N,N′-Dioxide/Gadolinium(III)-Catalyzed Asymmetric Conjugate Addition of Nitroalkanes to α,β-Unsaturated Pyrazolamides

Stereoselective Synthesis of Chiral Hydrophenanthridines via a One-Pot Stepwise Aza-Michael/Michael/Michael Process

A one-pot, two-step aza-Michael/Michael/Michael process was developed to diastereospecifically construct C6a,C10a-cis-hydrophenanthridines in a highly enantioselective manner (83-99% ee). The tricyclic products were provided in 50-99% isolated yields, sequentially promoted by bifunctional squaramide and diamine in a one-pot operation. This doubly annulative protocol indicated that the complicated polycyclic structures could be easily constructed via full employment of the available reaction sites of readily prepared precursors.

Asymmetric Catalytic Rearrangements with α-Diazocarbonyl Compounds

α-Diazocarbonyl compounds serve as nucleophiles, dipoles, carbene precursors, and rare electrophiles, enabling a vast array of organic transformations under the influence of metal catalysts. Among them, rearrangement processes are attractive and provide straightforward and efficient accesses to one-carbon extension adducts or heteroatom-containing molecules. The reactions occur upon the release of dinitrogen after nucleophilic addition or before ylide formation. Although significant progress has been made for these two types of rearrangement reactions, the issue of enantiocontrol is challenging because the final optically enriched products are generated via multistep transformations and the inherent spacial arrangement of the intermediates has more or less influence on the regio- and enantioselectivity.In this Account, we collected several rearrangements of α-diazocarbonyl compounds, showcasing the efficient catalysts and tailored strategies for tackling enantioselective varieties of these two types of rearrangement reactions. Our research group initiated the catalytic asymmetric reactions of α-diazocarbonyl compounds during the development of chiral Feng N,N'-dioxide-metal complex catalysts and others. As a kind of useful chiral Lewis acid catalyst chiral N,N'-dioxide-metal complexes are favorable for the activation of various carbonyl compounds, accelerating the diastereo- and enantioselective nucleophilic addition of α-diazoesters and the sequential rearrangements in either an intermolecular or intramolecular manner. Aldehydes, acyclic and cyclic ketone derivatives, and α,β-unsaturated ketones could participate in efficient asymmetric homologation reactions, and an obvious ligand-acceleration effect is observed in these processes. For example, the Roskamp-Feng reaction of aldehydes gives optically active β-ketoesters through a H-shift, overwhelming the aryl group shift or oxygen attack. The shift preference and enantiocontrol in the homologation of acyclic and cyclic ketone derivatives could be under excellent control of the chiral catalysts. An unusual electrophilic α-amination of aryl/alkyl ketones and even a complicated homologation/dyotropic rearrangement/interconversion/[3 + 2] cycloaddition cascade used to construct dimeric polycyclic compounds were discovered as a result of the selection of chiral ligands and additives. On the basis of the understanding of the interaction of the functional group with N,N'-dioxide-metal complexes in catalysis and the key enantio-determining issues in ylide-based rearrangements, we designed new α-diazocarbonyl compounds by introducing a pyrazole-1-carboxyl group as the acceptor unit, which could benefit the formation of both carbenoid species and the chiral catalyst-bound ylides to deliver stereoselectivity. Taking advantage of Ni(II) or Co(II) complexes of Feng N,N'-dioxide ligands, we realized several kinds of enantioselective [2,3]-sigmatropic rearrangements, such as the Doyle-Kirmse reaction with allylic sulfides or selenides, [2,3]-Stevens rearrangements of vinyl-substituted α-diazo pyrazoleamides with thioacetates, Sommelet-Hauser rearrangements of aryl-substituted α-diazo pyrazoleamides with thioamides, and thio-Claisen rearrangements of 2-thio-indoles as well. Moreover, this strategy was shown to be applicable to highly γ-selective and enantioselective insertion into N-H bonds of secondary amines with vinyl-substituted α-diazo pyrazoleamides.

Synthesis of chiral β-substituted γ-amino-butyric acid derivatives via enantioconvergent ring opening of racemic 2-(hetero)aryl aziridines with ketene silyl acetals

Lewis acid-catalyzed enantioconvergent ring opening of racemic 2-(hetero)aryl-N-sulfonyl aziridines with ketene silyl acetals is developed.

Catalysts’ evolution in the asymmetric conjugate addition of nitroalkanes to electron-poor alkenes

This review provides a journey of the catalyst usage for the enantioselective conjugate addition of nitroalkanes to electron-poor olefins from the early attempts to the latest achievements. Selected applications are also reported.

Asymmetric Catalytic Synthesis of Hexahydropyrrolo-isoquinolines via Three-Component 1,3-Dipolar-Cycloaddition

An asymmetric three-component 1,3-dipolar cycloaddition of 3,4-dihydroisoquinolines, bromoacetates and α,β-unsaturated pyrazole amide is realized by using a chiral N,N'-dioxide-Y(OTf)₃ complex as the catalyst. The process includes a base-promoted formation of dihydroisoquinolium ylides in situ, and a chiral Lewis acid-catalyzed asymmetric [3+2] cycloaddition with α,β-unsaturated pyrazole amides. A series of hexahydropyrrolo-isoquinolines are obtained in moderate to good yields with excellent diastereo- and enantioselectivities.

Chiral N,N'-dioxide/Mg(OTf)2 complex-catalyzed asymmetric [2,3]-rearrangement of in situ generated ammonium salts

Catalytic enantioselective [2,3]-rearrangements of in situ generated ammonium ylides from glycine pyrazoleamides and allyl bromides were achieved by employing a chiral N,N'-dioxide/MgII complex as the catalyst. This protocol provided a facile and efficient synthesis route to a series of anti-α-amino acid derivatives in good yields with high stereoselectivities. Moreover, a possible catalytic cycle was proposed to illustrate the reaction process and the origin of stereoselectivity.

Highly enantioselective Michael addition of α-nitroacetate to α,β-unsaturated pyrazolamide catalyzed by a bifunctional squaramide

A highly enantioselective (91- > 99% ee) Michael addition of α-nitroacetate to α,β-unsaturated pyrazolamide was developed in the presence of a bifunctional squaramide. Satisfactory isolated yields (42%-99%) have been achieved with a wide range of α,β-unsaturated pyrazolamides, albeit acceptor of this type displayed poor reactivity in the precedent reports. The adducts resulting from this protocol are useful synthetic intermediates for further synthetic modification.

Recent Advances in Metal-Catalyzed Asymmetric 1,4-Conjugate Addition (ACA) of Nonorganometallic Nucleophiles

The metal-catalyzed asymmetric conjugate addition (ACA) reaction has emerged as a general and powerful approach for the construction of optically active compounds and is among the most significant and useful reactions in synthetic organic chemistry. In recent years, great progress has been made in this area with the use of various chiral metal complexes based on different chiral ligands. This review provides comprehensive and critical information on the enantioselective 1,4-conjugate addition of nonorganometallic (soft) nucleophiles and their importance in synthetic applications. The literature is covered from the last 10 years, and a number of examples from before 2007 are included as background information. The review is divided into multiple parts according to the type of nucleophile involved in the reaction (such as C-, B-, O-, N-, S-, P-, and Si-centered nucleophiles) and metal catalyst systems used.

Enantioselective Synthesis of N-H-Free 1,5-Benzothiazepines

An enantioselective sulfa-Michael-cyclization reaction was developed for the synthesis of 1,5-benzothiazepines with versatile pharmacological activities. The reaction between 2-aminothiophenol and α,β-unsaturated pyrazoleamides gave direct access to N-H-free 1,5-benzothiazepines in the presence of a chiral N,N'-dioxide/Yb(OTf)₃ complex. Excellent enantioselectivities (up to 96 % ee) and high yields (up to 99 %) were obtained for a broad range of substrates under mild reaction conditions. This method provided a facile approach to the antidepressant drug (R)-(-)-Thiazesim.

Catalytic Michael/Ring-Closure Reaction of α,β-Unsaturated Pyrazoleamides with Amidomalonates: Asymmetric Synthesis of (-)-Paroxetine

A highly enantioselective tandem Michael/ring-closure reaction of α,β-unsaturated pyrazoleamides and amidomalonates has been accomplished in the presence of a chiral N,N'-dioxide-Yb(OTf)₃ complex (Tf: trifluoromethanesulfonyl) to give various substituted chiral glutarimides with high yields and diastereo- and enantioselectivities. Moreover, this methodology could be used for gram-scale manipulation and was successfully applied to the synthesis of (-)-paroxetine. Further nonlinear and HRMS studies revealed that the real catalytically active species was a monomeric L-PMe₂ -Yb³⁺ complex. A plausible transition state was proposed to explain the origin of the asymmetric induction.

Synthesis of Chiral Tetrahydrofurans via Catalytic Asymmetric [3 + 2] Cycloaddition of Heterosubstituted Alkenes with Oxiranes

An efficient diastereo- and enantioselective [3 + 2] cycloaddition of heterosubstituted alkenes with oxiranes via selective C-C bond cleavage of epoxides has been developed. The reaction was catalyzed by a chiral N,N'-dioxide/Ni(II) catalyst, and a variety of chiral highly substituted tetrahydrofurans were obtained in up to 99% yield, 92/8 dr, and 99% ee.

Asymmetric synthesis of functionalized pyrrolizidines by an organocatalytic and pot-economy strategy

An enantioselective synthesis of indolizidines was achieved with a one-step purification by sequential asymmetric Michael–oxidative esterification–Michael–reduction–reductive Mannich–amidation reactions.

Efficient Synthesis of Chiral Trisubstituted 1,2-Allenyl Ketones by Catalytic Asymmetric Conjugate Addition of Malonic Esters to Enynes

An N,N'-dioxide/scandium(III) complex catalyzed, highly efficient conjugate addition of malonic esters to enynes is described. A range of trisubstituted 1,2-allenyl ketones were obtained in high yields (up to 99 %) with good d.r. (up to 95/5) and excellent ee values (97 %-99 %). Moreover, the products could be easily transformed into chiral furan and 5-hydroxypyrazoline derivatives, both of which are important skeletons of many biologically active compounds and pharmacologicals.

Gadolinium-Catalyzed Regio- and Enantioselective Aminolysis of Aromatic trans-2,3-Epoxy Sulfonamides

The first enantioselective aminolysis of aromatic trans-2,3-epoxy sulfonamides has been accomplished, which was efficiently catalyzed by a Gd-N,N'-dioxide complex. Under the directing effect of the sulfonamide moiety the ring-opening reaction proceeded selectively at the C-3 position in a highly enantioselective manner furnishing various Ts- and SES-protected 3-amino-3-phenylpropan-2-olamines as products.