About Dendrimers: Structure, Physical Properties, and Applications

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

Large-scale applications of transition metal-catalyzed couplings for the synthesis of pharmaceuticals.

Enantioselective addition of organozinc reagents to aldehydes

THE homochirality of natural amino acids and sugars remains a puzzle for theories of the chemical origin of life1–18. In 1953 Frank7 proposed a reaction scheme by which a combination of autocatalysis and inhibition in a system of replicating chiral molecules can allow small random fluctuations in an initially racemic mixture to tip the balance to yield almost exclusively one enantiomer. Here we show experimentally that autocatalysis in a chemical reaction can indeed enhance a small initial enantiomeric excess of a chiral molecule. When a 5-pyrimidyl alkanol with a small (2%) enantiomeric excess is treated with diisopropylzinc and pyrimidine-5-car-boxaldehyde, it undergoes an autocatalytic reaction to generate more of the alkanol. Because the reaction involves a chiral catalyst generated from the initial alkanol, and because the catalytic step is enantioselective, the enantiomeric excess of the product is enhanced. This process provides a mechanism by which a small initial imbalance in chirality can become overwhelming.

Asymmetric autocatalysis and amplification of enantiomeric excess of a chiral molecule

Catalytic asymmetric induction. Highly enantioselective addition of dialkylzincs to aldehydes using chiral pyrrolidinylmethanols and their metal salts

Asymmetric autocatalysis is a process of automultiplication of a chiral compound in which chiral product acts as a chiral catalyst for its own production. The discovery and the development of asymmetric autocatalysis of pyrimidyl-, quinolyl-, and pyridylalkanols are described in the enantioselective additions of diisopropylzinc to the corresponding nitrogen-containing aldehydes. (Alkynylpyrimidyl)alkanols automultiply with a yield of over 99% and over 99.5% ee. Asymmetric autocatalysts with extremely low ee's automultiply with significant amplification of ee's without the need for any other chiral auxiliaries. Small enantiomeric imbalances of chiral molecules induced by physical factors can be amplified by the present asymmetric autocatalysis.

Kenso Soai

Papers

Enantioselective addition of organozinc reagents to aldehydes

Asymmetric autocatalysis and amplification of enantiomeric excess of a chiral molecule

Catalytic asymmetric induction. Highly enantioselective addition of dialkylzincs to aldehydes using chiral pyrrolidinylmethanols and their metal salts

Enantioselective Automultiplication of Chiral Molecules by Asymmetric Autocatalysis

d- and l-Quartz-Promoted Highly Enantioselective Synthesis of a Chiral Organic Compound