H-Bond Donor-Directed Switch of Diastereoselectivity in the Enantioselective Intramolecular Aza-Henry Reaction of Ketimines

We report an H-bond donor controlled diastereoselective switchable intramolecular aza-Henry reaction of ketimines derived from α-ketoesters and 2-(2-nitroethyl)anilines, allowing facile access to chiral tetrahydroquinolines bearing an aza-quaternary carbon stereocenter, which are privileged scaffold for medicinal researches. While newly developed cinchona alkaloid derived phosphoramide-bearing quaternary ammonium salt C2 selectively give cis-adducts in up to 20 : 1 dr and 99 % ee, the corresponding urea-bearing analogue C8 preferentially give trans-adducts in up to 20 : 1 dr and 99 % ee.

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.

Au-Catalyzed Formal Allylation of Diazo(thio)oxindoles: Application to Tandem Asymmetric Synthesis of Quaternary Stereocenters

We report an efficient Au(I)-catalyzed formal allylation of diazo(thio)oxindoles using allyltrimethylsilane to give 3-allyl (thio)oxindoles, which are difficult to access by using traditional alkylation methods under basic conditions. The approach enables a highly stereoselective synthesis of quaternary (thio)oxindoles via a formal allylation-asymmetric Michael addition sequence. These adducts are versatile synthons for spirocyclic (thio)oxindoles. Initial biological studies reveal that chiral thiooxindoles show promising antiproliferation activity that is better than that of the corresponding oxindoles.

H-bond donor-directed switching of diastereoselectivity in the Michael addition of α-azido ketones to nitroolefins

The development of catalyst-controlled stereodivergent asymmetric catalysis is important for providing facile access to all stereoisomers of chiral products with multiple stereocenters from the same starting materials. Despite progress, new design strategies for diastereodivergent asymmetric catalysis are still highly desirable. Here we report the potency of H-bond donors as the governing factor to tune diastereoselectivity in a highly diastereoselective switchable enantioselective Michael addition of α-azido ketones to nitroolefins. While a newly developed bifunctional tertiary amine, phosphoramide, preferentially afforded syn-adducts, an analogous squaramide catalyst selectively gave anti-adducts. The resulting multifunctional tertiary azides can be converted to spiro-pyrrolidines with four continuous stereocenters in a one-pot operation. Mechanistic studies cast light on the control of diastereoselectivity by H-bond donors. While the squaramide-catalyzed reaction proceeded with a transition state with both squaramide N–H bonds binding to an enolate intermediate, an unprecedented model was proposed for the phosphoramide-mediated reaction wherein an amide N–H bond and an alkylammonium ion formed in situ interact with nitroolefins, with the enolate stabilized by nonclassical C–H⋯O hydrogen-bonding interactions.

We report the successful reversal of the diastereoselectivity in an unprecedented Michael addition of α-azido ketones to nitroolefins catalyzed by bifunctional tertiary amines, simply by varying the H-bond donor from phosphoramide to squaramide.

Development of Synthetic Methodologies via Catalytic Enantioselective Synthesis of 3,3-Disubstituted Oxindoles

3,3-Disubstituted oxindoles are widely distributed in natural products, drugs, and pharmaceutically active compounds. The absolute configuration and the substituents on the fully substituted C3 stereocenter of the oxindole often significantly influence the biological activity. Therefore, tremendous efforts have made to develop catalytic enantioselective syntheses of this prominent structural motif. Research in this area is further fueled by the ever-increasing demand for modern probe- and drug-discovery programs for synthetic libraries of chiral compounds that are derived from privileged scaffolds with high structural diversity. Notably, the efficient construction of fully substituted C3 stereocenters of oxindole, tetrasubstituted or all-carbon quaternary, spirocyclic or not, also becomes a test ground for new synthetic methodologies. We have been engaged in developing efficient methods for diversity-oriented synthesis of chiral 3,3-disubstituted oxindoles from readily available starting materials. We have systematically developed catalytic enantioselective methods to prepare 3-substituted 3-hydroxyoxindoles, 3-aminooxindoles, and 3-thiooxindoles, quaternary oxindoles, and spirocyclic oxindoles. These protocols can be classified into six approaches: (1) enantioselective addition of nucleophiles to isatins or isatin ketimines; (2) unprotected 3-substituted oxindoles as nucleophiles; (3) functionalization of oxindole-derived tetrasubstituted alkenes; (4) desymmetrization of oxindole-based diynes; (5) spirocyclopropyl oxindoles as donor-acceptor (D-A) cyclopropanes; and (6) elaboration of diazooxindoles. By the use of these methods, chiral oxindoles with rich structural diversity are readily accessed with high to excellent enantioselectivity. Some methods have been used for the enantioselective formal or total synthesis of natural products, bioactive compounds, or their analogues. On the basis of these studies, we developed synthetic methodologies that have potential application. We designed phosphoramide-based bifunctional catalysts for the efficient construction of quaternary oxindoles: a cinchona-alkaloid-derived phosphoramide for the Michael addition of unprotected 3-substituted oxindoles to nitroolefins with broad substrate scope and a chiral 1,2-cyclohexanediamine-derived bifunctional phosphoramide for the activation of fluorinated enol silyl ethers for the addition to isatylidene malononitrile. The phosphoramide-based catalysts achieved better enantiofacial control than the analogous H-bond-donor-derived catalysts in these reactions, suggesting the potential of the former in new chiral catalyst development. We identified chiral Au(I) and Hg(II) catalysts for olefin cyclopropanation of diazooxindoles. We further disclosed the effective activation of spirocyclopropyl oxindoles by using electron-withdrawing N-protecting groups for enantioselective [3 + 3] cycloaddition, offering the promise of constructing a diverse range of spirocyclic oxindoles by the use of such monoactivated D-A cyclopropanes. We developed tandem sequences that allow the facile synthesis of 3,3-disubstituted oxindoles from simple starting materials in a one-pot operation, including a tandem Morita-Baylis-Hillman/bromination/[3 + 2] annulation sequence, a hydrogenation/ketimine formation/asymmetric 6π electrocyclization sequence, a C-H functionalization/Michael addition or amination sequence, and an aza-Wittig/Strecker sequence. We designed oxindole-based diynes to realize a highly enantioselective Cu-catalyzed alkyne-azide cycloaddition (CuAAC), outlining the desymmetrization of prochiral diynes as an effective strategy to exploit asymmetric CuAAC. This Account focuses on the synthetic methodologies developed in our group for the catalytic enantioselective synthesis of 3,3-disubstituted oxindoles and provides an overview of our research on the design, development, and applications of these methods that will provide useful insights for the exploration of new reactions.

Catalytic asymmetric synthesis of hetero-substituted oxindoles

The construction of chiral disubstituted oxindoles is an intriguing challenge for organic chemists.

Rhodium(ii)-catalyzed direct sulfenylation of diazooxindoles with disulfides

Rhodium(ii)-catalyzed reactions for direct sulfenylation of diazooxindoles with disulfides via C–S bond formation was developed.

The first catalytic asymmetric thioacetalization by chiral phosphoric acid catalysis

We report here the first catalytic asymmetric thioacetalization of salicylaldehyde and dithiol. Chiral phosphoric acid STRIP C5 is identified as a powerful catalyst for this reaction to afford various chiral dithioacetals in high to excellent yields and enantioselectivities under mild conditions.

Sequential Au(i)/chiral tertiary amine catalysis: a tandem C–H functionalization of anisoles or a thiophene/asymmetric Michael addition sequence to quaternary oxindoles

We report an unprecedented sequential Au(i)/bifunctional tertiary amine catalysis, which enables a tandem C–H functionalization of weak nucleophiles (anisoles or thiophenes) and asymmetric Michael addition for the highly enantioselective synthesis of quaternary oxindoles.

Organocatalytic enantioselective Mukaiyama–Mannich reaction of fluorinated enol silyl ethers and cyclic N-sulfonyl ketimines

The first catalytic asymmetric Mukaiyama–Mannich reaction of fluorinated silyl enol ethers and ketimines is developed, allowing highly enantioselective synthesis of benzosultam based β-fluorinated C^α-tetrasubstituted α-amino acid derivatives.

Chemo- and Enantioselective Addition and β-Hydrogen Transfer Reduction of Carbonyl Compounds with Diethylzinc Reagent in One Pot Catalyzed by a Single Chiral Organometallic Catalyst

Using a single chiral phosphoramide-Zn(II) complex as the catalyst, the asymmetric β-H transfer reduction of aromatic α-trifluoromethyl ketones and enantioselective addition of aromatic aldehydes with Et2Zn in one pot were successfully realized, affording the corresponding additive products of secondary alcohols in high yields (up to 99%) with excellent enantioselectivities (up to 98% ee) and the reduction products of α-trifluoromethyl alcohols in good to excellent yields with up to 77% ee.

Catalytic asymmetric sulfenylation to structurally diverse dithioketals

We report the first example of highly enantioselective synthesis of structurally diverse chiral dithioketals via asymmetric sulfenylation of various types of S-based nucleophiles, catalyzed by a cheap cinchona alkaloid derivative, dihydroquinine.

Catalytic asymmetric synthesis of polysubstituted spirocyclopropyl oxindoles: organocatalysis versus transition metal catalysis

Recent progress in catalytic asymmetric synthesis of spirocyclopropyl oxindoles via organocatalysis and transition metal catalysis are summarized and discussed.

Expedient synthesis of tetrasubstituted pyrroles via a copper-catalyzed cascade inter-/intramolecular cyclization of 1,3-enynes carry a nitro group with amines

Various tetrasubstituted pyrroles/pyrazoles have been prepared from nitro-substituted 1,3-enynes with aromatic amines/hydrazinesviaa copper-catalyzed cascade aza-Michael addition, cyclization and aromatization.