An efficient synthesis and acylation of α-amino-β-keto-esters: Versatile intermediates in the synthesis of peptide mimetics

Highly Diastereo- and Enantioselective Access to syn-α-Amido β-Hydroxy Esters via Ruthenium-Catalyzed Dynamic Kinetic Resolution-Asymmetric Hydrogenation

Dynamic kinetic resolution (DKR) of racemic aryl α-amino β-ketoesters via Ru-diphosphine-catalyzed asymmetric hydrogenation was realized at 70 °C under 50 atm of hydrogen, affording syn α-amido β-hydroxy esters in high yields (up to 96%) with high reactivity (TON up to 940) and diastereo- and enantioselectivities (up to 99:1 dr, 98% ee). These hydrogenation products provide valuable chiral synthons in many natural products and pharmaceuticals. Gram-scale DKR asymmetric hydrogenation (DKR-AH) was also performed with retained reactivity and stereoselectivity, revealing the synthetic utility of this method.

Asymmetric transfer hydrogenation of α-amino β-keto ester hydrochlorides through dynamic kinetic resolution

The development of Ru-catalyzed asymmetric transfer hydrogenation of α-amino β-keto ester hydrochlorides is described.

Utilization of acidic α-amino acids as acyl donors: an effective stereo-controllable synthesis of aryl-keto α-amino acids and their derivatives

Aryl-keto-containing α-amino acids are of great importance in organic chemistry and biochemistry. They are valuable intermediates for the construction of hydroxyl α-amino acids, nonproteinogenic α-amino acids, as well as other biofunctional components. Friedel-Crafts acylation is an effective method to prepare aryl-keto derivatives. In this review, we summarize the preparation of aryl-keto containing α-amino acids by Friedel-Crafts acylation using acidic α-amino acids as acyl-donors and Lewis acids or Brönsted acids as catalysts.

N-Heterocyclic carbene-catalyzed direct cross-aza-benzoin reaction: Efficient synthesis of α-amino-β-keto esters

An efficient catalytic synthesis of α-amino-β-keto esters has been newly developed. Cross-coupling of various aldehydes with α-imino ester, catalyzed by N-heterocyclic carbene, leads chemoselectively to α-amino-β-keto esters in moderate to good yields with high atom efficiency. The reaction mechanism is discussed, and it is proposed that the α-amino-β-keto esters are formed under thermodynamic control.

A mild and efficient direct α-amination of β-dicarbonyl compounds using iodosobenzene and p-toluenesulfonamide catalyzed by perchlorate zinc hexahydrate

A direct α-amination of β-dicarbonyl compounds has been achieved by using iodosobenzene (PhIO) as an oxidant and p-toluenesulfonamide (TsNH(2)) as an aminating reagent in the presence of a catalytic amount of perchlorate zinc hexahydrate. The present amination reaction proceeds quickly at rt (<30 min needed for most tested substrates) to provide the corresponding α-N-tosylamido β-dicarbonyl compounds in high to excellent yields.

Rhodium carbene routes to oxazoles and thiazoles. Catalyst effects in the synthesis of oxazole and thiazole carboxylates, phosphonates, and sulfones

Dirhodium tetraacetate catalyzed reaction of alpha-diazo-beta-keto-carboxylates and -phosphonates with arenecarboxamides gives 2-aryloxazole-4-carboxylates and 4-phosphonates by carbene N-H insertion and cyclodehydration. In stark contrast, dirhodium tetrakis(heptafluorobutyramide) catalysis results in a dramatic change of regioselectivity to give oxazole-5-carboxylates and 5-phosphonates. Alpha-diazo-beta-ketosulfones behave similarly and give 5-sulfonyloxazoles upon dirhodium tetrakis(heptafluorobutyramide) catalyzed reaction with carboxamides. The analogous reactions of thiocarboxamides give the corresponding thiazole-5-carboxylates, -phosphonates, and -sulfones.

Molecular scaffold for the construction of three-armed and cage-like receptors

An efficient procedure was developed for the synthesis of the C3-symmetric molecular scaffold 2. The latter can easily be converted by a single step into either the three-armed receptors 11-16 or the cage-like receptor 17. X-ray structures were obtained for 2, 11, and 16, which are discussed in regard to their aptitude as receptor platforms. The interaction of the three-armed receptors 12-16 and the cage-like receptor 17 with phloroglucinol was investigated. In accordance with the conclusions obtained from molecular modeling and X-ray crystallographic studies on the host-guest complexes, the three-armed bipyridine receptor 16 exhibits, due to its induced fit, a larger association constant toward phloroglucinol than the cage 17. This new receptor system shows all of the positive features characteristic of 2,4,6-trialkylbenzene receptor systems, such as conformational control by steric gearing, ready availability, and versatility in derivatization. These attributes, combined with the advantageous size of the components, allows this system to be readily tailored to provide receptors for larger, biologically important molecules.

A practical approach to the synthesis of 2,4-disubstituted oxazoles from amino acids

[reaction: see text] A new sequence for the synthesis of various 2,4-disubstituted oxazoles from alpha-amino acids is reported. The method is shown to be general and incorporates the reagent combination, triphenylphosphine/hexachloroethane, for cyclodehydration of intermediate alpha-acylamino aldehydes. Implementation of this reagent system for the conversion of alpha-acylamino ketones to oxazoles is briefly investigated.