Catalytic asymmetric Pictet-Spengler reaction

A catalytic asymmetric Pictet-Spengler reaction has been developed, wherein treating substituted tryptamines with an aldehyde in the presence of a catalytic amount of a chiral phosphoric acid provides the corresponding tetrahydro-beta-carboline derivatives in high yields and enantiomeric excesses. The reaction works well with both aliphatic and aromatic aldehydes.     

Catalytic asymmetric Henry reaction

The classical Henry reaction, the coupling of a nitroalkane with a carbonyl compound in the presence of a base, is an important C–C bond forming reaction in organic chemistry giving β-nitroalcohols, which are useful synthons in organic synthesis. However, an asymmetric version of the reaction, that has been developed recently, gives a new dimension to the classical Henry reaction whereby the control of stereochemistry of two newly generated carbon centres has become possible. In this review, the various catalytic methods for this purpose are discussed.     

催化不对称Friedel-Crafts反应

傅-克反应是有机化学中最基本的反应之一,但是对于催化的不对称傅-克反应的研究则处于起步阶段。最近这方面的研究获得了突破,本文简要介绍了催化不对称傅-克反应的最新动态,包括各种手性Lewis酸催化体系的开发及其在不对称合成中的应用。     

Scope of the asymmetric intramolecular stetter reaction catalyzed by chiral nucleophilic triazolinylidene carbenes

A highly enantioselective intramolecular Stetter reaction of aromatic and aliphatic aldehydes tethered to different Michael acceptors has been developed. Two triazolium scaffolds have been identified that catalyze the intramolecular Stetter reaction with good reactivity and enantioselectivity. The substrate scope has been examined and found to be broad; both electron-rich and -poor aromatic aldehydes undergo cyclization in high yield and enantioselectivity. The tether can include oxygen, sulfur, nitrogen, and carbon linkers with no detrimental effects. In addition, the incorporation of various tethered Michael acceptors includes amides, esters, thioesters, ketones, aldehydes, and nitriles. The catalyst loading may be reduced to 3 mol % without significantly affecting the reactivity or selectivity of the reaction.     

Cycloaddition of nitrile oxides to substituted vinylphosphonates

Cycloaddition of nitrile oxides to substituted vinylphosphonates was performed. A series of 4,5‐dihydroisoxazoles containing phosphonyl group were synthesized under very mild condition in excellent regiospecificity. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:309–311, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10149     

Catalytic asymmetric three-component acyl-Strecker reaction

The first organocatalytic asymmetric three-component Strecker reaction, the urea-catalyzed acylcyanation of in situ generated imines, has been developed. Different alpha-amido nitriles are formed in excellent yields and enantioslectivities from aldehydes, amines, and acyl cyanides in the presence of Jacobsen's thiourea catalyst 5. Despite its obvious use for the synthesis of alpha-amino acids and their derivatives, our reaction may find use in diversity oriented synthesis and medicinal chemistry. [reaction: see text]     

Synthesis of substituted p-stereogenic vinylphosphine oxides by olefin cross-metathesis

[reaction: see text] Substituted vinylphosphine oxides have been prepared in good yield and exclusive (E)-olefin selectivity via olefin cross-metathesis using Grubbs and Hoveyda-type ruthenium catalysts. In addition, metathesis of chiral vinylphosphine oxides proceeds without racemization of the phosphorus chirality center, providing easy access to functionalized chiral nonracemic (E)-alkenylphosphine oxides.     

Catalytic asymmetric brominative dearomatization reaction of benzofurans

A catalytic asymmetric brominative dearomatization reaction of benzofuran derivatives was achieved by using hydroquinidine 1,4-phthalazinediyl diether [(DHQ)₂PHAL] as the catalyst and N-bromoacetamide (NBAc) as the brominating reagent. A series of brominated spiro[benzofuran-2,5'-oxazoles] bearing two contiguous stereogenic centers were obtained in high yields (up to 99%) with excellent enantioselectivity (up to 97% ee).     

Catalytic asymmetric intermolecular Stetter reaction of glyoxamides with alkylidenemalonates

An asymmetric intermolecular Stetter reaction of glyoxamide and alkylidenemalonates has been developed. Catalyzed by a novel N-heterocyclic carbene, the Stetter adducts are formed in good yield and excellent enantioselectivity. The presence of a sensitive epimerizable stereocenter is tolerated under these mildly basic reaction conditions if a bulky amine base is used. The products may be further elaborated to provide synthetically useful intermediates.     

Catalytic effect of nanosized metal oxides on the Hantzsch reaction

The effect of nanosized copper and aluminum oxides, which have a higher sorption capacity than that of bulk samples, on the Hantzsch reaction was studied. The adsorption of starting benzaldehydes and ethyl acetoacetate on the surface of copper and aluminum nanooxides resulted in the activation of these molecules and accelerated the Hantzsch reaction. In addition, considerable activation of ammonia and intermediates (chalcone and enamine) on the surface of aluminum nanooxide facilitated an increase in the rate and selectivity of the process. The experimental results were used to develop a one-pot method for the preparation of nifedipine and nitrendipine.     

Catalytic effect of nanosized metal oxides on the knoevenagel reaction

The effect of nanosized metal oxides (Al, Mg, Cu, Ni oxides) on the synthesis of chalcones that are key intermediate in the synthesis of Nitrendipine and Felodipine drugs was examined.     

Catalytic effect of nanosized metal oxides in the Biginelli reaction

The effect of nanosized metal oxides on the regio- and stereoselectivity of the multicomponent Biginelli reaction and the reaction mechanism under conditions of heterogeneous catalysis were studied. It was found that the considerable activation of reagents occurred on the surface of metal nanooxides. The Biginelli reaction occurred by two mechanisms: a carbocationic mechanism took place along with the generally accepted mechanism (through the N-acyliminium ion). Nanosized metal oxides in the presence of chiral inductors increased the regio- and stereoselectivity of the Biginelli reaction.     

Catalytic asymmetric nitroaldol (Henry) reaction with a zinc-Fam catalyst

Ferrocenyl-substituted aziridinylmethanol (Fam-1) was used as a catalyst with zinc for the asymmetric nitroaldol (Henry) reaction. This catalyst worked with a variety of aldehydes (aromatic, aliphatic, alpha,beta-unsaturated, and heteroaromatic) and alpha-ketoesters to give the nitroaldol product in up to 97% yield and 91% ee. The chiral ligand can be recovered and recycled without losing its activity.     

Catalytic asymmetric domino Michael addition-alkylation reaction: enantioselective synthesis of dihydrofurans

A catalytic enantioselective synthesis of dihydrofurans has been developed. 1,3-Dicarbonyl derivatives react with (E)-β,β-bromonitrostyrenes in the presence of a chiral bifunctional thiourea catalyst providing mild and efficient access to diverse polysubstituted dihydrofurans in good yields and enantioselectivities.     

Catalytic asymmetric weitz-scheffer reaction in the presence of bovine serum albumin

Epoxidation of 2-substituted 1,4-naphthoquinones with t-BuOOH or H₂O₂, in the presence of a catalytic amount of bovine serum albumin afforded the corresponding epoxynaphthoquinones in up 70% e.e.