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

A variety of activated aziridines were cleaved by sodium azide and sodium cyanide in aqueous acetonitrile at reflux, in the absence of any Lewis acid, to provide ring-opened products in quantitative yields. However, the reaction was sluggish in the ring opening of unactivated aziridines with sodium azide where the yields could be increased by adding 50 mol% CuCl2·2H2O. The reaction was used to synthesize chiral diamines.

Do Aziridines Require Lewis Acids for Cleavage with Ionic Nucleophiles

Chemistry is a broad discipline that overlaps extensively with Biology, Medicine, Materials science, Physics, and many other areas. There has often been a view expressed and shared among Indian chemists that the discipline has not been properly represented, and its vitality and vigor were not adequately recognized in India. 

The Chemical Research Society of India (CRSI)

The reaction of epoxides with chiral nonracemic lithium amide bases, designed and prepared from (R)-phenylglycine, has been studied in detail. A maximum of 80% ee was obtained for conversion of cyclohexene oxide to (S)-2-cyclohexen-1-ol. Enantioselective deprotonation of a variety of other epoxides was studied. A cyclopentanoid core unit for prostaglandin synthesis was synthesized in 97% ee.

Design, Synthesis, and Application of Chiral Nonracemic Lithium Amide Bases in Enantioselective Deprotonation of Epoxides.

A variety of N-substituted aziridines have been opened with TMS azide in MeCN at rt in the absence of any Lewis acid. The reaction was extended to the synthesis of (R,R)- and (S,S)-1,2-diaminocyclohexane.

An Efficient Method for Opening Nonactivated Aziridines with TMS Azide: Application in the Synthesis of Chiral 1,2-Diaminocyclohexane.

The reactions can also be performed using Zn(OTf)2 or Cu(OTf)2 for the synthesis of isoindoles or isoquinolines, respectively.

Vinod K. Singh

Papers

Do Aziridines Require Lewis Acids for Cleavage with Ionic Nucleophiles

The Chemical Research Society of India (CRSI)

Design, Synthesis, and Application of Chiral Nonracemic Lithium Amide Bases in Enantioselective Deprotonation of Epoxides.

An Efficient Method for Opening Nonactivated Aziridines with TMS Azide: Application in the Synthesis of Chiral 1,2-Diaminocyclohexane.

A General Catalytic Route to Isoindolinones and Tetrahydroisoquinolines: Application in the Synthesis of (.+‐.)‐Crispine A.