Weinreb Amides Research Articles

Weinreb Amide as Secondary Station for the Dibenzo‐24‐crown‐8 in a Molecular Shuttle

Here is reported the synthesis of a new molecular shuttle: it consists of a dibenzo‐24‐crown‐8 (DB24C8) that surrounds a molecular axle containing an ammonium group and a newly considered Weinreb amide as stations. At the protonated state the DB24C8 is localized around the best ammonium station, while deprotonation‐carbamoylation of the ammonium triggers the shuttling of the macrocycle around the Weinreb amide site. Further post‐interlocking modification of the [2]rotaxane was attempted through the cleavage of the Weinreb amide bond using a Grignard reagent. While the non‐interlocked molecular axle was cleaved after a short time in mild conditions, the Weinreb amide bond remained unaltered in the [2]rotaxane species over time, even in the presence of a larger amount of Grignard and at a higher temperature, highlighting the protection shield of the macrocycle around the encircled axle.

Reusable and highly enantioselective water-soluble Ru(II)-Amm-Pheox catalyst for intramolecular cyclopropanation of diazo compounds.

A reusable and highly enantioselective catalyst for the intramolecular cyclopropanation of various diazo ester and Weinreb amide derivatives was developed. The reactions catalyzed by a water-soluble Ru(II)-Amm-Pheox catalyst proceeded smoothly at room temperature, affording the corresponding bicyclic cyclopropane ring-fused lactones and lactams in high yields (up to 99%) with excellent enantioselectivities (up to 99% ee). After screening of various catalysts, the Ru(II)-Amm-Pheox complex having an ammonium group proved to be crucial for the intramolecular cyclopropanation reaction in a water/ether biphasic medium. The water-soluble catalyst could be reused at least six times with little loss in yield and enantioselectivity.

Highly Regioselective Remote Lithiation of Functionalized 1,3-bis-Silylated Arenes.

Substituted arenes flanked by two bulky triethylsilyl groups were regiospecifically lithiated at the 5-position with nBuLi⋅PMDTA at 25 °C. The resulting aryllithiums reacted with a broad range of electrophiles such as ketones, isocyanates, Weinreb amides, allyl bromides, and CO2 at 25 °C. These bis-silylated arenes were then converted in simple reaction sequences into silyl-free tetrasubstituted arenes. This remote lithiation was extended to 2,6-bis(triethylsilyl)pyridine as well as 3,3'-bis(triethylsilyl)biphenyl.

Asymmetric Total Synthesis of Brasilicardins

Brasilicardins, bacterial diterpenoid natural products that display highly potent immunosuppressive activity, are promising immunosuppressant drug candidates. Structurally, they can be described as hybrids of terpenoids, amino acids, and saccharides, and share a characteristic highly strained anti-syn-anti-fused perhydrophenanthrene terpenoid scaffold (ABC-ring system) with two quaternary asymmetric carbon atoms. A unified and stereoselective total synthesis of all four brasilicardins has been designed based on the strategic use of an intramolecular conjugate addition. The ABC-ring system was initially constructed with high stereocontrol by novel intramolecular conjugate additions of Weinreb amides and in situ generated (Z)-vinyl copper species. The late-stage common intermediate was subjected to stereoselective installation of the amino acid component, followed by introduction of the saccharide unit via glycosylation to accomplish the total synthesis of brasilicardins A-D. Our synthesis offers opportunities to synthesize various brasilicardin analogues for biological and pharmacological investigations.

Asymmetric Total Synthesis of Brasilicardins

AbstractBrasilicardins, bacterial diterpenoid natural products that display highly potent immunosuppressive activity, are promising immunosuppressant drug candidates. Structurally, they can be described as hybrids of terpenoids, amino acids, and saccharides, and share a characteristic highly strained anti‐syn‐anti‐fused perhydrophenanthrene terpenoid scaffold (ABC‐ring system) with two quaternary asymmetric carbon atoms. A unified and stereoselective total synthesis of all four brasilicardins has been designed based on the strategic use of an intramolecular conjugate addition. The ABC‐ring system was initially constructed with high stereocontrol by novel intramolecular conjugate additions of Weinreb amides and in situ generated (Z)‐vinyl copper species. The late‐stage common intermediate was subjected to stereoselective installation of the amino acid component, followed by introduction of the saccharide unit via glycosylation to accomplish the total synthesis of brasilicardins A–D. Our synthesis offers opportunities to synthesize various brasilicardin analogues for biological and pharmacological investigations.

Palladium-Catalyzed, Ortho-Selective C-H Halogenation of Benzyl Nitriles, Aryl Weinreb Amides, and Anilides.

Palladium-Catalyzed, Ortho-Selective C-H Halogenation of Benzyl Nitriles, Aryl Weinreb Amides, and Anilides.

General Method for the Preparation of Indole-2-Weinreb Amides

Indole-2-Weinreb amides are obtained via thermolysis of α-azidocinnamic acid Weinreb amides in a Hemetsberger–Knittel-type cyclization. The required vinyl azides are not accessible by Knoevenagel condensation, but are obtained by cerium(IV)-mediated oxidative azidation of the corresponding cinnamic Weinreb amides.

Ligand-Enabled, Palladium-Catalyzed β-C(sp3)-H Arylation of Weinreb Amides.

We report the development of Pd(II)-catalyzed C(sp3)-H arylation of Weinreb amides. This work demonstrates the first example of using Weinreb amide as a directing group for transition metal-catalyzed C(sp3)-H activation. Both the inductive effect and the potential bidentate coordination mode of the Weinreb amides pose a unique challenge for this reaction development. A pyridinesulfonic acid ligand is designed to accommodate the weak, neutral coordinating property of Weinreb amides via preserving the cationic character of Pd center through zwitterionic assembly of Pd/ligand complexes. DFT studies of the C-H cleavage step indicate that the superior reactivity of 3-pyridinesulfonic acid ligand compared to pyridine, Ac-Gly-OH, and ligandless conditions originates from the stabilization of overall substrate-bound Pd species.

Broadly Applicable Ytterbium-Catalyzed Esterification, Hydrolysis, and Amidation of Imides

An efficient, broadly applicable, operationally simple, and divergent process for the transformation of imides into a range of carboxylic acid derivatives under mild conditions is reported. By simply using catalytic amounts of ytterbium(III) triflate as a Lewis acid promoter in the presence of alcohols, water, amines, or N, O-dimethylhydroxylamine, a broad range of imides is smoothly and readily converted to the corresponding esters, carboxylic acids, amides, and Weinreb amides in good yields. This method notably enables an easy cleavage of oxazolidinone-based auxiliaries.

Cinchonamine Squaramide Catalyzed Asymmetric aza‐Michael Reaction: Dihydroisoquinolines and Tetrahydropyridines

AbstractThe first example of a chiral cinchona‐squaramide catalyzed enantioselective intramolecular aza‐Michael addition for the synthesis of dihydroisoquinolines and tetrahydropyridines has been developed. In general, good yields and excellent enantioselctivities were observed. Broad classes of Michael acceptors, such as enones, esters, thioesters, and Weinreb amides, were successful substrates. The possibility of recycling the catalysts has also been demonstrated. An oxidation of combined enamine and keto functionalities on chiral dihydroisoquinolines leads to a single diastereomer of an architecturally unprecedented tetracyclic core without loss in enantioselectivity.

Cinchonamine Squaramide Catalyzed Asymmetric aza-Michael Reaction: Dihydroisoquinolines and Tetrahydropyridines.

The first example of a chiral cinchona-squaramide catalyzed enantioselective intramolecular aza-Michael addition for the synthesis of dihydroisoquinolines and tetrahydropyridines has been developed. In general, good yields and excellent enantioselctivities were observed. Broad classes of Michael acceptors, such as enones, esters, thioesters, and Weinreb amides, were successful substrates. The possibility of recycling the catalysts has also been demonstrated. An oxidation of combined enamine and keto functionalities on chiral dihydroisoquinolines leads to a single diastereomer of an architecturally unprecedented tetracyclic core without loss in enantioselectivity.

Weinreb Amide Directed Versatile C-H Bond Functionalization under (η5 -Pentamethylcyclopentadienyl)cobalt(III) Catalysis.

The (η5 -pentamethylcyclopentadienyl)cobalt(III) (Cp*CoIII )-catalyzed C-H bond functionalization of aromatic, heteroaromatic, and α,β-unsaturated Weinreb amides was explored. C-H allylation reactions with the use of allyl carbonate and a perfluoroalkene, oxidative alkenylation reactions with the use of ethyl acrylate, iodination reactions with the use of N-iodosuccinimide, and amidation reactions with the use of dioxazolones were catalyzed by Cp*Co(CO)I2 in the presence of a cationic Ag salt and AgOAc to afford various synthetically useful building blocks. Mechanistic studies of the C-H allylation disclosed that the C-H activation step was rate determining and virtually irreversible.

Asymmetric Total Synthesis and Biological Evaluation of Proapoptotic Natural Myrcene‐Derived Cyclohexenyl Chalcones

Based on a bioinspired asymmetric Diels–Alder cycloaddition using a chiral Evans oxazolidinone, the first total synthesis of both enantiomers of two myrcene‐derived cyclohexenyl chalcones, fislatifolione and fislatifolic acid, has been carried out. This strategy was also applied to the total synthesis of nicolaiodesin C. These natural products, as well as their synthetic intermediates, were evaluated by in‐vitro affinity displacement assays, based on the modulation of Bcl‐xL/Bak, Mcl‐1/Bid, and Bcl‐2‐Bim interactions. This study showed that (+)‐fislatifolic acid acts as a dual Bcl‐xL/Mcl‐1 inhibitor with micromolar activity, and that a Weinreb amide intermediate acts as an excellent Mcl‐1/Bcl‐2 dual inhibitor at the submicromolar level.

Substituted α‐Sulfur Methyl Carbanions: Effective Homologating Agents for the Chemoselective Preparation of β‐Oxo Thioethers from Weinreb Amides

The proper generation of α‐thiomethyllithium reagents via reductive lithiation or deprotonation followed by reaction with variously functionalized Weinreb amides represents an excellent method to access β‐oxo thioethers. The procedure is adaptable to alkyl‐ or aryl‐ thiomethyllithium conjugates. It has the advantages of conceptual simplicity and versatility of the addition of organometallics to Weinreb amides with the possibility to fully preserve the optical information contained in the starting materials.

Expeditious and Chemoselective Synthesis of α-Aryl and α-Alkyl Selenomethylketones via Homologation Chemistry.

Diselenoacetals, previously considered byproducts in homologation tactics en route to α-selenoketones, are herein found to be excellent starting materials for this purpose. The easy selenium/lithium exchange they undergo affords seleno carbanions which are smoothly added to Weinreb amides to chemoselectively prepare α-aryl- and α-alkyl seleno methylketones through a single chemical operation. No racemization events are observed in the presence of optically pure starting materials.

Merging lithium carbenoid homologation and enzymatic reduction: A combinative approach to the HIV-protease inhibitor Nelfinavir

An effective stereocontrolled synthesis of the HIV protease inhibitor Nelfinavir is reported. Two transformations were identified crucial for achieving success: the formation of a densely functionalized α-chloroketone via the homologation of a Weinreb amide with chloromethyllithium (LiCH2Cl), followed by its erythro selective reduction into the corresponding chiral chlorohydrin. A commercially available enzyme P2-C02 was particularly well suited for this purpose, affording the key alcohol (in an excellent 99% de), which was then smoothly converted into the active biologically active agent.

Total synthesis of janadolide

The first total synthesis of janadolide, a new cyclic polyketide-peptide hybrid possessing a tert-butyl group, is described. The synthesis of an unsaturated hydroxycarboxylic acid was effected via the lithiation of vinyl iodide followed by addition to a Weinreb amide with a tert-butyl group and stereoselective 1,2-reduction. The cyclic structure was constructed by macrolactamization at the amide bond between the proline moiety and fatty acid moiety.

The dual reactivity of Weinreb amides applied to the late-stage divergent functionalisation of meso pyrrolidines

The dual reactivity of Weinreb amides was exploited to prepare diversified symmetrical and dissymmetrical 2,5-disubstituted pyrrolidines from simple building blocks.

Chemoselective Formation and Reaction of Densely Functionalised Bicyclic Tetramic Acids and Their Biological Activity

Weinreb amide derivatives of tetramates may be effectively accessed by chemoselective Dieckmann reaction, and further react with Grignards in a fully chemoselective reaction, giving rise to unsaturated acyl derivatives not easily available by other routes. These systems are strong chelators of calcium, and some show potent activity against Gram positive bacteria, and one is a first-in-class proteasome inhibitor.

Ionic liquids, microwave irradiation, and the synthesis of aryl Weinreb amides

The Heck coupling of aryl halides and N-methoxy-N-methylacrylamide was investigated in the room-temperature ionic liquids [BMIM][PF6], [BMIM][Br], [BMIM][BF4], [BMIM][OH], [BMIM][HCOO], EAN, PAN, and ETAN. Excellent yields of the expected N-methoxy-N-methylcinnamamides (ca 90%) and purity (> 96%) were afforded on simple diethyl ether extraction from [BMIM][PF6] and [BMIM][OH]. The described procedure was highly substrate tolerant with methyl, methoxy, fluoro, trifluoromethyl, ester, cyano, hydroxy, naphthyl, and quinolone moieties well tolerated. Poor yields or no reactions were observed with –NH2 and –NO2 moieties. The use of microwave irradiation reduced reaction times from 3 h (thermal) to 5–15 min with no substantive effect on reaction outcome.