Organocatalytic Michael Addition Research Articles

Organocatalytic Diastereo‐ and Enantioselective Michael Addition of α‐Aryl Isocyanoacetates to Aurone‐Derived Azadienes

AbstractA highly diastereo‐ and enantioselective organocatalytic Michael addition of α‐aryl isocyanoacetates to aurone‐derived azadienes under mild conditions has been developed. This efficient methodology enables access to chiral α,α‐disubstituted α‐amino ester derivatives with two adjacent stereocenters, one of them quaternary, bearing a benzofuran scaffold in their structure in high yields and stereocontrol. Furthermore, the reaction product can be readily converted into an α,α‐disubstituted α‐amino acid in high yield via hydrolysis of the isocyano group without compromising enantioselectivity.

Organocatalytic Michael Addition of Unactivated α-Branched Nitroalkanes to Afford Optically Active Tertiary Nitrocompounds.

The direct, asymmetric conjugate addition of unactivated α-branched nitroalkanes is developed based on the combined use of chiral amine/ureidoaminal bifunctional catalysts and a tunable acrylate template to provide tertiary nitrocompounds in 55-80% isolated yields and high enantioselectivity (e.r. up to 96:4). Elaboration of the ketol moiety in thus obtained adducts allows a fast entry to not only carboxylic and aldehyde derivatives but also nitrile compounds and enantioenriched 5,5-disubstituted γ-lactams.

Stereoselective synthesis of highly substituted 1-isomorphans (1-azabicyclo[3.3.1]nonanes).

We describe the first enantioselective synthesis of highly functionalized 1-azabicyclo[3.3.1]nonanes (1-IM). The 1-IM scaffold is present in natural products and drugs and is an isomer of the morphan moiety. The proposed methodology is based on an organocatalytic Michael addition of N-protected piperidine ketoesters to nitroalkenes and an intramolecular nitro-Mannich reaction as key transformations. The 1-IMs feature 6 contiguous stereocenters, substituents at positions 2 and 4, and nitro, ester, and hydroxyl functional groups at positions 3, 5, and 6 respectively. The synthesis is straightforward, highly stereoselective (up to 98% ee, >99 : 1 d.r.), with overall yields of up to 83% and requires only two purification steps.

Anti-Inflammatory Potentials of β-Ketoester Derivatives of N-Ary Succinimides: In Vitro, In Vivo, and Molecular Docking Studies

Inflammation, being a well-known and complex pathological condition, is always a challenge to the human health. This research work was designed for a rationale-based anti-inflammatory study on β-ketoester derivatives of N-ary succinimides. The compounds (A–D) were synthesized by organocatalytic Michael addition. The compounds were initially screened for in vitro 5-lipoxygenase (5-LOX) and cyclooxygenase (COX-2) assays. For the in vivo activity, carrageenan-induced paw edema and arachidonic acid-induced ear edema tests were used. Furthermore, different in vivo pathways such as prostaglandins E2, histamine, leukotriene, and bradykinin were studied. The results were supported with molecular docking studies. Among the compounds, D (ethyl 1-(1-benzyl-2,5-dioxopyrrolidin-3-yl)-2-oxocyclohexane-1-carboxylate) at a concentration of 1000 μg/ml showed significant inhibitory effects of 83.67% and 78.12% against COX-2 and 5-LOX in comparison to celecoxib and zileuton, respectively. Similarly, compound D also showed excellent in vivo anti-inflammatory potential. Amongst all the compounds, D demonstrated excellent (55.92 ± 2.95%) anti-inflammatory potential at maximum tested dose (100 mg/kg) which accomplished the highest significance at 4 h following the carrageenan insertion and stayed considerable ( ∗ ∗ ∗ P < 0.001 ) till the 5th hour of test sample injection. Compound D also exhibited excellent percent inhibition (63.81 ± 2.24%) at the highest dose in arachidonic acid-induced ear inflammation. On the basis of in vivo and in vitro results, compound D was subjected to various inflammation-causing agents such as histamine, prostaglandins E2, bradykinin, and leukotriene via the mouse paw edema test. Compound D revealed moderate effect (28.10 ± 1.64%) against histamine-induced paw edema while nonsignificant result (9.72 ± 3.125%) was marked for the bradykinin pathway. Compound D showed significance against edematogenic consequence of prostaglandin E2 (56.28–72.03%) and leukotriene (55.13 ± 2.25%) induced inflammation. In summary, our findings recommended that compound D possesses double acting anti-inflammatory properties inhibiting both COX and LOX pathways. Binding orientations and energy values computed via docking simulations support the results of the experimental in vitro evaluation.

Enantioselective Organocatalyzed Michael Addition of Isobutyraldehyde to Maleimides in Aqueous Media.

Thiourea was introduced into (R,R)-1,2-diphenylethylenediamine as an organocatalyst to promote the reaction between isobutyraldehydes and maleimides. Enantioselective Michael addition reaction was carried out as an eco-friendly method using water as the solvent. As a result of the reaction between isobutyraldehyde and maleimide, ≥97% yield and 99% enantioselectivity were obtained at a low catalyst loading of 0.01 mol%. The solvent effect can be explained by theoretical calculations that indicate the participation of a transition state, in which the CF3 substituent of the catalyst is a hydrogen bond activated by the surrounding water molecules. This discovery enabled the use of low catalyst loading in the organic reactions of chiral substances for pharmaceutical applications. Furthermore, a solvent effect for Michael reaction of the organocatalysts was proposed, and the organic reaction mechanisms were determined through quantum calculations.

Asymmetric organocatalytic Michael addition of cyclopentane-1,2-dione to alkylidene oxindole.

An asymmetric Michael reaction between cyclopentane-1,2-dione and alkylidene oxindole was studied in the presence of a multifunctional squaramide catalyst. Michael adducts were obtained in high enantioselectivities and in moderate diastereoselectivities.

Enantioselective Organocatalytic Michael Addition Reactions Catalyzed by Proline/Prolinol/Supported Proline based Organocatalysts: An Overview

AbstractEver since the discovery of enantioselective organocatalytic Michael addition reactions, it has emerged as a significant path for synthesizing a variety of stereochemical products under mild conditions, also a prominent C−X (X=C, O, N, S) bond formation reaction in organic chemistry. Over time, substantial progress has been accomplished in diversity‐ and target‐ oriented asymmetric Michael addition reactions. This review provides a brief overview of the results, scope, and limitations of several influential strategies involving enantio‐selective Michael addition reactions promoted by mono‐functional proline/prolinol/supported‐proline‐based chiral organocatalysts. Furthermore, we also sincerely believe that the various synthetic strategies documented in this review will pave a pathway to improve the status of Michael addition reactions for synthesizing various drug molecules involving complex intermediates.

Synthesis of Highly Functionalized Hydrindanes via Sequential Organocatalytic Michael/Mukaiyama Aldol Addition and Telescoped Hydrozirconation/Cross-Coupling as Key Steps: En Route to the AB System of Clifednamides.

The AB ring systems of the clifednamide family, polycyclic tetramate macrolactames (PoTeMs), were prepared by a new, convergent approach employing an intramolecular Diels-Alder (IMDA) reaction. Key steps comprise an organocatalytic Michael addition (>90% enantiomeric excess (ee)), a Mukaiyama aldol reaction for the convergent installation of a diene moiety, and a telescoped hydrozirconation/cross-coupling grafting an enone. The following IMDA furnished a highly functionalized hydrindane (diastereomeric ratio (dr) = 91:1) with the same configuration as the clifednamide scaffold. Advantages of this route are only one required protecting group, 13% overall yield over 9 steps (reduced from previously 17 steps/1.3% overall), and the potential access to the key intermediates in the clifednamide biosynthesis.

Recent Advances in Organocatalytic Asymmetric Michael Addition Reactions to α, β‐Unsaturated Nitroolefins

AbstractAn organocatalyzed asymmetric Michael addition reaction has been established as the most relevant and dynamic research area for the construction of chiral carbon‐carbon and carbon‐heteroatom bond. In the current scenario, rapid revolutions on asymmetric Michael addition to nitroolefins have been explored by taking advantage of newly developed chiral organocatalysts. Moreover, nitroolefins have proven as well‐known Michael acceptors for providing various structurally essential nitro‐functionalized frameworks. In addition to this, remarkable stereoselectivity has been achieved in this asymmetric process by following different mechanistic pathways that involve enamine, iminium ion intermediate formation and bifunctional H‐bonding interaction. So, we have discussed the recent advancements of organocatalytic Michael addition reactions to α, β‐unsaturated nitroolefins from the year 2016 to 2020.

Enantioselective Organocatalytic Michael Addition to Unsaturated Indolyl Ketones.

An efficient enantioselective organocatalytic method for the synthesis of N-alkylated indoles with α-branched alkyl substituents from the corresponding unsaturated indolyl ketones via a Michael addition has been developed. The resulting products were obtained in high enantioselectivities and in good yields. Various nucleophiles (nitroalkanes, malononitrile, malonic esters) can be used. The substitution pattern of the indole ring had no significant impact on the reaction outcome. Both electron-withdrawing and electron-donating substituents in any position of the heteroaromatic ring were well-tolerated.

Organo-catalyzed Michael addition of 2-fluoro-2-arylacetonitriles

An efficient synthesis of a variety of 2-arylacetonitriles containing a fluorinated stereogenic center through organo-catalyzed Michael addition reaction of 2-fluoro-2-arylacetonitriles has been developed. This protocol uses a cheap organocatalyst (DBU) and has a broad substrate scope: α, β-unsaturated ketones, esters, nitriles and sulfones were all successfully reacted. Importantly, water proved to be a good solvent for this reaction.

Organocatalyzed Michael Addition to Nitroalkenes via Masked Acetaldehyde

A novel and safe reaction protocol for the enantioselective enamine-catalysed addition of acetaldehyde to nitroalkenes is presented; this protocol makes use of a safe acetaldehyde precursor to access important intermediates to Active Pharmaceutical Ingredients (APIs), and allows the use of fewer equivalents of acetaldehyde and lower catalyst loadings. The reaction developed proved to be suitable to be performed on gram-scale and to produce key intermediates for the synthesis of pharmacologically active compounds such as pregabalin.

The Cyclohexa-2,5-dienyl Group as a Placeholder for Hydrogen: Organocatalytic Michael Addition of an Acetaldehyde Surrogate.

An aldehyde with a cyclohexa‐2,5‐dienyl group in the α‐position is introduced as a storable surrogate of highly reactive acetaldehyde. The cyclohexa‐2,5‐dienyl unit is compatible with an enantioselective Michael addition to nitroalkenes promoted by a Hayashi–Jørgensen catalyst and can be removed by a boron Lewis acid mediated C−C bond cleavage. The robust two‐step sequence does not require a large excess of the aldehyde component that is typically needed when directly using acetaldehyde.

Organocatalytic Michael Addition as a Method for Polyisobutylene Chain‐End Functionalization

Front Cover: In article number 2000382 Mohammed Al-Hashimi, Hassan S. Bazzi and co-workers adapt the organocatalyzed aza- and thiol-Michael addition ‘click’ reaction to polyisobutylene acrylate functionalization. This approach paves the way to a myriad of chain-end functional polyolefins with a broad range of potential applications.

Organocatalytic Michael Addition as a Method for Polyisobutylene Chain-End Functionalization.

Functionalization of polyolefins, in particular polyisobutylene, remains a relatively unexplored application for the Michael reaction. This work evaluates the potential of polyisobutylene acrylate (PIBA) chain-end modification via organocatalyzed thiol-Michael and aza-Michael additions. A series of chain-end functional polyisobutylene oligomers are prepared using "click" reactions of thiols or amines to PIBA in the presence of 0.02 equivalents of organocatalyst. Reaction kinetics and chain-end transformations are monitored using NMR spectroscopy and the macromolecular products are characterized by size exclusion chromatography. Further potential of this synthetic strategy is illustrated by thiol-Michael addition of thiols formed in situ via nucleophilic thiolactone ring opening. The obtained results provide an efficient method for the preparation of functional polyisobutylene oligomers that can be utilized in a broad range of potential applications.

Enantioselective Construction of Vicinal Sulfur‐functionalized Quaternary and Tertiary Stereocenters via Organocatalytic Michael Addition of 5H‐Thiazol‐4‐ones to 1‐Azadienes

AbstractAn organocatalytic enantioselective Michael addition of 5H‐thiazol‐4‐ones to 1‐azadienes has been developed. In the presence of chiral phosphoric acid, a series of optically active benzofuran derivatives featured by vicinal sulfur‐containing quaternary and tertiary stereocenters were obtained in high yields (71‐99%) with high stereoselectivities (70–96% ee and 8 : 1–20 : 1 d.r.).

Enantioselective Organocatalytic Michael Addition and Ring Closure Cascade Reaction of o‐Quinone Methides with Nitriles

A convenient way to prepare chiral 2-amino-3-substituted-4H-chromen derivatives.

Synthesis of Chiral 3,4‐Disubstituted Pyrrolidines with Antibacterial Properties

Chiral aliphatic heterocycles are important structural feature of many pharmaceutical agents. Antibiotic resistance is a serious medical problem, therefore new antibacterial compounds are urgently needed. Herein, we describe synthesis of a series of 3,4‐disubstituted pyrrolidine derivatives via organocatalytic Michael addition followed by reductive cyclization. These compounds inhibited growth of standard as well as methicillin‐resistant strains of Escherichia coli and Staphylococcus aureus.

Straightforward access to densely substituted chiral succinimides through enantioselective organocatalyzed Michael addition of α-alkyl-cyclic ketones to maleimides

A simple, cheap and unchanged organocatalytic system provides efficient access to densely substituted chiral succinimides bearing QCC–TCC vicinal stereocenters from unreactive α-alkyl cyclic ketones and maleimides.

Organocatalytic Michael Addition to (D)-Mannitol-Derived Enantiopure Nitroalkenes: A Valuable Strategy for the Synthesis of Densely Functionalized Chiral Molecules.

Carbohydrates are abundant renewable resources and are a feedstock for green chemistry and sustainable synthesis of the future. Among the hexoses and the pentoses present in biomass, mannitol was selected in the present project as a valuable platform, directly available from the chiral pool, to build highly functionalized molecules. Starting from (R)-2,3-O-cyclohexylidene glyceraldehyde, which is easily prepared in a large scale from D-mannitol, an enantiopure chiral nitro alkene was prepared by reaction with nitromethane, and its reactivity studied. Organocatalytic Michael addition of dimethyl malonate, β-keto esters, and other nucleophiles on the nitro alkene afforded high stereoselectivity and densely functionalized chiral molecules, which were further synthetically developed, leading to five-membered lactones and bicyclic lactams. Preliminary studies showed that the metal-free catalytic reaction on the chiral nitro alkene can be performed under continuous flow conditions, thus enabling the use of (micro)mesofluidic systems for the preparation of enantiomerically pure organic molecules from the chiral pool.