transition-metal cooperative catalyst for anti-selective asymmetric nitroaldol reactions.

  Authors: Kai Lang, Jongwoo Park, Sukwon Hong

  Angewandte Chemie (International ed. in English). 02/2012; 51(7):1620-4.

  A cooperative catalyst that features urea H-bonding and a cobalt center was developed for anti-selective asymmetric Henry reactions. The H-bonds of urea play a crucial role in the improvement inA cooperative catalyst that features urea H-bonding and a cobalt center was developed for anti-selective asymmetric Henry reactions. The H-bonds of urea play a crucial role in the improvement in yield (from 30 % to 84 %), enantioselectivity (from 78 % to 96 %), and anti diastereoselectivity (from 3:1 to 48:1). A short synthesis of (1R,2S)-methoxamine hydrochloride was also accomplished with this catalyst.

• Self-assembly approach toward chiral bimetallic catalysts: bis-urea-functionalized (salen)cobalt complexes for the hydrolytic kinetic resolution of epoxides.

  Authors: Jongwoo Park, Kai Lang, Khalil A Abboud, Sukwon Hong

  Chemistry (Weinheim an der Bergstrasse, Germany). 02/2011; 17(7):2236-45.

  A series of novel bis-urea-functionalized (salen)Co complexes has been developed. The complexes were designed to form self-assembled structures in solution through intermolecular urea-ureaA series of novel bis-urea-functionalized (salen)Co complexes has been developed. The complexes were designed to form self-assembled structures in solution through intermolecular urea-urea hydrogen-bonding interactions. These bis-urea (salen)Co catalysts resulted in rate acceleration (up to 13 times) in the hydrolytic kinetic resolution (HKR) of rac-epichlorohydrin in THF by facilitating cooperative activation, compared to the monomeric catalyst. In addition, one of the bis-urea (salen)Co(III) catalyst efficiently resolves various terminal epoxides even under solvent-free conditions by requiring much shorter reaction time at low catalyst loading (0.03-0.05 mol %). A series of kinetic/mechanistic studies demonstrated that the self-association of two (salen)Co units through urea-urea hydrogen bonds was responsible for the observed rate acceleration. The self-assembly study with the bis-urea (salen)Co by FTIR spectroscopy and with the corresponding (salen)Ni complex by (1)H NMR spectroscopy showed that intermolecular hydrogen-bonding interactions exist between the bis-urea scaffolds in THF. This result demonstrates that self-assembly approach by using non-covalent interactions can be an alternative and useful strategy toward the efficient HKR catalysis.

• Development of bifunctional aza-bis(oxazoline) copper catalysts for enantioselective Henry reaction.

  Authors: Kai Lang, Jongwoo Park, Sukwon Hong

  The Journal of organic chemistry. 10/2010; 75(19):6424-35.

  Base-functionalized aza-bis(oxazoline) ligands were prepared to explore the concept of dual activation through the Lewis acid and a tethered tertiary amine base. The catalytic activity of the CuBase-functionalized aza-bis(oxazoline) ligands were prepared to explore the concept of dual activation through the Lewis acid and a tethered tertiary amine base. The catalytic activity of the Cu complex was evaluated for the asymmetric Henry reaction. Compared with a corresponding unfunctionalized copper complex with external 1-benzyl-4-ethylpiperazine base, the ethylpiperazine-functionalized aza-bis(oxazoline) copper catalyst resulted in rate acceleration (2.5 times) as well as improved enantioselectivity (72% ee vs 92% ee).

• Self-assembled dinuclear cobalt(II)-salen catalyst through hydrogen-bonding and its application to enantioselective nitro-aldol (Henry) reaction.

  Authors: Jongwoo Park, Kai Lang, Khalil A Abboud, Sukwon Hong

  Journal of the American Chemical Society. 01/2009; 130(49):16484-5.

• Cyclization of samarium diiodide-generated vinyl radicals in 6-(pi-exo)-exo-dig mode.

  Authors: Zhuang-Ping Zhan, Kai Lang

  Organic & biomolecular chemistry. 04/2005; 3(5):727-8.

  Radical cyclization of vinyl iodides in 6-(pi-exo)-exo-dig mode were effected by SmI2 to give exo-cyclic dienes fused to six-membered rings.