139014-53-2Relevant articles and documents
Zirconium-Salan Catalyzed Enantioselective α-Hydroxylation of β-Keto Esters
Chen, Jie,Gu, Haiyang,Zhu, Xueying,Nam, Wonwoo,Wang, Bin
supporting information, p. 2976 - 2983 (2020/07/06)
We report herein the development of enantioselective and scalable α-hydroxylation of 1-indanone-derived β-keto esters by Zr(IV) complexes bearing readily available C2-symmetric salan ligands and cumene hydroperoxide as an oxidant, affording synthetically valuable hydroxylation products in high yields (up to 99percent) with excellent enantioselectivities (up to 99percent ee) under mild reaction conditions. In mechanistic studies, we have shown that (1) a Zr(IV)-salan complex was generated in situ as the active catalyst responsible for the chiral induction, (2) the transfer of the electrophilic fragment from cumene hydroperoxide to the Zr(IV)-bound enolate was accompanied by a heterolytic O?O bond cleavage, and (3) the formation of hydrogen bond between the amine hydrogen atom(s) of the salan ligand and the hydroxy group of cumene hydroperoxide was significant for stabilizing the stereocontrolled transition state and improving the enantioselectivity. (Figure presented.).
Group 4 metal complexes with new chiral pincer NHC-ligands: Synthesis, structure and catalytic activity
Zhao, Ning,Hou, Guohua,Deng, Xuebin,Zi, Guofu,Walter, Marc D.
, p. 8261 - 8272 (2014/06/09)
Chiral group 4 NHC-metal complexes were prepared in good yields by amine elimination from M(NR2)4 (M = Ti, Zr, Hf; R = Me, Et) and chiral pincer NHC-ligands, L4 (L4a and L4b), L5 and L6, which are derived from (S,S)-diphenyl-1,2-ethanediamine. Treatment of M(NR2)4 with 1 equiv. of L4 in THF gives, after recrystallization from a benzene solution, the chiral titanium amides (L4)Ti(NMe2)(Br)(THF) (7) and (L4)Ti(NMe2)(Cl)(THF) (11), zirconium amides (L4)Zr(NMe 2)(Br)(THF) (8), (L4)Zr(NEt2)(Br)(THF) (10), (L4)Zr(NMe2)(Cl)(THF) (12) and (L4)Zr(NEt2)(Cl)(THF) (14), and hafnium amides (L4)Hf(NMe2)(Br)(THF) (9) and (L4)Hf(NMe 2)(Cl)(THF) (13), respectively. Similarly, the reactions of L5 or L6 with 1 equiv. of M(NR2)4 yield the titanium amide (L6)Ti(NMe2)(Cl)(THF) (16), the zirconium amides (L5)Zr(NMe 2)(Cl)(THF) (15), (L6)Zr(NMe2)(Cl)(THF) (17) and (L6)Zr(NEt2)(Cl)(THF) (19), and the hafnium amide (L6)Hf(NMe 2)(Cl)(THF) (18), respectively. Complexes 7-19 were characterized by various spectroscopic techniques and elemental analyses. The molecular structures of 10 and 14-19 were also established by X-ray diffraction analyses, which represent the first example of the structurally characterized group 4 chiral NHC-metal complex. Furthermore, 7-19 are active catalysts for the polymerization of rac-lactide in the presence of isopropanol, leading to the heterotactic-rich polylactides. the Partner Organisations 2014.
Highly enantioselective cyclopropanation of styrene derivatives using Co(III)-salen complex as a catalyst
Fukuda, Tsutomu,Katsuki, Tsutomu
, p. 7201 - 7208 (2007/10/03)
Optically active (salen)cobalt(III) bromide complex 6-Br was found to be an efficient catalyst for asymmetric cyclopropanation of styrene derivatives. For example, the reaction of 4-chlorostyrene and tert-butyl diazoacetate in the presence of 6-Br proceeded with high enantioselectivity of 96% ee as well as high trans-cis selectivity (97:3) to give tert-butyl 2-(4-chlorophenyl)cyclopropane-1-carboxylate as a major product.
