Asymmetric catalysis with self‐organized chiral lanthanum complexes: Practical and highly enantioselective epoxidation of α,β‐unsaturated ketones

Abstract

A highly efficient and practical method for obtaining alpha,beta-epoxy ketones with high optical purities was developed. The chiral lanthanum complex self-organized in situ from lanthanum triisopropoxide, (R)-BINOL, triarylphosphine oxide, and alkyl hydroperoxide (1:1:1:1) was found to catalyze the epoxidation of alpha,beta-unsaturated ketones with tert-butyl hydroperoxide or cumene hydroperoxide at room temperature to give the corresponding epoxy ketones in high enantioselectivities (up to >99% enantiomeric excess (ee)). A remarkably high asymmetric amplification, a positive nonlinear effect, was observed in the epoxidation of chalcone, which strongly suggests the formation of a dinuclear peroxide-involved mu-complex as the active catalyst.

Dimeric samarium(III) alkoxides bearing N2O2 tetradentate Schiff bases and their utility for the catalytic epoxidation of trans-chalcone

“…These results are in good agreement with those reported using La(O i Pr) 3 /(R)-BINOL/Ph 3 PO as the catalytically active species [14]. Initial attempts at the catalytic epoxidation of trans-chalcone under identical conditions without activated molecular sieves failed, perhaps through the formation of tetranuclear clusters [1b].…”

“…One of the t-butyl groups is disordered with two preferred (30% and 70% occupancy) orientations about the C(21)-C(22) bond. (2) 13.027(7) b (Å ) 14.584 (2) 13.520(7) c (Å ) 18.441 (2) …”

Heterogenization of Shibasaki's Binol/La Catalyst for Enantioselective Epoxidation of α,β‐Unsaturated Ketones with Multitopic Binol Ligands: The Impact of Bridging Spacers

“…In the analogous homogeneous catalyst system, the employment of Ph 3 PO or Ph 3 AsO as additive in the reaction system dramatically enhanced the catalytic activity but scarcely influenced the enantioselectivity. [8,9] In contrast to the homogeneous catalytic system, the addition of triphenylphosphine oxide to the heterogeneous catalytic system described herein had a significant impact on both the activity and enantioselectivity of the catalysis ( We then turned our attention to investigating the impact of the bridging spacers in the multitopic ligands on the enantioselectivity of the catalysis under the optimized reaction conditions. The heterogeneous catalysts 2 b-i, generated from the reactions of multitopic ligands 1 b-i and La(OiPr) 3 , were subsequently applied to the epoxidation of 3 a with CMHP as the oxidant in the presence of Ph 3 PO (15 mol %) and MS (4 ).…”

“…Therefore, the design and synthesis of multitopic chiral ligands with diverse geometrical features is a central issue in the generation of homochiral metal-organic polymers for heterogeneous asymmetric catalysis (Figure 1). The homogeneous catalytic asymmetric epoxidation of a,b-unsaturated ketones in the presence of Shibasakis lanthanum catalyst, [8][9][10] which is based on the 2,2'-dihydroxy-1,1'-binaphthyl (binol) ligand, has provided one of the most convenient approaches to a,b-epoxy ketones among various catalytic systems developed so far. [11][12][13][14][15] Although excellent yields and enantioselectivity have been achieved, a catalyst loading of 5-20 mol % rendered the process less practical.…”

Recent developments in enantioselective lanthanide-catalyzed transformations

“…This protocol [60] was based on the use of La(Oi-Pr) 3 /BINOL/PPh 3 (O) complex as catalyst system and TBHP as oxidant in THF at room temperature. When using (R)-BINOL as ligand, the process led to chiral epoxide (3S,4R)-93 in 90% yield and 97% ee, while the employment of (S)-BINOL as ligand provided (3R,4S)-93 in 88% yield and 97% ee (Scheme 34).…”