Enantioselective 6-exo-Bromoaminocyclization of Homoallylic N-Tosylcarbamates Catalyzed by a Novel Monophosphine-Sc(OTf)3 Complex

The applications of catalytic asymmetric halocyclization in natural product synthesis

Catalytic asymmetric halocyclization of olefinic substrate has evolved rapidly and been well utilized as a practical strategy for constructing enantioenriched cyclic skeletons in natural product synthesis.

Chiral oxamide–phosphine–palladium catalyzed highly asymmetric allylic amination: carbonyl assistance for high regio- and enantiocontrols

The chiral oxamide–phosphine (COAP) ligands were developed for the palladium-catalyzed asymmetric allylic amination of vinyl benzoxazinones with alkylamines, affording a series of optically active diamines in good yields with high enantioselectivity.

Catalytic enantioselective bromohydroxylation of cinnamyl alcohols

This work describes an effective enantioselective bromohydroxylation of cinnamyl alcohols with (DHQD)₂PHAL as the catalyst and H₂O as the nucleophile, providing a variety of corresponding optically active bromohydrins with up to 95% ee.

Optically active bromohydrins are obtained with up to 95% ee via asymmetric bromohydroxylation of cinnamyl alcohols with H₂O as nucleophile.

Ritter-enabled catalytic asymmetric chloroamidation of olefins

Intermolecular asymmetric haloamination reactions are challenging due to the inherently high halenium affinity (HalA) of the nitrogen atom, which often leads to N-halogenated products as a kinetic trap. To circumvent this issue, acetonitrile, possessing a low HalA, was used as the nucleophile in the catalytic asymmetric Ritter-type chloroamidation of allyl-amides. This method is compatible with Z and E alkenes with both alkyl and aromatic substitution. Mild acidic workup reveals the 1,2-chloroamide products with enantiomeric excess greater than 95% for many examples. We also report the successful use of the sulfonamide chlorenium reagent dichloramine-T in this chlorenium-initiated catalytic asymmetric Ritter-type reaction. Facile modifications lead to chiral imidazoline, guanidine, and orthogonally protected 1,2,3 chiral tri-amines.

Intermolecular haloamination reactions are challenging due to the high halenium affinity of the nitrogen atom. This is circumvented by using acetonitrile as an attenuated nucleophile, resulting in an enantioselective halo-Ritter reaction.

Catalytic, Enantioselective Synthesis of Cyclic Carbamates from Dialkyl Amines by CO2-Capture: Discovery, Development, and Mechanism

Cyclic carbamates are a common feature of small-molecule therapeutics, offering a constrained hydrogen bond acceptor that is both polar and sterically small. Methods for their preparation most often focus first on amino alcohol synthesis and then reaction with phosgene or its equivalent. This report describes an enantioselective synthesis of cyclic carbamates in which carbon dioxide engages an unsaturated basic amine, facilitated by a bifunctional organocatalyst designed to stabilize a carbamic acid intermediate while activating it toward subsequent enantioselective carbon-oxygen bond formation. Six-membered cyclic carbamates are prepared in good yield with high levels of enantioselection, as constrained 1,3-amino alcohols featuring a chiral tertiary alcohol carbon. Spectroscopic analysis (NMR, DOSY) of various substrate-reagent combinations provides insight into the dominant species under the reaction conditions. Two peculiar requirements were identified to achieve highest consistency: a "Goldilocks" amount of water and the use of a noncrystalline form of the ligand. These atypical features of the final protocol notwithstanding, a diverse range of products could be prepared. Their functionalizations illustrate the versatility of the carbamates as precursors to enantioenriched small molecules.

Asymmetric Catalytic Halofunctionalization of α,β-Unsaturated Carbonyl Compounds

Halofunctionalization methods enable the vicinal difunctionalization of alkenes with heteroatom nucleophiles and halogen moieties. As a fundamental transformation in organic synthesis, the catalytic asymmetric variants have only recently been reported. In sharp contrast to the asymmetric halocyclization of simple alkenes which involves a nucleophile-assisted alkene activation process, the asymmetric halofunctionalization of enones developed by our laboratory features an electrophile-assisted 1,4-addition pathway. Our work in this area has resulted in the development of several different types of regio-, diastereo-, and enantioselective processes, including inter- and intramolecular haloaminations, haloetherifications, and haloazidations. The scope, updated mechanism, limitations, and future perspective of these reactions are discussed.

Enantioselective Halolactonization Reactions using BINOL-Derived Bifunctional Catalysts: Methodology, Diversification, and Applications

A general protocol is described for inducing enantioselective halolactonizations of unsaturated carboxylic acids using novel bifunctional organic catalysts derived from a chiral binaphthalene scaffold. Bromo- and iodolactonization reactions of diversely substituted, unsaturated carboxylic acids proceed with high degrees of enantioselectivity, regioselectivity, and diastereoselectivity. Notably, these BINOL-derived catalysts are the first to induce the bromo- and iodolactonizations of 5-alkyl-4( Z)-olefinic acids via 5- exo mode cyclizations to give lactones in which new carbon-halogen bonds are created at a stereogenic center with high diastereo- and enantioselectivities. Iodolactonizations of 6-substituted-5( Z)-olefinic acids also occur via 6- exo cyclizations to provide δ-lactones with excellent enantioselectivities. Several notable applications of this halolactonization methodology were developed for desymmetrization, kinetic resolution, and epoxidation of Z-alkenes. The utility of these reactions is demonstrated by their application to a synthesis of precursors of the F-ring subunit of kibdelone C and to the shortest catalytic, enantioselective synthesis of (+)-disparlure reported to date.

Copper Promoted Regio- and Stereoselective Aminochlorination of Alkynes and Alkenes with NFSI

A simple and rapid copper-promoted aminochlorination of unactivated alkynes and alkenes with N-fluorobenzenesulfonimide (NFSI) was developed. Two series of chloroenamines and chloroamines were obtained in good to high yields. The chlorinated enamines could be obtained in a single E configuration. This reaction involved a radical process and the CuCl₂ acted as the Cl source and NFSI as the N source.

Chiral N,N′-dioxide-Sc(NTf2)3 complex-catalyzed asymmetric bromoamination of chalones with N-bromosuccinimide as both bromine and amide source

A chiral N,N′-dioxide-Sc(NTf₂)₃ complex catalytic system has been developed to catalyze the asymmetric bromoamination reaction of chalones with N-bromosuccinimide.

Phosphine Oxide-Sc(OTf)3 Catalyzed Highly Regio- and Enantioselective Bromoaminocyclization of (E)-Cinnamyl Tosylcarbamates. An Approach to a Class of Synthetically Versatile Functionalized Molecules

A highly regio- and enantioselective bromoaminocyclization of (E)-cinnamyl tosylcarbamates catalyzed by a chiral phosphine oxide-Sc(OTf)3 complex is described. A wide variety of optically active aryl 5-bromo-1,3-oxazinan-2-ones can be obtained with high yield and enantioselectivity.

Visible-light-promoted chloramination of olefins with N-chlorosulfonamide as both nitrogen and chlorine sources

A visible-light-promoted chloramination of olefins is reported.