Asymmetric Epoxidation of Unsaturated Ketones Catalyzed by Heterobimetallic Rare Earth–Lithium Complexes Bearing Phenoxy-Functionalized Chiral Diphenylprolinolate Ligand

Abstract

Four novel heterobimetallic complexes [REL2]{[(THF)3Li]2(μ-Cl)} stabilized by chiral phenoxy-functionalized prolinolate (RE = Yb (1), Y (2), Sm (3), Nd (4), H2L = (S)-2,4-di-tert-butyl-6-[[2-(hydroxydiphenylmethyl)pyrrolidin-1-yl]methyl]phenol have been synthesized and characterized. These readily available complexes are highly active in catalyzing the epoxidation of α,β-unsaturated ketones, while the enantioselectivity varies according to the ionic radii of the rare earth center. A series of chalcone derivatives were converted to chiral epoxides in 80 → 99% ee at 0 °C using TBHP as the oxidant in the presence of 10 mol % of 1.

One Pot and Two Pot Synthetic Strategies and Biological Applications of Epoxy-Chalcones

“…α, α-diphenyl-Lprolinol) could cause some problems especially on the large amount of catalyst loading, requirements of additive reagents, long reaction time, additive and unproductive ee value. That one can controlled by using transition metal based catalysts [109].…”

Recent developments in enantioselective lanthanide-catalyzed transformations

“…In 2014, Zhao and Yao reported the synthesis of novel heterobimetallic complexes stabilized by chiral phenoxy-functionalized prolinolate, such as Yb/Li complex 96 [61]. As shown in Scheme 35, this catalyst was prepared by treating two equivalents of the corresponding ligand 97 with four equivalents of n-BuLi in THF, providing intermediate dilithium salt 98 which was subsequently treated with anhydrous YbCl 3 to give final heterobimetallic Yb/ Li/97 complex 96.…”

Highly Enantioselective Epoxidation of α,β-Unsaturated Ketones Catalyzed by Rare-Earth Amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with Phenoxy-Functionalized Chiral Prolinols

“…((2S, 3R)-3-phenyloxiran-2-yl)-phenylmethanone (7a) [5] A white powder; yield 99%, ee 98% ; ((2S, 3R)-3-phenyloxiran-2-yl)-p-tolylmethanone (7b) [5] A white powder; yield 98%, ee 96%; ((2S, 3R)-3-phenyloxiran-2-yl)-4-methoxyphenylmethanone (7c) [5] A white powder; yield 97%, ee 98%; (2-methoxyphenyl)((2S, 3R)-3-phenyloxiran-2-yl)methanone (7d) [6] A white powder; yield 91%, ee 96%; (naphthalen-3-yl)((2S, 3R)-3-phenyloxiran-2-yl)methanone (7e) [3] A white powder; yield 99%, ee 99%; (4-pentylphenyl)((2S, 3R)-3-phenyloxiran-2-yl)methanone (7f) [5] A white powder; yield 98%, ee 94%; [α] D 24 162 o (c 0.7 in acetone). 1 (4-chlorophenyl)((2S, 3R)-3-phenyloxiran-2-yl)methanone (7g) [5] A white powder; yield 99%, ee 94%; (4-bromophenyl)((2S, 3R)-3-phenyloxiran-2-yl)methanone (7h) [5] A white powder; yield 99%, ee 87%; (4-fluorophenyl)((2S, 3R)-3-phenyloxiran-2-yl)methanone (7i) [5] A white powder; yield 97%, ee 89%; [α] D 24 204 o (c 0.7 in acetone). 1…”

“…The ee values determination was carried out using HPLC (Agilent Technologies 1200 Series) with Daicel Chiralcel columns at 23-25 o C. Optical rotation was measured using an Autopol IV Polarimeter equipped with a sodium vapor lamp at 589 nm. The absolute configuration was determined by comparing the specific rotation with the literature data [1][2][3][4][5] . Hence, 7r, 7t, 7u, 7w were assigned by analogy, assuming a common reaction pathway.Suitable single crystal of complex 6 was sealed in a thin-walled glass capillary for determining the single-crystal structure.…”