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 1,2-diamines were synthesized from readily available O-acetyl mandelic acid. These diamines were used in the synthesis of key intermediates for the preparation of (−)-utenone A and carbovir involving enantioselective deprotonation of epoxides. The addition of Et2Zn catalysed by some of these diamines was also studied and although ees were not high, some interesting observations were made in the outcome of the stereochemistry of the product.

Synthesis of Chiral Non-racemic 1,2-Diamines from O-Acetyl Mandelic Acid: Application in Enantioselective Deprotonation of Epoxides and Diethylzinc Addition to Aldehydes.

/pdf/highly-enantioselective-direct-aldol-reaction-catalyzed-by-4aijx85qgr.pdf

Highly Enantioselective Direct Aldol Reaction Catalyzed by Organic Molecules.

Recent Advances on Stereoselective Organocatalytic Reactions. Organocatalytic Synthesis of Natural Products and Drugs

A C2-symmetric diethyl iPr-bis(oxazoline)–Cu(OAc)2·H2O was found to be an efficient catalyst for catalyzing an enantioselective Henry reaction between nitromethane and various aldehydes to provide β-hydroxy nitroalkanes with high chemical yields (up to 95%) and enantiomeric excesses (up to 97%).

Enantioselective Henry Reaction Catalyzed by a C2‐Symmetric Bis(oxazoline)—Cu(OAc)2×H2O Complex.

A variety of tert-butyldimethylsilyl (TBDMS) and tetrahydropyranyl (TFP) ethers were cleaved with ceric ammonium nitrate in methanol at 0 °C in short time. It has been shown that the reaction is chemoselective in a few cases. The primary TBDMS ethers have been cleaved selectively in the presence of THP ether and ketal.

Vinod K. Singh

Papers

Synthesis of Chiral Non-racemic 1,2-Diamines from O-Acetyl Mandelic Acid: Application in Enantioselective Deprotonation of Epoxides and Diethylzinc Addition to Aldehydes.

Highly Enantioselective Direct Aldol Reaction Catalyzed by Organic Molecules.

Recent Advances on Stereoselective Organocatalytic Reactions. Organocatalytic Synthesis of Natural Products and Drugs

Enantioselective Henry Reaction Catalyzed by a C2‐Symmetric Bis(oxazoline)—Cu(OAc)2×H2O Complex.

A Mild and Efficient Method for the Cleavage of tert- Butyldimethylsilyl and Tetrahydropyranyl Ethers by Ceric Ammonium Nitrate in Methanol.