Active catalyst asymmetric closure

Synthesis of Optically Active Epoxides. Alkaloids and alkaloid salts have been successfully used as catalysts for the asymmetric synthesis of epoxides. The use of chiral catalysts such as quinine or quinium benzylchloride (QUIBEC) have allowed access to optically active epoxides through a variety of reaction conditions, including oxidation using Hydrogen Peroxide (eq 5), Darzens condensations (eq 6), epoxidation of ketones by Sodium Hypochlorite (eq 7), halohydrin ring closure (eq 8), and cyanide addition to a-halo ketones (eq 9). Although the relative stereochemistry of most of the products has not been determined, enan-tiomerically enriched materials have been isolated. A more recent example has been published in which optically active 2,3-epoxycyclohexanone has been synthesized by oxidation with t-Butyl Hydroperoxide in the presence of QUIBEC and the absolute stereochemistry of the product established (eq 10). ... 

The asymmetric synthesis of cyclopropanes has attracted continual efforts in organic synthesis, due to their relevance in natural products and biologically active compounds. The prevalent methods employed include halomethylmetal mediated processes in the presence of chiral auxiliaries/catalysts (Simmons-Smith-type reactions), transition-metal-catalyzed decomposition of diazoalkanes, Michael-induced ring closures, or asymmetric metalations [8-10,46], However, the asymmetric preparation of unfunctionahzed cyclopropanes remains relatively undisclosed. The enantioselective activation of unactivated C-H bonds via transition-metal catalysis is an area of active research in organic chemistry [47-49]. Recently, a few groups investigated the enantioselective synthesis of cyclopropanes by direct functionalization reactions. 

The first catalytic, asymmetric synthesis of /3-lactams from ketenes and imines with useful selectivity was reported by Lectka, who used cinchona alkaloids [99]. The underlying principle in the development of such processes is the recognition that the optically active amine catalyst undergoes addition to the ketene to provide a chiral enolate, which then adds to the imine. The intermediate chiral zwitterion undergoes ring-closure, producing the /3-lac-tam. The cinchona alkaloid 111 has served admirably as a nucleophilic amine catalyst, furnishing adducts such as 112 with excellent enantio- and diastereoselectivity (99 1 dr, 99% ee, Equation 8) [31, 32, 99, 100]. 

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