Mechanism and Conditions for Highly Enantioselective Epoxidation of α,β-Enones Using Charge-Accelerated Catalysis by a Rigid Quaternary Ammonium Salt

Abstract

[formula: see text] Highly enantioselective (up to 130:1) epoxidation of a variety of alpha,beta-enones to form alpha,beta-epoxy ketones is described along with a rational analysis of the mechanistic basis for this strong absolute stereochemical control by the chiral catalyst 2.

Total Synthesis of Leukotrienes from Butadiene

“…The use of Pd/C gave lower yields due to epoxide opening. [45] Cleavage of the acetate under the same conditions as described for 17, with a catalytic amount of K 2 CO 3 in the presence of anhydrous Na 2 SO 4 in MeOH, gave the crystalline epoxy alcohol 21 in 69% yield after recrystallization from pentane; this compound was identical to a sample prepared from (E)-2-octen-1-ol by Sharpless epoxidation. [46] Oxidation with Py 2 ·CrO 3 in CH 2 Cl 2 gave the epoxy aldehyde 22 (63% isolated yield).…”

Enantioselective Organocatalysis

“…[161] Likewise, faceselective conjugate additions of ion-paired hypochlorite to an a,b-enone have been realized by using 46 e (X Br) as catalyst. [162] The reaction affords the corresponding epoxide with a remarkably good (up to 130:1) enantioselectivity.…”

Asymmetric Epoxidation in Stereoselective Synthesis

“…Their work also provided a practical process for the transformation of the resulting epoxy ketones into highly useful organic intermediates, including a-hydroxyl ketones, b-hydroxyl ketones, and a,b-epoxy esters (Scheme 35.29). 73 Lygo and co-workers used an asymmetric phasetransfer-catalyzed epoxidation in the stereoselective synthesis of loxistatin, a potent and selective cysteine protease inhibitor (Scheme 35.30). The diastereoselective epoxidation of the enone 108 bearing a leucine ester moiety using 105 as phase-transfer catalyst provided epoxide 109 in good yield.…”