New Class Of Organocatalysts Research Articles

ChemInform Abstract: Chiral Quaternary Phosphonium Salts: A New Class of Organocatalysts

AbstractReview: 50 refs.

Chiral microspheres constructed by helical substituted polyacetylene: A new class of organocatalyst toward asymmetric catalysis

This article reports the first microspheres consisting of helical substituted polyacetylene and showing interesting asymmetric catalysis ability. For preparing such chiral microspheres, two acetylene-based monomers, M1L with l-proline pendant group and MA, underwent precipitation copolymerization in the presence of rhodium catalyst in a solvent mixture of butanone/n-heptane. Regular microspheres (approx. 1μm in diameter) were successfully prepared under suitable conditions. According to CD and UV spectroscopy measurements, the microspheres exhibit considerable optical activity, resulting from the substituted polyacetylene chains adopting helical structures of preferred one-handed screw sense. The microspheres were used as a chiral organocatalyst to heterogeneously catalyze the asymmetric Aldol reaction of p-nitrobenzaldehyde and cyclohexanone in aqueous media. Remarkable catalytic efficiency was obtained (yield 76% and ee 80%). After catalysis, the microspheres can be easily recovered. The methodology created in this study provides opportunities for developing a new class of chiral polymer organocatalyst.

ChemInform Abstract: Chiral Dihydrobenzo[1,4]oxazines as Catalysts for the Asymmetric Transfer‐Hydrogenation of α,β‐Unsaturated Aldehydes.

AbstractA new class of organocatalysts based on 2,3‐dihydrobenzo[1,4]oxazine is prepared and applied in the enantioselective hydrogenation of α,β‐unsaturated aldehydes (I) giving the corresponding saturated aldehydes bearing a stereogenic center with two different aryl groups with high enantioselectivities.

Chiral quaternary phosphonium salts: a new class of organocatalysts

Phase-transfer catalysis has widely been used as a prime synthetic tool for both laboratory and industrial processes. During the last twenty years, asymmetric phase-transfer catalysis using chiral organocatalysts has attracted widespread interest. However, the scope of chiral phase-transfer catalysis has been limited mostly to the quaternary ammonium salts. As an emerging area, the recent developments in the application of quaternary phosphonium salts as chiral phase-transfer catalysts are discussed in this article.

Chiral dihydrobenzo[1,4]oxazines as catalysts for the asymmetric transfer-hydrogenation of α,β-unsaturated aldehydes

A new class of organocatalysts based on the structure of 2,3-dihydrobenzo[1,4]oxazine was prepared and applied in the enantioselective transfer-hydrogenation of α,β-unsaturated aldehydes with Hantzsch ester as hydride donor. These catalysts proved to be particularly effective for the conjugate reduction of β,β-diaryl-substituted acrylaldehydes leading to saturated aldehydes bearing a stereogenic center with two different aryl groups with enantioselectivities of up to 91% ee.

Development of an N-sulfinyl prolinamide for the asymmetric aldol reaction

A new class of organocatalysts is reported that incorporates an N-sulfinyl amide in place of the carboxylic acid of proline to serve as a hydrogen bond donor, chiral directing group, and solubilizing element. The successful application of this type of catalyst to the asymmetric aldol reaction of acetone and aryl aldehydes, for which proline performs poorly, is also described.

One-step, efficient synthesis of combined threonine–surfactant organocatalysts for the highly enantioselective direct aldol reactions of cyclic ketones with aromatic aldehydes in the presence of water

In this work, a new class of organocatalysts have been designed and synthesized in one step by a rational combination of threonine with acyl chlorides at room temperature in trifluoroacetic acid to make a series of novel combined threonine-surfactant organocatalysts readily available on a large-scale. No protecting groups or chromatographic techniques are involved in the procedures, while certain combined threonine-surfactant organocatalysts mediate the direct aldol reactions of cyclic ketones with aromatic aldehydes to provide the aldol products in good yields with enantioselectivities of up to 99%.

ChemInform Abstract: Pyrrolidinyl—Camphor Derivatives as a New Class of Organocatalyst for Direct Asymmetric Michael Addition of Aldehydes and Ketones to β‐Nitroalkenes.

AbstractThe synthetical utility is demonstrated by the synthesis of a tetrasubstituted (XIX) starting from (S)‐citronellal (XVII) with high selectivity.

ChemInform Abstract: Pyrrolidinyl-Camphor Derivatives as a New Class of Organocatalyst for Direct Asymmetric Michael Addition of Aldehydes and Ketones to β-Nitroalkenes.

ChemInform Abstract: Pyrrolidinyl-Camphor Derivatives as a New Class of Organocatalyst for Direct Asymmetric Michael Addition of Aldehydes and Ketones to β-Nitroalkenes.

Pyrrolidinyl–Camphor Derivatives as a New Class of Organocatalyst for Direct Asymmetric Michael Addition of Aldehydes and Ketones to β‐Nitroalkenes

Practical and convenient synthetic routes have been developed for the synthesis of a new class of pyrrolidinyl-camphor derivatives (7 a-h). These novel compounds were screened as catalysts for the direct Michael addition of symmetrical alpha,alpha-disubstituted aldehydes to beta-nitroalkenes. When this asymmetric transformation was catalyzed by organocatalyst 7 f, the desired Michael adducts were obtained in high chemical yields, with high to excellent stereoselectivities (up to 98:2 diastereomeric ratio (d.r.) and 99 % enantiomeric excess (ee)). The scope of the catalytic system was expanded to encompass various aldehydes and ketones as the donor sources. The synthetic application was demonstrated by the synthesis of a tetrasubstituted-cyclohexane derivative from (S)-citronellal, with high stereoselectivity.

Design, synthesis, and application of chiral electron-poor guanidines as hydrogen-bonding catalysts for the Michael reaction

The first chiral electron-poor guanidine organocatalysts were synthesized. The presence of a tunable electron-withdrawing group on the guanidine moiety allows for the modulation of the catalysts’ activity. The application of this new class of organocatalysts to the Michael reaction is demonstrated.

Rational Combination of Two Privileged Chiral Backbones: Highly Efficient Organocatalysts for Asymmetric Direct Aldol Reactions between Aromatic Aldehydes and Acylic Ketones

A new class of organocatalysts has been designed by rational combination of proline with cinchona alkaloids. The chiral amine 3a, prepared from l-proline and cinchonidine, has been found to be an efficient catalyst for the direct aldol reactions of acetone or 2-butanone with a wide range of aldehydes (up to 98% ee). The cinchonidine backbone is essential to the reaction efficiency and enantioselectivity.

Enantioselective Aza-Henry Reaction with an N-Sulfinyl Urea Organocatalyst

A new class of organocatalyst has been developed that incorporates a sulfinyl group as a urea or thiourea substituent. The sulfinyl group serves to simultaneously acidify the urea and provide asymmetric induction in hydrogen-bond-catalyzed reactions. The utility of this new catalyst structure is demonstrated by the high selectivity provided in the aza-Henry reaction not only for aromatic N-Boc imine substrates but also for aliphatic imines for which enantioselective H-bonding catalysis has not previously been demonstrated.

Benzimidazole‐pyrrolidine/H+ (BIP/H+), a Highly Reactive Organocatalyst for Asymmetric Processes

AbstractA new chiral benzimidazole‐pyrrolidine has been devised, which exhibits excellent activities in aminocatalyzed aldol reactions, leading to aldol products in high yields and enantioselectivities in the presence of an equimolar amount of a Brönsted acid. This organocatalyst has demonstrated remarkable reactivities in aldol processes even with equimolar amounts of aldehyde and ketone in THF. A discussion of the role of the Brönsted acid as a co‐catalyst is provided along with some applications of this new class of organocatalyst in Robinson annelation and α‐amination processes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

3,3′‐Bimorpholine Derivatives as a New Class of Organocatalysts for Asymmetric Michael Addition.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Asymmetric organocatalysis with glycosyl-β-amino acids: direct asymmetric aldol reaction of acetone with aldehydes

Direct asymmetric aldol reaction of acetone with aromatic aldehydes was achieved in good yields and high enantioselectivity using 5-amino-5-deoxy-β- l- ido-(α- d- gluco)-heptofuranuronic acids as a new class of organocatalysts.

3,3‘-Bimorpholine Derivatives as a New Class of Organocatalysts for Asymmetric Michael Addition

New N-alkyl-3,3'-bimorpholine derivatives (iPBM) were revealed to be efficient organocatalysts for the asymmetric direct Michael addition of aldehydes to nitroolefins and a vinyl sulfone. In these transformations using iPBM, 1,4-adducts were afforded in high yields, with good to high levels of diastereo- and enantioselectivity. The stereochemical outcome of the reaction could be explained by an acyclic synclinal model. [reaction: see text]

The Use of N-iPr-2,2'-bipyrrolidine Derivatives as Organocatalysts for Asymmetric Michael Additions

The recent rapid growth of organocatalysis has shown a new approach in organic chemistry and presents the obvious advantage in the avoidance of expensive and often toxic metals. Moreover, the organocatalysts are generally easier to make than standard catalytic reagents. Therefore, our laboratory has synthesized N-alkyl-2,2'bipyrrolidine derivatives as a new class of organocatalysts and applied them to the asymmetric Michael addition of ketones and aldehydes to nitroolefins via an enamine intermediate. We have furthermore developed the first asymmetric Michael addition of aldehydes to vinyl sulfones catalyzed with our diamines. The 1,4 adducts are obtained in good yields with enantioselectivities up to 80% ee. The determination of absolute configuration allowed us to postulate a Si,Si transition state model, as described previously for nitroolefins.