Bimetallic Gold(I)/Chiral N , N′ ‐Dioxide Nickel(II) Asymmetric Relay Catalysis: Chemo‐ and Enantioselective Synthesis of Spiroketals and Spiroaminals

Gold(I)-Catalyzed Domino Reaction for Furopyrans Synthesis

We report herein an efficient synthesis of furopyran derivatives through a gold(I)-catalyzed domino reaction. The cascade reaction starts with two regioselective cyclizations, a 5-endo-dig and a 8-endo-dig, followed with a Grob-type fragmentation and a hetero Diels–Alder. The obtained furopyran derivatives contain fused and spiro-heterocycles. During this one-pot process, four bonds and four controlled stereogenic centers including a quaternary center are formed.

Gold-catalyzed domino reactions of alkynol and p-quinone methides: divergent synthesis of fused- and spiro-ketals

A gold-catalyzed domino reaction of alkynyl alcohols and p-quinone methides to obtain divergent fused- and spiro-ketals has been developed.

Cocatalyst-controlled divergent cascade cycloaddition reaction of arylalkynols and dioxopyrrolidienes: access to spiroketals and oxa-bridged eight-membered cyclic ethers

A cocatalyst-controlled divergent cascade cycloaddition reaction was developed for the synthesis of two different complex oxygen-containing heterocyclic compounds from arylalkynols and dioxopyrrolidienes in the presence of Au(i) catalyst.

Enantioselective Conjugate Addition of Aryl Halides and Triflates to Electron-Deficient Olefins via Nickel- and Rhodium-Catalyzed Sequential Relay Reactions

Asymmetric conjugate addition of aryl halides or aryl triflates to electron-deficient olefins was realized by sequential Miyaura borylation and Hayashi-Miyaura conjugate addition in one pot. A nickel-catalyzed borylation of aryl halides or triflates and a rhodium-chiral diene complex catalyzed enantioselective conjugate addition was executed as a pair of relay reactions as a more efficient and greener protocol.

Facile Stereoselective Approach to Diverse Spiroheterocyclic Tetrahydropyrans: Concise Synthesis of (+)-Broussonetine G and H

A highly diastereoselective copper-catalyzed multicomponent cyclization of exocyclic enol ethers/enamines with methylene malonate and aldehydes has been developed to furnish spiroheterocyclic tetrahydropyrans in high yields with greater than 95:5 d.r. This method is practical, in that 36 examples, including a range of aldehydes and exo-vinyl heterocycles, are presented. By applying the newly developed method, the total synthesis of (+)-broussonetine G and formal synthesis of (+)-broussonetine H were achieved in a concise way.

Direct Transformation of Aryl 2-Pyridyl Esters to Secondary Benzylic Alcohols by Nickel Relay Catalysis

A direct transformation of aryl esters to secondary benzylic alcohols via tandem Ni-catalyzed cross-coupling reactions of aromatic 2-pyridyl esters with alkyl zinc reagents and carbonyl group reduction by Ni-H species is achieved. Preliminary mechanistic studies reveal that the Ni-H species is generated in situ via β-hydride elimination of the Negishi reagents. The reaction is catalyzed by bench-stable nickel salts under mild conditions with wide functional group tolerance.

Synergistic silver/scandium catalytic spiroketalization of β-alkynyl ketones for the atom economical synthesis of skeletally diverse spirocyclic isochromenes

Two types of new synergistic silver/scandium catalytic spiroketalizations of β-alkynyl ketones have been achieved, delivering a variety of skeletally diverse spirocyclic isochromenes in generally good yields.

Stereoselective synthesis of 2,5-disubstituted pyrrolidines via gold-catalysed anti-Markovnikov hydroamination-initiated tandem reactions

A series of gold-catalysed intramolecular anti-Markovnikov hydroamination-initiated azidation, allylation and heteroarylation reactions of chiral homopropargyl sulfonamides have been developed. Various enantioenriched 2,5-disubstituted pyrrolidines are obtained in moderate to excellent yields with excellent enantioselectivities and generally high diastereoselectivities.

Synthesis of benzannulated spiroketals with gold-catalyzed cycloisomerization/spiroketalization cascade

An unprecedented gold-catalyzed cascade reaction of alkynyl alcohol and quinone monoimines to diverse 5,5-benzannulated spiroketals has been successfully developed.

Electrostatic self-assembled nanoparticles based on spherical polyelectrolyte brushes for magnetic resonance imaging

Electrostatic self-assemblies based on SPBs and Gd-DTPA-NO-C₄ exhibit perfect relaxometric performance.

Lewis acid catalyzed asymmetric [4+2] cycloaddition of cyclobutenones to synthesize α,β-unsaturated δ-lactones

Here we report an efficient asymmetric cycloaddition of CO double bonds with cyclobutenones catalyzed by a chiral N,N′-dioxide/Yb(iii) complex.

Asymmetric Cycloaddition and Cyclization Reactions Catalyzed by Chiral N,N'-Dioxide-Metal Complexes

Catalytic asymmetric cycloadditions and cascade cyclizations are a major focus for the enantioselective construction of chiral carbo- and heterocycles. A number of chiral Lewis acids and organocatalysts have been designed for such reactions. The development of broadly applicable catalysts bearing novel chiral backbones to meet the demands of various applications is an ongoing challenge. Approximately 10 years ago, we introduced a group of conformationally flexible C₂-symmetric N,N'-dioxide amide compounds, which represent a new class of privileged ligands. The coordination of the four oxygens of a chiral N,N'-dioxide around a central metal generates an octahedral tricyclometalated Lewis acid catalyst that can carry out various enantioselective reactions. In this Account, we summarize our recent studies on asymmetric cycloadditions between various dienophiles and dienes, dipoles and dipolarophiles, and cascade cyclizations catalyzed by chiral N,N'-dioxide-metal complexes. In principle, these unique chiral catalysts lower the LUMO energy of electron-deficient 2π components or heterodienes by coordination with the functional groups via various binding modes. With N-Boc-3-alkenyloxindole and alkylidene malonate as the electron-deficient 2π components, N,N'-dioxide-metal complexes provided excellent catalytic activities and asymmetric inductions for a variety of transformations, including [2 + 1], [3 + 2], [4 + 2], and [8 + 2] cycloadditions. Mechanistically, these substrates could be efficiently activated through bidentate coordination. The strategy was also useful for asymmetric cascade cyclizations to form polycyclic adducts. Monodentate or bidentate coordination of other α,β-unsubstituted carbonyl compounds to metal centers enabled both normal Diels-Alder reactions and inverse-electron-demand hetero-Diels-Alder reactions as well as [2 + 2] additions. Furthermore, hetero-Diels-Alder reactions of aldehydes, ketones, and imines are well-tolerated and afford various heterocycles. This includes allowing the concise synthesis of the antimalarial compound KAE609. Asymmetric Michael/cyclization reactions of bidentate α,β-unsaturated pyrazolamides gave efficient access to the chiral drugs (-)-paroxetine and (R)-thiazesim. The formal [3 + 2] cycloadditions of donor-acceptor epoxides and aziridines enantioselectively gave a series of five-membered oxo- and aza-heterocycles. The reaction of cyclopropane diketones showed unprecedented reactivities and provided a new route for the synthesis of dihydropyrrole and benzimidazole derivatives. General models for the catalytic reactions emerged from knowledge of the absolute configurations of the products of several reactions and X-ray crystal structures of the catalysts. In the field of chirality created by the coordination of an N,N'-dioxide to a metal center, the bonding of one or two reactants establishes a perfect reaction template for generation of the target adducts. Representative examples have been used to demonstrate how the substructures of the ligands and other reaction components affect the stereoselectivity and how metal salts impact the reactivity. These results reveal the importance of tunability and compatibility of the ligands and metal precursors for achieving high stereoinduction and activity.

Chiral ligands designed in China

Asymmetric catalysis has become an indispensable and productive field within the Chinese organic chemistry society. The design of chiral ligands is one of the most prominent research areas in this field. Since the late 1990s, Chinese organic chemists have developed numerous chiral ligands possessing novel chiral skeletons and design concepts. Some of these ligands have been widely adopted and can be regarded as ‘privileged ligand’, which have shown excellent performance in many asymmetric catalytic reactions. In this review, we provide an overview of the chiral ligands designed by Chinese scientists with the aim of promoting the development of this area in China and with the hope of encouraging more scientists across the world to use these ligands when designing asymmetric reactions.

Lewis acid catalyzed cascade annulation of alkynols with α-ketoesters: a facile access to γ-spiroketal-γ-lactones

A simple protocol for the synthesis of diverse unsaturated γ-spiroketal-γ-lactones has been developed by employing a Bi(OTf)₃ catalyzed cascade annulation of alkynols with α-ketoesters via a dual (π and σ) activation process.

Triple zirconocene/brønsted acid/CuO cooperative and relay catalysis system for tandem Mannich addition/C–C formative cyclization/oxidation

Triple zirconocene/brønsted acid/CuO cooperative and relay catalysis system for tandem Mannich addition/C–C formative cyclization/oxidation.

Metal-free diastereoselective construction of bridged ketal spirooxindoles via a Michael addition-inspired sequence

A TfOH-catalyzed highly diastereoselective Michael addition/ketalization sequence of 3-hydroxyoxindoles and ortho-hydroxychalcones was developed, leading to biologically important bridged ketal spirooxindoles in moderate to excellent yields.