Asymmetric enamine catalysis.

Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aube rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.

Organic Azides: An Exploding Diversity of a Unique Class of Compounds

Hydrogenation is a core technology in chemical synthesis. High rates and selectivities are attainable only by the coordination of structurally well-designed catalysts and suitable reaction conditions. The newly devised [RuCl(2)(phosphane)(2)(1,2-diamine)] complexes are excellent precatalysts for homogeneous hydrogenation of simple ketones which lack any functionality capable of interacting with the metal center. This catalyst system allows for the preferential reduction of a C=O function over a coexisting C=C linkage in a 2-propanol solution containing an alkaline base. The hydrogenation tolerates many substituents including F, Cl, Br, I, CF(3), OCH(3), OCH(2)C(6)H(5), COOCH(CH(3))(2), NO(2), NH(2), and NRCOR as well as various electron-rich and -deficient heterocycles. Furthermore, stereoselectivity is easily controlled by the electronic and steric properties (bulkiness and chirality) of the ligands as well as the reaction conditions. Diastereoselectivities observed in the catalytic hydrogenation of cyclic and acyclic ketones with the standard triphenylphosphane/ethylenediamine combination compare well with the best conventional hydride reductions. The use of appropriate chiral diphosphanes, particularly BINAP compounds, and chiral diamines results in rapid and productive asymmetric hydrogenation of a range of aromatic and heteroaromatic ketones and gives a consistently high enantioselectivity. Certain amino and alkoxy ketones can be used as substrates. Cyclic and acyclic alpha,beta-unsaturated ketones can be converted into chiral allyl alcohols of high enantiomeric purity. Hydrogenation of configurationally labile ketones allows for the dynamic kinetic discrimination of diastereomers, epimers, and enantiomers. This new method shows promise in the practical synthesis of a wide variety of chiral alcohols from achiral and chiral ketone substrates. Its versatility is manifested by the asymmetric synthesis of some biologically significant chiral compounds. The high rate and carbonyl selectivity are based on nonclassical metal-ligand bifunctional catalysis involving an 18-electron amino ruthenium hydride complex and a 16-electron amido ruthenium species.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/1521-3773%2820010105%2940%3A1%3C40%3A%3AAID-ANIE40%3E3.0.CO%3B2-5

Asymmetric Catalysis by Architectural and Functional Molecular Engineering: Practical Chemo‐ and Stereoselective Hydrogenation of Ketones

Recent Advances in the Baylis−Hillman Reaction and Applications

1,2-Amino Alcohols and Their Heterocyclic Derivatives as Chiral Auxiliaries in Asymmetric Synthesis

Epoxides on treatment with DMSO, oxalyl chloride, and 10 mole % of methanol in the presence of triethylamine at −60° C are converted to α-chloro ketones in high yield.

A Mild Method for Conversion of Epoxides into α‐Chloro Ketones.

The catalytic enantioselective Friedel-Crafts reaction of indoles with 2-enoylpyridine 1-oxides has been studied in the presence of chiral pyridine 2,6-bis(5',5'-diphenyloxazoline)-Cu(II) complexes. The reaction furnished alkylated indoles in excellent yields (up to 97%) and enantioselectivities (up to 99% ee).

Highly Enantioselective Friedel—Crafts Reaction of Indoles with 2-EnoylPyridine 1-Oxides Catalyzed by Chiral Pyridine 2,6-Bis(5′,5′-diphenyloxazoline)—Cu(II) Complexes.

The reaction is general for various N-oxides tolerating aromatic, aliphatic and alkenic substituents and affords the products with enantioselectivities up to 96% e.e.

Enantioselective Michael Addition of Malonates to 2‐Enoylpyridine N‐Oxides Catalyzed by Chiral Bisoxazoline—Zn(II) Complex.

Excellent selectivity for terminal attack of the diene component is observed except for reactions involving o-substituted aniline components like (IX).

Ni(II)-Catalyzed Highly Stereo- and Regioselective Syntheses of Isoindolinones and Isoquinolinones from in situ Prepared Aldimines Triggered by Homoallylation/Lactamization Cascade.

The reactions of alkyl nitriles, acetyl chloride, aldehydes and β-ketoesters or simple ketones was studied for the one-pot synthesis of β-acetamido carbonyl compounds. It was observed that the reaction proceeds in the absence of Lewis acids. However, a Lewis acid catalyzes the reaction and several were tested. It was found that whereas Cu(OTf) 2 is suitable for the coupling of β-ketoesters with aldehydes, Sc(OTf) 3 is the best for ketones. A possible mechanism is proposed based on the isolation and characterization of an intermediate.

Vinod K. Singh

Papers

A Mild Method for Conversion of Epoxides into α‐Chloro Ketones.

Highly Enantioselective Friedel—Crafts Reaction of Indoles with 2-EnoylPyridine 1-Oxides Catalyzed by Chiral Pyridine 2,6-Bis(5′,5′-diphenyloxazoline)—Cu(II) Complexes.

Enantioselective Michael Addition of Malonates to 2‐Enoylpyridine N‐Oxides Catalyzed by Chiral Bisoxazoline—Zn(II) Complex.

Ni(II)-Catalyzed Highly Stereo- and Regioselective Syntheses of Isoindolinones and Isoquinolinones from in situ Prepared Aldimines Triggered by Homoallylation/Lactamization Cascade.

Synthesis of Mannich Type Products via a Three-Component Coupling Reaction.