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

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.

Acid-Mediated Decarboxylative C–H Coupling between Arenes and O-Allyl Carbamates

Treatment of O-allyl N-tosyl carbamates with aromatic compounds in the presence of Cu(OTf)2 or TMSOTf as promoters, affords N-substituted 1-arylpropan-2-amines, 1,2-diarylpropanes, 1,1-diarylpropanes, or indanes, depending on the nature of the...

Asymmetric Bromoaminocyclization and Desymmetrization of Cyclohexa-1,4-dienes through Anion Phase-Transfer Catalysis

The catalytic enantioselective desymmetrizing bromoaminocyclization of prochiral cyclohexa-1,4-dienes has been achieved by using chiral anion phase-transfer catalysis, providing a range of enantioenriched cis-3a-arylhydroindoles bearing an all-carbon quaternary stereocenter in good yields (up to 78%) and excellent enantioselectivities (up to 97% ee). Furthermore, the potential application of this methodology to natural product total synthesis was demonstrated by the asymmetric synthesis of (+)-Mesembrane.

Regio- and diastereoselective Pd-catalyzed aminochlorocyclization of allylic carbamates: scope, derivatization, and mechanism

The regio- and diastereoselective synthesis of oxazolidinones via a Pd-catalyzed vicinal C-N/C-Cl bond-forming reaction from internal alkenes of allylic carbamates is reported. The oxazolidinones are obtained in yields of 44 to 95% with high to excellent diastereoselectivities (from 6 : 1 to >20 : 1 dr) from readily available precursors. This process is scalable, and the products are suitable for the synthesis of useful amino alcohols. A detailed theoretical and experimental mechanistic study was carried out to describe that the reaction proceeds through an anti-aminopalladation of the alkene followed by an oxidative C-Pd(ii) cleavage with retention of the carbon stereochemistry to yield the major diastereomer. The role of Cu(ii) in a C-Cl bond-forming mechanism step has also been proposed.

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.

The Use of Domino Reactions for the Synthesis of Chiral Rings

This short review highlights the recent developments reported in the last four years on the asymmetric construction of chiral rings based on enantioselective domino reactions promoted by chiral metal catalysts.

1 Introduction

2 Formation of One Ring Containing One Nitrogen Atom

3 Formation of One Ring Containing One Oxygen/Sulfur Atom

4 Formation of One Ring Containing Several Heterocyclic Atoms

5 Formation of One Carbon Ring

6 Formation of Two Rings

7 Conclusion

Enantioselective Syntheses of 4H-3,1-Benzoxazines via Catalytic Asymmetric Chlorocyclization of o-Vinylanilides

The catalytic asymmetric halocyclization of alkene is a powerful and straightforward strategy for the synthesis of chiral heterocyclic compounds. Herein, an effective approach to chiral benzoxazine derivatives through organocatalyzed chlorocyclization of o-vinylanilides was reported. This method provides facile access to a series of chiral benzoxazines in good to excellent yields (up to 99% yield) and with high-level enantiocontrol (up to 92% ee).

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.

1,3-Dioxa-[3,3]-sigmatropic Oxo-Rearrangement of Substituted Allylic Carbamates: Scope and Mechanistic Studies

An unexpected 1,3-dioxa-[3,3]-sigmatropic rearrangement during the treatment of aryl- and alkenyl-substituted allylic alcohols with activated isocyanates is reported. The reorganization of bonds is highly dependent on the electron density of the aromatic ring and the nature of isocyanate used. This metal-free tandem reaction from branched allyl alcohols initiated by a carbamoylation reaction and followed by a sigmatropic rearrangement thus offers a new access to ( E)-cinnamyl and conjugated ( E, E)-diene carbamates, such as N-acyl and N-sulfonyl derivatives. A computational study was conducted in order to rationalize this phenomenon, and a rearrangement progress kinetic analysis was performed.

Enantioselective Bromolactonization of Trisubstituted Olefinic Acids Catalyzed by Chiral Pyridyl Phosphoramides

Enantioselective bromolactonization of trisubstituted olefinic acids producing synthetically useful chiral lactones with two contiguous asymmetric centers has remained mainly unexplored except for the 6-exo cyclization mode. In this work, the 5-exo- and 6-endo modes of bromocyclization of trisubstituted olefinic acids were enabled for the first time using N-bromosuccinimide and a pyridyl phosphoramide catalyst. The utility of the resulting bromolactones was demonstrated by transformations harnessing reactive alkyl bromide moieties without losing stereochemical information. Optimization studies and control experiments revealed that the basicity of pyridine moieties and presence of N-H protons in the phosphoramide species strongly affected both the reactivity and enantioselectivity parameters.

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 Halo-oxy- and Halo-azacyclizations Induced by Chiral Amidophosphate Catalysts and Halo-Lewis Acids

Catalytic enantioselective halocyclization of 2-alkenylphenols and enamides have been achieved through the use of chiral amidophosphate catalysts and halo-Lewis acids. Density functional theory calculations suggested that the Lewis basicity of the catalyst played an important role in the reactivity and enantioselectivity. The resulting chiral halogenated chromans can be transformed to α-Tocopherol, α-Tocotrienol, Daedalin A and Englitazone in short steps. Furthermore, a halogenated product with an unsaturated side chain may provide polycyclic adducts under radical cyclization conditions.

Highly Regio- and Enantioselective Vicinal Dihalogenation of Allyl Amides

We report a highly regio-, diastereo- and enantioselective vicinal dihalogenation of allyl amides. E- and Z-alkenes with both aryl and alkyl substituents were compatible with this chemistry. This is the result of exquisite catalyst controlled regioselectivity enabling use of electronically unbiased substrates. The reaction employs commercially available catalysts and halenium sources along with cheap inorganic halide salts to affect this transformation. A preliminary effort to extend this chemistry to heterodihalogenation is also presented.

Eosin Y-catalyzed photooxidation of triarylphosphines under visible light irradiation and aerobic conditions

A novel method for Eosin Y-catalyzed photooxidation of triarylphosphines under visible light irradiation and aerobic conditions was reported.

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.