Michael Addition Catalyzed by Chiral Secondary Amine Phosphoramide Using Fluorinated Silyl Enol Ethers: Formation of Quaternary Carbon Stereocenters

2-Oxindole and related heterocycles: synthetic methodologies for their natural products and related derivatives

Natural goods, medications, and pharmaceutically active substances all contain substituted oxindoles. Generally, the C-3 stereocenter of the substituents of oxindoles and their absolute arrangement have a substantial impact on the bioactivity of these substances. In this case, the desire for contemporary probe and drug-discovery programs for the synthesis of chiral compounds using desirable scaffolds with high structural diversity further drives research in this field. Also, the new synthetic techniques are generally simple to apply for the synthesis of other similar scaffolds. Herein, we review the distinct approaches for the synthesis of diverse useful oxindole scaffolds. Specifically, the research findings on the naturally existing 2-oxindole core and a variety of synthetic compounds having a 2-oxindole core are discussed. We present an overview of the construction of oxindole-based synthetic and natural products. In addition, the chemical reactivity of 2-oxindole and its related derivatives in the presence of chiral and achiral catalysts are thoroughly discussed. The data compiled herein provides broad information related to the bioactive product design, development, and applications of 2-oxindoles and the reported techniques will be helpful for the investigation of novel reactions in the future.

Highly Enantioselective Construction of Multifunctional Silicon-Stereogenic Silacycles by Asymmetric Enamine Catalysis

We report the first highly enantioselective construction of silicon-stereocenters by asymmetric enamine catalysis. An unprecedented desymmetric intramolecular aldolization of prochiral siladials was thus developed for the facile access of multifunctional silicon-stereogenic silacycles in high to excellent enantioselectivity. With an enal moiety, these adducts could be readily elaborated for the diverse synthesis of silicon-stereogenic compounds, and for late-stage modification.

Enantio-, Diastereo- and Regioselective Synthesis of Chiral Cyclic and Acyclic gem-Difluoromethylenes by Palladium-Catalyzed [4+2] Cycloaddition

gem-Difluoromethylene moieties are attractive in medicinal chemistry due to their ability to mimic other more ubiquitous functional groups. Thus, effective asymmetric methods for their construction are highly desirable, especially for the industrial production of chiral drugs. Using a Pd-catalyzed asymmetric [4+2] cycloaddition between substituted-2-alkylidenetrimethylene carbonates and gem-difluoroalkyl ketones, we were able to easily access chiral 1,3-dioxanes that contain a tetrasubstituted difluoroalkyl stereogenic center in cyclic and acyclic skeletons. A novel phosphoramidite ligand, which contains a bulky 1,1-dinaphthylmethanamino moiety, was developed to provide the products in high yield with excellent enantio-, diastereo-, and regioselectivity. Strikingly, the gem-difluoro substitution pattern promotes the reaction, and pentafluoroethylketone, an α,α-difluorinated β-ketoester, and a β-ketosulfone are suitable substrates for this method.

Design and Synthesis of TY-Phos and Application in Palladium-Catalyzed Enantioselective Fluoroarylation of gem-Difluoroalkenes

The first example of highly enantioselective fluoroarylation of gem-difluoroalkenes with aryl halides is presented by using a new chiral sulfinamide phosphine (Sadphos) type ligand TY-Phos. N-Me-TY-Phos can be easily synthesized on a gram scale from readily available starting materials in three steps. Salient features of this work including readily available starting materials, good yields, high enantioselectivities as well as broad substrate scope make this approach very practical and attractive. Notably, the asymmetric synthesis of an analogue of a biologically active molecule is also reported.

Catalytic Enantioselective Ynamide Additions to Isatins: Concise Access to Oxindole Alkaloids

The highly enantioselective addition of terminal ynamides to a variety of isatins, catalyzed by a bisoxazolidine copper complex under mild, base-free reaction conditions, is described. The reaction is broad in scope, scalable, applicable to unprotected isatins, and provides efficient access to 3-hydroxyoxindoles carrying a tetrasubstituted chiral center with excellent yields and enantioselectivities. Synthetically versatile, multifunctional 3-hydroxyindolinones are obtained by hydration, partial hydrogenation, or hydroxyacyloxylation of the ynamide moiety at room temperature and exhaustive hydrogenation followed by reductive detosylation and spontaneous cyclization affords cinchonamidine alkaloids.

Reinvestigation of the iodine-mediated phosphoramidation reaction of amines and P(OR)3 and its synthetic applications

A systematic study on the iodine-mediated phosphoramidation reaction of amines and trialkyl phosphites was conducted, which not only disclosed the factors affecting the reaction but also revealed that it could proceed smoothly in CH2Cl2 at room temperature in open air. Using this method, various phosphoramidates with different aliphatic amines and aromatic amines were synthesized in good to excellent yields. Our present investigation shows that this underused method is actually a mild, practical and general way to synthesize phosphoramidates and will have wide applications.

Enantioselective Mukaiyama-Michael Reaction Catalyzed by a Chiral Rhodium Complex Based on Pinene-Modified Pyridine Ligands

The rhodium complex Λ-Rh1 containing chiral pinene-modified pyridine ligands is prepared through a two-step synthetic procedure; it exhibits excellent reactivity and enantiocontrol towards the enantioselective Mukaiyama-Michael reaction of α,β-unsaturated 2-acyl imidazoles with silyl enol ethers, affording enantioenriched 1,5-dicarbonyl compounds in good yields (up to 99 %) with excellent enantioselectivities (up to 99 % ee).

Catalytic Enantioselective Michael Addition Reactions of Tertiary Enolates Generated by Detrifluoroacetylation

This work describes, for the first time, Michael addition reactions of tertiary fluoro-enolates in situ generated by detrifluoroacetylation with 1-(1-(phenylsulfonyl) vinylsulfonyl)benzene. Excellent enantioselectivity and chemical yields were achieved with application of catalysts (10 mol %) derived from Cu(OTf)₂ and (1S,2S)-1,2-diphenylethane-1,2-diamine. These reactions show a considerable degree of structural generality and allow the preparation of new types of biologically relevant molecules that contain quaternary C-F stereogenic carbon atoms and feature five-, six-, or seven-membered rings as well as heterocyclic 3-fluoro-2,3-dihydrochromen-4-one moieties.

Highly Stereoselective Gold-Catalyzed Coupling of Diazo Reagents and Fluorinated Enol Silyl Ethers to Tetrasubstituted Alkenes

We report a highly stereoselective synthesis of all-carbon or fluorinated tetrasubstituted alkenes from diazo reagents and fluorinated enol silyl ethers, using C-F bond as a synthetic handle. Cationic Au^I catalysis plays a key role in this reaction. Remarkable fluorine effects on the reactivity and selectivity was also observed.