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

Ring opening of activated cyclic amines to produce amino carbonyl compounds has been studied in the presence of Lewis acids. Whereas five- and six-membered rings cleave and rearrange via a 1,2-hydride shift, reaction in three- and four-membered rings takes place via a C−C bond migration. In the case of a three-membered ring, a wide variety of Lewis acids proved to be effective for the reaction. Base-induced ring opening of activated α,α-disubstituted azetidinemethanol and its mechanistic aspects have been studied.

Lewis Acid‐Mediated Rearrangement of Activated Cyclic Amines: A Facile Synthetic Protocol for the Preparation of Amino Carbonyl Compounds.

In the presence of a catalytic amount of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), tetrahydropyranyl ethers are readily hydrolysed to their corresponding alcohols in wet acetonitrile under mild conditions.

DDQ as a Mild and Efficient Catalyst for Deprotection of Tetrahydropyranyl Ethers.

Starting from various methyl 2-formyl benzoates, hydroxyacetone and aryl amines the scalable title reaction is elaborated providing the products in high yields, with high dia- and enantioselectivity.

An Efficient Entry to syn- and anti-Selective Isoindolinones via an Organocatalytic Direct Mannich/Lactamization Sequence.

Efficient Method for Cleavage of Aziridines with Aromatic Amines.

An efficient ring cleavage of aziridines with acids has been studied in the absence of any catalyst. The hydrolysis of the products, amino esters, leads to the corresponding amino alcohols. The reaction has been extended to chiral cycloalkyl aziridines, leading to the formation of diastereomers. After separation, these diastereomers have been converted to optically pure amino alcohols in two steps.

Vinod K. Singh

Papers

Lewis Acid‐Mediated Rearrangement of Activated Cyclic Amines: A Facile Synthetic Protocol for the Preparation of Amino Carbonyl Compounds.

DDQ as a Mild and Efficient Catalyst for Deprotection of Tetrahydropyranyl Ethers.

An Efficient Entry to syn- and anti-Selective Isoindolinones via an Organocatalytic Direct Mannich/Lactamization Sequence.

Efficient Method for Cleavage of Aziridines with Aromatic Amines.

Efficient Ring Opening of Aziridines with Carboxylic Acids.