Merging Ring-Opening 1,2-Metallate Shift with Asymmetric C(sp3)-H Borylation of Aziridines

Chiral secondary alkyl amines with a vicinal quaternary stereocenter are undoubtedly important and ubiquitous subunits in natural products and pharmaceuticals. However, their asymmetric synthesis remains a formidable challenge. Herein, we merge the ring-opening 1,2-metallate shift with iridium-catalyzed enantioselective C(sp3)-H borylation of aziridines to deliver these frameworks with high enantioselectivities. We also demonstrated the synthetic application by downstream transformations, including the total synthesis of two Amaryllidaceae alkaloids, (-)-crinane and (+)-mesmebrane.

Direct Catalytic Enantioselective Reaction of α-Isocyanoacetonitriles with Ketimines Using Cinchona Alkaloid Amide-Cu(II) Catalysts

The first enantioselective reaction of α-isocyanoacetonitriles was developed. The reaction of various α-isocyanoacetonitriles with ketimines using cinchona alkaloid amide-Cu(II) catalysts afforded imidazolines with consecutive tetrasubstituted stereogenic carbon centers in good yields and high diastereo- and enantioselectivities. The stereoselectivity of the reaction is explained on the basis of the control experiment and density functional theory (DFT) calculations. The products were subsequently converted into chiral compounds. This process highlights the possible use of α-isocyanoacetonitriles for asymmetric and organic syntheses.

Catalytic enantioselective desymmetrization of meso-aziridines

As a type of readily available small strained-ring heterocycle, meso-aziridines may undergo catalytic desymmetrizing transformations to empower the rapid construction of diverse nitrogen-containing structures bearing contiguous stereocenters, which have great relevance in natural product synthesis, drug development and the design and synthesis of chiral catalysts/ligands for asymmetric catalysis. This review outlines the advances achieved in the catalytic asymmetric desymmetrization of meso aziridines and highlights some promising avenues for further work in this realm.

An efficient catalytic method for the borohydride reaction of esters using diethylzinc as precatalyst

A cheap and easily available ZnEt2 is an effective precatalyst, which can be used for the hydroboration reaction of various organic carbonates and esters with HBpin.

Synthesis of chiral pyridine-oxazolines via catalytic asymmetric Heine reaction of meso-N-(2-picolinoyl)-aziridines

An asymmetric Heine reaction of (meso)-N-(2-picolinoyl)-aziridines catalyzed by a chiral ytterbium(III)–N,N’-dioxide complex was established. A novel library of pyridine-oxazolines was obtained in decent yields and enantioselectivities, which show potential as...

Palladium-Catalyzed, Enantioselective Desymmetrization of N-Acylaziridines with Indoles

Ring opening reactions of meso-aziridines generate chiral amine derivatives where the control of stereochemistry is possible through enantioselective catalysis. We report the use of a diphosphine-palladium(II) catalyst for the highly enantioselective desymmetrization of N-acylaziridines with indoles. The β-tryptamine products are isolated in moderate to high yield across a range of indole and aziridine substitution patterns. The synthetic utility of β-tryptamine products is demonstrated by conversion to the brominated pyrroloindoline derivative.

Cinchona Alkaloids-Derivatives and Applications

Major Cinchona alkaloids quinine, quinidine, cinchonine, and cinchonidine are available chiral natural compounds (chiral pool). Unlike many other natural products, these alkaloids are available in multiple diastereomeric forms which are separated on an industrial scale. The introduction discusses in short conformational equilibria, traditional separation scheme, biosynthesis, and de novo chemical syntheses. The second section concerns useful chemical applications of the alkaloids as chiral recognition agents and effective chiral catalysts. Besides the Sharpless ethers and quaternary ammonium salts (chiral PTC), the most successful bifunctional organocatalysts are based on 9-amino derivatives: thioureas and squaramides. The third section reports the main transformations of Cinchona alkaloids. This covers reactions of the 9-hydroxyl group with the retention or inversion of configuration. Specific Cinchona rearrangements enlarging [2.2.2]bicycle of quinuclidine to [3.2.2] products are connected to the 9-OH substitution. The syntheses of numerous esterification and etherification products are described, including many examples of bi-Cinchona alkaloid ethers. Further derivatives comprise 9-N-substituted compounds. The amino group is introduced via an azido function with the inversion of configuration at the stereogenic center C9. The 9-epi-amino-alkaloids provide imines, amides, imides, thioureas, and squaramides. The syntheses of 9-carbon-, 9-sulfur-, and 9-selenium-substituted derivatives are discussed. Oxidation of the hydroxyl group of any alkaloid gives ketones, which can be selectively reduced, reacted with Grignard reagents, or subjected to the Corey-Chaykovsky reaction. The alkaloids were also partially degraded by splitting C4'-C9 or N1-C8 bonds. In order to immobilize Cinchona alkaloids the transformations of the 3-vinyl group were often exploited. Finally, miscellaneous functionalizations of quinuclidine, quinoline, and examples of various metal complexes of the alkaloids are considered.

Enantioselective [3 + 2] Cycloaddition Reaction of Ethynylethylene Carbonates with Malononitrile Enabled by Organo/Metal Cooperative Catalysis

The first catalytic asymmetric decarboxylative [3 + 2] cycloaddition reaction of ethynylethylene carbonates with malononitrile has been developed successfully by an organo/copper cooperative system. This strategy led to a series of optically active polysubstituted dihydrofurans in good yields with high levels of enantioselectivities (up to 99% yield, 97% ee). The presence of the terminal alkynyl and the cyano group in the dihydrofuran products provides a wide scope for further structural transformations. More importantly, this organo/metal cooperative catalytic system will broaden the substrate scope and enable fundamentally new reactions.