Primary Amine Thiourea Research Articles

Synthesis of D-Fructose-Based Bifunctional Primary Amine-Thiourea Organocatalysts and Their Applications in Asymmetric Reactions

The preparation of a new class of six bifunctional thiourea organocatalysts having a D-fructose scaffold and a primary amino group was demonstrated. In the present study, the novel organocatalysts exhibited excellent enantio- and moderate diastereoselectivities in the asymmetric Michael addition of aliphatic ketones and 1,3-diketone to substituted nitroolefins at room temperature. In addition, the direct asymmetric aldol reaction between cyclic aliphatic ketone and aromatic aldehydes was also studied in the presence of the saccharide-thiourea organocatalysts giving excellent yield with moderate enantioselectivity.

Asymmetric Alkylation of Cyclic Ketones with Dehydroalanine via H-Bond-Directing Enamine Catalysis: Straightforward Access to Enantiopure Unnatural α-Amino Acids.

The growing importance of structurally diverse and functionalized enantiomerically pure unnatural amino acids in the design of drugs, including peptides, has stimulated the development of new synthetic methods. This study reports the challenging direct asymmetric alkylation of cyclic ketones with dehydroalanine derivatives via a conjugate addition reaction for the synthesis of enantiopure ketone-based α-unnatural amino acids. The key to success was the design of a bifunctional primary amine-thiourea catalyst that combines H-bond-directing activation and enamine catalysis. The simultaneous dual activation of the two relatively unreactive partners, confirmed by mass spectrometry studies, results in high reactivity while securing high levels of stereocontrol. A broad substrate scope is accompanied by versatile downstream chemical modifications. The mild reaction conditions and consistently excellent enantioselectivities (>95 % ee in most cases) render this protocol highly practical for the rapid construction of valuable noncanonical enantiopure α-amino-acid building blocks.

Primary amine–thiourea grafted graphene–based heterogeneous chiral catalysts for highly enantioselective Michael additions

Heterogeneous asymmetric catalysis based on earth-abundant carbon materials put together the advantages for the ease of separation, simple regeneration, and high stability of solid catalysts as well as acts as low-cost, environmentally friendly metal-free alternative to the metal-based catalysts. Two new bifunctional carbocatalysts [(S,S) and (R,R) GO-PATU] were prepared by anchoring enantiomerically pure organosilanes bearing primary amine and thiourea groups to the graphene oxide (GO) skeleton covalently via silane coupling reaction. The surface modification of GO was analyzed by a combination of Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron spectroscopy (TEM) techniques. The catalytic performances of graphene-based materials were investigated in the asymmetric Michael addition reactions of α,α-disubstituted-aldehydes to nitrostyrenes and N-substituted-maleimides. The effects of solvents and Brønsted basic or acidic additives were evaluated using both catalysts and good yields (up to 85%) and stereoselectivities (up to 95% ee) were obtained in dichloromethane at room temperature in the presence of l- and d-camphorsulfonic acid. Besides, recycling and reusing studies of the catalysts were successfully performed.

A versatile approach to functionalized cyclic ketones bearing quaternary carbon stereocenters via organocatalytic asymmetric conjugate addition of nitroalkanes to cyclic β-substituted α,β-Enones

Abstract A versatile organocatalytic asymmetric conjugate addition of nitroalkanes to β-substituted cyclic α,β-enones to yield cyclic ketones bearing all-carbon quaternary stereogenic centers at β-C has been developed. This is an extension of the method that we developed during the total synthesis of (−)-haliclonin A, which features the employment of structurally relatively simple, cheap and easily available primary amine-thiourea derived from (R,R)-1,2-diaminocyclohexane as the chiral catalyst. The method shows wide substrate scope, good functional group tolerance, which allows a quick access to multi-functionalized chiral compounds. The synthetic potential of the method was demonstrated by one-step transformations of the nitro-ketone adducts to four other classes of compounds. The absolute configurations of adducts were determined by comparison of both the retention time of chiral HPLC analysis and sense of specific optical rotation with those of a known compound. The enantioselective control mechanism was rationalized based on the DFT computational studies.

Design and Synthesis of a Novel Primary Amine-Thiourea Organocatalyst Based on Unactivated C(sp3)-H Amination Reaction

Design and Synthesis of a Novel Primary Amine-Thiourea Organocatalyst Based on Unactivated C(sp3)-H Amination Reaction

Solvent-Free Enantioselective Michael Reactions Catalyzed by a Calixarene-Based Primary Amine Thiourea.

An upper-rim functionalized calix[4]arene-based thiourea installed onto the ( R, R)-1,2-cyclohexanediamine scaffold was synthesized with a view to investigate its catalytic ability in enantioselective Michael additions. The reactions were found to conveniently proceed under solvent-free conditions, observing good to high enantioselectivities. From this preliminary study, the calix[4]arene unit is likely to play a role in affecting the conversion and to a lesser extent to the stereochemical outcome of the reactions through van der Waals contacts and C-H···π interactions with the substrates.

13 C Kinetic Isotope Effects as a Quantitative Probe To Distinguish between Enol and Enamine Mechanisms in Aminocatalysis.

A combination of experimental 13 C kinetic isotope effects (KIEs) and high-level density functional theory (DFT) calculations is used to distinguish between "enamine" and "enol" mechanisms in the Michael addition of acetone to trans-β-nitrostyrene catalyzed by Jacobsen's primary amine thiourea catalyst. In light of the recent findings that the widely used 18 O-incorporation probe for these mechanisms is flawed, the results described in this communication demonstrate an alternative probe to distinguish between these pathways. A key advantage of this probe is that quantitative mechanistic information is obtained without modifying experimental conditions. This approach is expected to find application in resolving mechanistic debates, while providing valuable information about the key transition state of organocatalyzed reactions involving the α-functionalization of carbonyls.

Concentration Effect in the Asymmetric Michael Addition of Acetone to β-Nitrostyrenes Catalyzed by Primary Amine Thioureas

Bifunctional primary amine thiourea (PAT) organocatalysts show remarkable improvement in enantioselectivity and catalytic activity (turnover frequency) in the asymmetric Michael addition of acetone to β-nitrostyrenes upon dilution. Mechanistic investigations indicate that this behavior corresponds to the inhibition of off-cycle catalyst deactivation at low concentration, rather than to the operation of aggregation phenomena at high concentration. Reaction at low concentration (≤0.2 M in β-nitrostyrene) leads to the minimization of catalyst deactivation and, thus, to the optimization of yield and ee of the Michael­ addition products.

Construction of Furan Derivatives with a Trifluoromethyl Stereogenic Center: Enantioselective Friedel-Crafts Alkylations via Formal Trienamine Catalysis.

An asymmetric Friedel-Crafts alkylation reaction of 2-furfuryl ketones with β-trifluoromethyl enones has been developed via formal trienamine catalysis of a bifunctional primary amine-thiourea substance derived from L-tert-leucine, delivering the furan derivatives incorporating a stereogenic trifluoromethyl (CF3) group in good to high yields with excellent enantioselectivity.

Highly Enantioselective Michael Addition of Aromatic Ketones to Nitrodienes and the Application to the Synthesis of Chiral γ-Aminobutyric Acid

A highly enantioselective Michael addition of aromatic ketones to α,β,γ,δ-unsaturated nitro compounds is described. In the presence of a chiral primary amine-thiourea based on dehydroabietic amine, γ-nitro ketones were obtained in excellent enantioselectivities (up to 95% ee) with up to 95% yield. In addition, this methodology has been successfully applied in the asymmetric synthesis of chiral 3-(aminomethyl)-5-phenylpentanoic acid.

(Thio)urea-mediated synthesis of functionalized six-membered rings with multiple chiral centers.

Organocatalysis, now running its second decade of life, is being considered one of the main tools a synthetic chemist has to perform asymmetric catalysis. In this review the synthesis of six-membered rings, that contain multiple chiral centers, either by a ring closing process or by a functionalization reaction on an already existing six-membered ring, utilizing bifunctional (thio)ureas will be summarized. Initially, the use of primary amine-thioureas as organocatalysts for the above transformation is being discussed, followed by the examples employing secondary amine-thioureas. Finally, the use of tertiary amine-thioureas and miscellaneous examples are presented.

ChemInform Abstract: (Thio)urea‐Mediated Synthesis of Functionalized Six‐Membered Rings with Multiple Chiral Centers

AbstractReview: [97 refs.

Highly enantioselective Michael addition of α,α-disubstituted aldehydes to nitroolefins

A highly enantioselective Michael addition reaction of α,α-disubstituted aldehydes to β-nitrostyrenes has been developed. In the presence of rosin-based chiral primary amine-thiourea, γ-nitroaldehydes were afforded in excellent enantioselectivities (up to 99 % ee) with up to 99 % yield.

Deciphering the roles of multiple additives in organocatalyzed Michael additions.

The synergistic effects of multiple additives (water and acetic acid) on the asymmetric Michael addition of acetone to nitrostyrene catalyzed by primary amine-thioureas (PAT) were precisely determined. Acetic acid facilitates hydrolysis of the imine intermediates, thus leading to catalytic behavior, and minimizes the formation of the double addition side product. In contrast, water slows down the reaction but minimizes catalyst deactivation, eventually leading to higher final yields.

Catalytic Asymmetric Formal Aza-Diels–Alder Reactions of α,β-Unsaturated Ketones and 3H-Indoles

Asymmetric formal aza-Diels–Alder reactions with α,β-unsaturated ketones and 3H-indoles with disubstituted groups on the C3 position catalyzed by primary amine-thiourea bifunctional catalyst have been developed. The reactions produced chiral hexahydropyrido-[1,2-a]-indole-2-ones in high yields with excellent diastereo- and enantioselectivities.

Highly Enantioselective Michael Addition of Nitroalkanes to Enones and Its Application in Syntheses of (R)-Baclofen and (R)-Phenibut

A highly enantioselective Michael addition of nitroalkanes to α,β-unsaturated ketones was developed. In the presence of a chiral primary amine–thiourea catalyst based on dehydroabietic amine, γ-nitro ketones were obtained with excellent enantioselectivities (up to 99% ee) and in up to 96% yield. This protocol was successfully applied in asymmetric syntheses of (<i>R</i>)-baclofen and (<i>R</i>)-phenibut with high yields and excellent enantioselectivities.

ChemInform Abstract: Enantioselective Direct Bisvinylogous 1,6‐Additions of β‐Allyl‐2‐cyclohexenone to α,α‐Dicyanodienes Through Trienamine Catalysis.

An asymmetric direct ϵ-regioselective bisvinylogous 1,6-addition reaction of β-allyl-2-cyclohexenone to β-substituted α,α-dicyanodienes was developed through trienamine catalysis of a bifunctional primary amine–thiourea compound. Excellent enantioselectivity (up to 97 % ee) was obtained even through such a remote reaction mode. In addition, more complex cyclic frameworks could be efficiently constructed with high stereoselectivity.

ChemInform Abstract: New Simple Primary Amine—Thiourea Organocatalysts and Their Application in Asymmetric Conjugate Addition.

Abstract1‐((1R,2R)‐2‐aminocyclohexyl)‐3‐(9H‐fluoren‐9‐yl)thiourea in combination with 4‐methylbenzoic acid as additive catalyzes the reaction of 2‐aryl‐1‐nitroethylenes (I) with acetone (II) to give 4‐aryl‐2‐oxo‐5‐nitropentanes (III) in moderate yields and with good enantioselectivities.

Enantioselective Direct Bisvinylogous 1,6‐Additions of β‐Allyl‐2‐cyclohexenone to α,α‐Dicyanodienes through Trienamine Catalysis

AbstractAn asymmetric direct ϵ‐regioselective bisvinylogous 1,6‐addition reaction of β‐allyl‐2‐cyclohexenone to β‐substituted α,α‐dicyanodienes was developed through trienamine catalysis of a bifunctional primary amine–thiourea compound. Excellent enantioselectivity (up to 97 % ee) was obtained even through such a remote reaction mode. In addition, more complex cyclic frameworks could be efficiently constructed with high stereoselectivity.

New simple primary amine–thiourea organocatalysts and their application in asymmetric conjugate addition

A kind of simple primary amine–thiourea organocatalysts was developed. And their application in asymmetric conjugate addition of ketone to nitroalkene was investigated. In the presence of the new primary amine–thiourea, the conjugate addition of ketone to nitroalkene proceeded smoothly to afford the 1,4-adducts in high yields with good enantioselectivities.