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A simple bioinspired ortho-quinone catalyst for the aerobic oxidative dehydrogenation of amines to imines is reported. Without any metal cocatalysts, the identified optimal ortho-quinone catalyst enables the oxidations of α-branched primary amines and cyclic secondary amines. Mechanistic studies have disclosed the origins of different performances of ortho-quinone vs para-quinone in biomimetic amine oxidations.

The first effective example of asymmetric conjugate addition-protonation reactions of thiols to α-substituted vinyl ketones by chiral primary amine catalysis is reported. A simple chiral primary-tertiary diamine catalyst derived from l-phenylalanine was found to promote the sulfa-Michael addition-protonation reactions with good to excellent enantioselectivity.

This paper describes a simple chiral primary amine-catalyzed highly efficient and practical protocol for the synthesis of both Wieland-Miescher ketone and Hajos-Parrish ketone as well as their analogues. The reaction can be conducted in gram scale with 1% mol catalyst loading producing high enantioselectivity (up to 96% ee) and excellent yields (up to 98%). This procedure represents one of the most efficient methods for the synthesis of these versatile chiral building blocks.

The current work reports an organocatalytic strategy for the asymmetric catalysis of chiral benzofuran-2(3H)-ones bearing 3-position all-carbon quaternary stereocenters. Accordingly, highly enantioselective Michael addition reactions of 3-substituted benzofuran-2(3H)-ones to nitroolefins have been developed by utilizing a bifunctional tertiary-amine thiourea catalyst. The reactions accommodate a number of nitroolefins and 3-substituted benzofuran-2(3H)-ones to give the desired chiral benzofuran-2(3H)-one products with moderate to excellent yields (up to 98%) and moderate to very good selectivities (up to 19 : 1 dr and up to 91% ee). Theoretical calculations using the DFT method on the origin of the stereoselectivity were conducted. The effect of the nitroolefin substituent position on the stereoselectivity of the Michael addition reaction was also theoretically rationalized.

A new approach of asymmetric supramolecular catalysis has been developed by combining the supramolecular recognition of beta-cyclodextrin (beta-CD) and the superior property of a chiral primary amine catalyst. The resulted beta-CD enamine catalysts could effectively promote asymmetric direct aldol reactions with excellent enantioselectivity in an aqueous buffer solution (pH = 4.80). The identified optimal catalyst CD-1 shows interesting characteristics of supramolecular catalysis with selective recognition of aldol acceptors and donors. A detailed mechanistic investigation on such supramolecular catalysis was conducted with the aid of NMR, fluorescence, circular dichroism, and ESI-MS analysis. It is revealed that the reaction is initialized first by binding substrates into the cyclodextrin cavity via a synergistic action of hydrophobic interaction and noncovalent interaction with the CD-1 side chain. A rate-limiting enamine forming step is then involved which is followed by the product-generating C-C bond formation. A subsequent product release from the cavity completes the catalytic cycle. The possible connections between molecular recognition and asymmetric catalysis as well as their relevance to enamine catalysis in both natural enzymes and organocatalysts are discussed based on rational analysis.

An asymmetric direct aldol reaction of acetoacetals is described. Under the catalysis of a simple chiral primary amine, the direct aldol reactions of acetoacetals occur exclusively on the gamma-position to give vinylogous-type aldol products with high diastereo- and enantioselectivity.

We present herein simple primary-tertiary diamine-Brønsted acid conjugates that catalyze both syn- and anti-aldol reactions of dihydroxyacetones (DHAs) with high diastereoselectivities and enantioselectivities. This type of organocatalysts functionally mimics all four DHA aldolases, namely L-fuculose-1-phosphate aldolase, D-tagatose-1,6-diphosphate aldolase, D-fructose-1,6-diphosphate aldolase, and L-rhamnulose-1-phosphate aldolase.

A new strategy for the immobilization of asymmetric organocatalysts by combining polystyrene (PS)/sulfonic acids and chiral amines in situ through acid-base interactions is presented. The PS/sulfonic acids play a dual role as catalyst anchors and modulators for activity and stereoselectivity. Different types of polymeric sulfonic acids were examined and 1% divinylbenzene (DVB) cross-linked PS/sulfonic acid 1 e with a medium loading of sulfonic acid moieties was found to be the optimal support. Furthermore, the noncovalency of this system allows combinatorial screening of optimal catalysts for the targeted reactions. In this regard, highly efficient and enantioselective heterogeneous catalysts were identified for the asymmetric direct aldol and Michael addition reactions. The catalysts could be easily recovered by filtration and reused for six cycles with similar stereoselectivity but slightly decreased activity. Significantly, the deactivated catalysts could be regenerated following an acidic washing/amine recharging procedure.

Chiral amine and polyoxometalate (POM) acids were combined to give highly efficient, stereoselective, and recoverable enamine-based catalysts. Less than 1 mol % of chiral amine loading was sufficient for good catalytic activity, and the catalyst could be recovered and reused 6 times with unchanged enantioselectivity and slightly decreased activity.

A highly predictive model to correlate the steric and electronic parameters of tertiary amine thiourea catalysts with the stereoselectivity of Michael reactions of 3-substituted benzofuranones and alkyl 2-phthalimidoacrylates is described. As predicted, new 3,5-bis(trifluoromethyl)benzyl- and methyl-substituted tertiary amine thioureas turned out to be highly suitable catalysts for this reaction and enabled the synthesis of enantioenriched α-amino acid derivatives with 1,3-nonadjacent stereogenic centers. [ABSTRACT FROM AUTHOR]

Enantioselective protonation with a catalytic enamine intermediate represents a challenging, yet fundamentally important process for the synthesis of α-chiral carbonyls. We describe herein chiral primary-amine-catalyzed conjugate additions of indoles to both α-substituted acroleins and vinyl ketones. These reactions feature enamine protonation as the stereogenic step. A simple primary-tertiary vicinal diamine 1 with trifluoromethanesulfonic acid (TfOH) was found to enable both of the reactions of acroleins and vinyl ketones with good activity and high enantioselectivity. Detailed mechanistic studies reveal that these reactions are rate-limiting in iminium formation and they all involve a uniform H2O/acid-bridged proton transfer in the stereogenic steps but divergent stereocontrol modes for the protonation stereoselectivity. For the reactions of α-branched acroleins, facial selections on H2O-bridged protonation determine the enantioselectivity, which is enhanced by an OH⋅⋅⋅π interaction with indole as uncovered by DFT calculations. On the other hand, the stereoselectivity of the reactions with vinyl ketones is controlled according to the Curtin-Hammett principle in the CC bond-formation step, which precedes a highly stereospecific enamine protonation. [ABSTRACT FROM AUTHOR]

Magnetic polyoxometalates (POMs) are obtained by a simple sonication between functionalized magnetic nanoparticles and polyoxometalates. This material can be used not only as a highly active acid catalyst, but also as a catalyst support for chiral amines. [ABSTRACT FROM AUTHOR]

A series of primary-tertiary diamine catalysts were designed and synthesized from primary natural amino acids. Application of these new chiral catalysts in direct aldol reactions of a-hydroxyketones showed very good catalytic activity (up to 97% yield) and high syn selectivity (up to synl anti = 30:1, 99% ee). [ABSTRACT FROM AUTHOR]

A highlyenantioselective Diels–Alder reaction of 3-olefinicbenzofuran-2-ones with polyenals catalyzed by diphenylprolinolsilylether through a trienamine activation strategy was developed. [ABSTRACT FROM AUTHOR]

A highly enantioselective Michael–aldol tandem reaction with respect to prochiral 2-substituted benzofuran-3-ones and enones by a facile primary amine catalyst was investigated. The approach provides rapid access to the desired pharmaceutically active griseofulvin analogues. [ABSTRACT FROM AUTHOR]

The aerobic oxidative dehydrogenation of α-branched primary amines and cyclic secondary amines to imines without any metal cocatalyst is presented [ABSTRACT FROM AUTHOR]

The article presents chemical equations for the article "Asymmetric Sulfa-Michael Addition to α-Substituted Vinyl Ketones Catalyzed by Chiral Primary Amine" by L. Zhang and others published in "Organic Letters" in 2014.

N,N-Dimethylethylenediamine·TfOH is found to be an efficient catalyst for the direct α-allylic alkylation of unmodified aldehydes with allylic alcohols. [ABSTRACT FROM AUTHOR]

The first example of the enantioselective conjugate addition of alkenes to enones, catalyzed by chiral primary amines are reported.The reaction is enabled by chiral primary amines through a typical iminium ion cycle. [ABSTRACT FROM AUTHOR]