Alkylamines Research Articles

High-Pressure Promoted Nazarov-like Electrocyclization Enables Access to trans-4,5-Diamino-cyclopent-2-enones Bearing Electron-Poor Anilines.

Unlike secondary alkyl amines and electron-rich anilines, secondary electron-poor anilines are challenging amine sources to explore the chemical space of Lewis acid-catalyzed condensation-based transformations with furfural. In this work, we report the efficient synthesis of trans-4,5-diamino cyclopentenones (DCP) using a high-pressure promoted Nazarov-like electrocyclization of Stenhouse salts arising from the Sc(III)-catalyzed condensation of furfural with secondary electron-poor anilines. The reaction enables access to otherwise difficult-to-access DCP and compatibility with a large scope of alkyl and aryl secondary amines. A 2- to 18-fold increase in yields for electron-poor anilines was highlighted using this approach in the synthesis of a pharmacologically active compound.

Catalysis driven by an amyloid–substrate complex

Amine modification through nucleophilic attack of the amine functionality is a very common chemical transformation. Under biorelevant conditions using acidic-to-neutral pH buffer, however, the nucleophilic reaction of alkyl amines (pKa ≈ 10) is not facile due to the generation of ammonium ions lacking nucleophilicity. Here, we disclose a unique molecular transformation system, catalysis driven by amyloid-substrate complex (CASL), that promotes amine modifications in acidic buffer. Ammonium ions attached to molecules with amyloid-binding capability were activated through deprotonation due to the close proximity to the amyloid catalyst formed by Ac-Asn-Phe-Gly-Ala-Ile-Leu-NH2 (NL6), derived from islet amyloid polypeptide (IAPP). Under the CASL conditions, alkyl amines underwent various modifications, i.e., acylation, arylation, cyclization, and alkylation, in acidic buffer. Crystallographic analysis and chemical modification studies of the amyloid catalysts suggested that the carbonyl oxygen of the Phe-Gly amide bond of NL6 plays a key role in activating the substrate amine by forming a hydrogen bond. Using CASL, selective conversion of substrates possessing equivalently reactive amine functionalities was achieved in catalytic reactions using amyloids. CASL provides a unique method for applying nucleophilic conversion reactions of amines in diverse fields of chemistry and biology.

Halogen Promoted Desulfurative Cleavage of Cyclopropylmethyl Thioethers and Amination of the Formed Cyclopropylcarbinyl Cations

AbstractCyclopropylmethyl sulfides react with N‐fluorosulfonimide (NFSI) or molecular iodine, enabling C−S cleavage to generate cyclopropylcarbinyl cations, which evolve through cyclopropane ring‐opening reactions into homoallyl cations suitable to react with nucleophiles present in the reaction media. This desulfurative cleavage of cyclopropylmethyl thioethers under non‐acidic conditions facilitates homoallylation of N‐based nucleophiles such as alkyl or aryl amines as well as sulfonimides through a one‐pot protocol in one or two steps depending on the nucleophile. The reaction is initiated by a halogen‐sulfur bond that causes C−S bond cleavage. Moreover, the reaction with iodine proceeds through homoallyl iodide intermediates.

Hexafluoroisopropanol Promoted Ring‐Opening‐Cyclization of Donor–Acceptor Cyclopropanes with Primary Amines

AbstractWe reveal here a catalyst‐free, ring‐opening‐cyclization of donor‐acceptor cyclopropanes with primary amines to synthesize functionalized dihydropyrroles. This protocol avoids inert conditions and solvents promoted by hexafluoroisopropanol (HFIP). The reaction is quite general with aryl, alkyl, and alicyclic amines. A good number of cyclopropanes bearing keto groups reacted excellently to produce the desired products. Further, we complemented this method with Meldrum's acid‐derived cyclopropanes for synthesizing γ‐lactams. We have demonstrated the post‐synthetic applications of the products and gram‐scale synthesis to highlight the adaptability of this synthetic protocol.

Palladium(II) NCS‐Pincer Complexes Mediated Regioselective Cross Dehydrogenative Alkenation of 2‐Arylthiophenes

AbstractIn this report, we have synthesized two new NCS pincer ligands by the Schiff base reaction of 3‐((phenylthio)methoxy)benzaldehyde (P) with alkyl amines (tbutylamine (L1) and 1‐adamantylamine (L2)). The palladium pincer complexes (tbutylamine=C1 and 1‐adamantylamine=C2) of these ligands were synthesized by their reaction with PdCl2(CH3CN)2 precursor. The newly synthesized ligands and complexes were characterized using various analytical and spectroscopic techniques such as 1H, 13C{1H} Nuclear Magnetic Resonance (NMR), Ultraviolet–visible (UV‐Visible), Fourier Transform Infrared (FTIR) Spectroscopy, and High‐Resolution Mass Spectrometry (HRMS). The structure of the ligand and its coordination mode with palladium precursor were studied with the help of single‐crystal X‐ray diffraction. The complexes showed distorted square planar geometry around the palladium center. The palladium pincer complexes were used as catalysts for the regioselective cross‐dehydrogenative alkenation of 2‐arylthiophene derivatives. The complex C2, where sterically bulky adamantyl ligand is part of the side arm showed a higher yield of alkenation reaction. Only 2.5 mol% catalyst loading was sufficient to achieve 74–95 % yields of desired products with excellent functional group tolerance under mild reaction conditions. The poisoning experiments (PPh3 and Hg) showed the homogeneous nature of the catalytic process. The plausible mechanism of the reaction was proposed based on the control experiments and time‐dependent HRMS studies.

Photoenzymatic Asymmetric Hydroamination for Chiral Alkyl Amine Synthesis.

Chiral alkyl amines are common structural motifs in pharmaceuticals, natural products, synthetic intermediates, and bioactive molecules. An attractive method to prepare these molecules is the asymmetric radical hydroamination; however, this approach has not been explored with dialkyl amine-derived nitrogen-centered radicals since designing a catalytic system to generate the aminium radical cation, to suppress deleterious side reactions such as α-deprotonation and H atom abstraction, and to facilitate enantioselective hydrogen atom transfer is a formidable task. Herein, we describe the application of photoenzymatic catalysis to generate and harness the aminium radical cation for asymmetric intermolecular hydroamination. In this reaction, the flavin-dependent ene-reductase photocatalytically generates the aminium radical cation from the corresponding hydroxylamine and catalyzes the asymmetric intermolecular hydroamination to furnish the enantioenriched tertiary amine, whereby enantioinduction occurs through enzyme-mediated hydrogen atom transfer. This work highlights the use of photoenzymatic catalysis to generate and control highly reactive radical intermediates for asymmetric synthesis, addressing a long-standing challenge in chemical synthesis.

Synergistic System of Alkyl Polyglucoside and Amine Oxide for Enhanced Oil Recovery

Synergistic System of Alkyl Polyglucoside and Amine Oxide for Enhanced Oil Recovery

Comprehensive computational insights on the conformations, electronic properties and binding mechanism of mescaline: A hallucinogenic molecule

In the series of computational investigations of hallucinogenic compounds particularly in unraveling their conformational aspects, mescaline is taken up in this report after having studied psilocybin and psilocin. Six conformers were identified from the relaxed scan of the dihedral angles of which two were taken up for studying their chemical properties. The two low energy conformers differed by about 0.5 kcal.mol-1 at B3LYP/cc-pVTZ and 1.5 kcal.mol-1 at CCSD/cc-PVDZ levels of theory, respectively and structurally the two conformers differ by the orientation of the alkyl amine group vis-à-vis the benzene ring via the N–H---π interaction. Natural Bond Orbital calculations unveiled the existence of intra-molecular π → π*, n → π* charge transfers, and some hyperconjugative interactions that significantly enhance the stability of mescaline. Reduced Density Gradient calculations unraveled the occurrence of strong intramolecular N–H---π interaction in the most stable conformer of mescaline. The calculated geometrical parameters and predicted structure of the most stable conformer of mescaline agree significantly well with the earlier reported conformers from X-ray studies of mescaline. The computed λmax in the UV–visible spectrum, peak positions in the proton NMR spectrum, and vibrational modes exhibit excellent agreement with the previously reported experimental findings. Moreover, we utilized molecular docking and molecular dynamics simulations to elucidate the binding mode and molecular mechanism of mescaline in comparison to other hallucinogenic molecules. Our findings revealed that mescaline displayed a favorable binding energy and induced essential conformational changes, indicating a potential common mechanism of action shared with psilocybin, another hallucinogenic compound.

Cascade Aryne Aminoarylation for Biaryl Phenol Synthesis.

We describe a transition metal-free approach to hindered 3-amino-2-aryl phenols through a cascade nucleophilic addition / Smiles-Truce rearrangement of a functionalized Kobayashi aryne precursor. Under anionic conditions, secondary alkyl amines add to the aryne intermediate to set up an aryl transfer from a neighboring sulfonate group. The use of a sulfonate, rather than the more typical sulfonamide, enables access to phenolic biaryl products that are important motifs in natural products and pharmaceuticals.

Modeling the alkylation of amines with alkyl bromides: explaining the low selectivity due to multiple alkylation.

Nucleophilic substitution reactions of aliphatic amines with alkyl halides represent a simple and direct mechanism for obtaining higher-order aliphatic amines. However, it is well known that these reactions suffer from low selectivity due to multiple alkylations, which is attributed to the higher reactivity of the newly formed amine. In order to provide a detailed explanation for this kind of system, we have investigated the reactivity of primary and secondary amines with 1-bromopropane and 2-bromopropane. The free energy profile in acetonitrile solution was obtained and a detailed microkinetic analysis was needed to analyze this complex reaction system. We have found that the product of the first alkylation is an ion pair corresponding to the protonated secondary amine and the bromide ion, which can transfer the proton to the reactant primary amine. Then, the newly formed secondary amine can also react, leading to a second alkylation to produce a tertiary protonated amine. Our modeling points out that both the proton transfer equilibria and the similar reactivity of the primary and secondary amines produce reduced selectivity. The proton transfer equilibria also contribute to slowing down the kinetics of the first alkylation. The exploration of the mechanism was done by geometry optimization using the CPCM/X3LYP/ma-def2-SVP method, followed by harmonic frequency calculation at this same level of theory. A composite approach was used to obtain the free energy profile, using the more accurate ωB97X-D3/ma-def2-TZVPP level of theory for electronic energy and the SMD model for the solvation free energy. These calculations were performed with the ORCA 4 program. The detailed microkinetic analysis was done using the Kintecus program.

Multicomponent Synthesis of α-Branched Amines via a Zinc-Mediated Carbonyl Alkylative Amination Reaction.

Methods for the synthesis of α-branched alkylamines are important due to their ubiquity in biologically active molecules. Despite the development of many methods for amine preparation, C(sp3)-rich nitrogen-containing compounds continue to pose challenges for synthesis. While carbonyl reductive amination (CRA) between ketones and alkylamines is the cornerstone method for α-branched alkylamine synthesis, it is sometimes limited by the sterically demanding condensation step between dialkyl ketones and amines and the more restricted availability of ketones compared to aldehydes. We recently reported a "higher-order" variant of this transformation, carbonyl alkylative amination (CAA), which utilized a halogen atom transfer (XAT)-mediated radical mechanism, enabling the streamlined synthesis of complex α-branched alkylamines. Despite the efficacy of this visible-light-driven approach, it displayed scalability issues, and competitive reductive amination was a problem for certain substrate classes, limiting applicability. Here, we report a change in the reaction regime that expands the CAA platform through the realization of an extremely broad zinc-mediated CAA reaction. This new strategy enabled elimination of competitive CRA, simplified purification, and improved reaction scope. Furthermore, this new reaction harnessed carboxylic acid derivatives as alkyl donors and facilitated the synthesis of α-trialkyl tertiary amines, which cannot be accessed via CRA. This Zn-mediated CAA reaction can be carried out at a variety of scales, from a 10 μmol setup in microtiter plates enabling high-throughput experimentation, to the gram-scale synthesis of medicinally-relevant compounds. We believe that this transformation enables robust, efficient, and economical access to α-branched alkylamines and provides a viable alternative to the current benchmark methods.

Double-side 2D/3D heterojunctions for inverted perovskite solar cells.

Defects at the top and bottom interfaces of three-dimensional (3D) perovskite photoabsorbers diminish the performance and operational stability of perovskite solar cells owing to charge recombination, ion migration and electric-field inhomogeneities1-5. Here we demonstrate that long alkyl amine ligands can generate near-phase-pure 2D perovskites at the top and bottom 3D perovskite interfaces and effectively resolve these issues. At the rear-contact side, we find that the alkyl amine ligand strengthens the interactions with the substrate through acid-base reactions with the phosphonic acid group from the organic hole-transporting self-assembled monolayer molecule, thus regulating the 2D perovskite formation. With this, inverted perovskite solar cells with double-side 2D/3D heterojunctions achieved a power conversion efficiency of 25.6% (certified 25.0%), retaining 95% of their initial power conversion efficiency after 1,000 h of 1-sun illumination at 85 °C in air.

Cu-Catalyzed Coupling of Aliphatic Amines with Alkylboronic Esters.

We report a Cu-catalyzed oxidative coupling of aliphatic amines with benzylic and aliphatic boronic esters to give high value alkyl amines, products found widely in applications from medicinal chemistry to materials science. This operationally simple reaction, which can be performed on gram scale, runs under mild conditions and exhibits broad functional group tolerance. The terminal oxidant of the reaction is O2 from the air, avoiding the need for additional chemical oxidants. Investigation into the reaction mechanism suggests that the boronic ester is activated by an aminyl radical, formed through oxidation of the amine by the Cu catalyst, to give a key alkyl radical intermediate. To demonstrate its utility and potential for late-stage functionalization, we showcase the method as the final step in the total synthesis of a TRPV1 antagonist.

Substrate‐induced Selective α‐C(sp3)−H Activation of N‐alkyl Amines: Synthesis of Coumarin‐fused Quinolinones under Air

AbstractA substrate‐induced synthesis of coumarin‐fused quinolinones is achieved from 4‐(phenylamino)‐2H‐chromen‐2‐ones using N‐alkyl amines as the solvent and a carbon source under air conditions without any catalysts in one pot. This protocol highlights the special roles of 4‐(phenylamino)‐2H‐chromen‐2‐ones which were not only used as reactants but also as an internal oxidant selectively activated N‐α‐C(sp3)−H bond. This reaction features catalyst‐free, broad substrate scopes (N‐alkyl amines 27 examples and quinolinones 24 examples), operationally simple for the one‐step synthesis, and recovery and recycling of the solvent.

A Convenient Oligonucleotide Conjugation via Tandem Staudinger Reaction and Amide Bond Formation at the Internucleotidic Phosphate Position.

Staudinger reaction on the solid phase between an electronodeficit organic azide, such as sulfonyl azide, and the phosphite triester formed upon phosphoramidite coupling is a convenient method for the chemical modification of oligonucleotides at the internucleotidic phosphate position. In this work, 4-carboxybenzenesulfonyl azide, either with a free carboxy group or in the form of an activated ester such as pentafluorophenyl, 4-nitrophenyl, or pentafluorobenzyl, was used to introduce a carboxylic acid function to the terminal or internal internucleotidic phosphate of an oligonucleotide via the Staudinger reaction. A subsequent treatment with excess primary alkyl amine followed by the usual work-up, after prior activation with a suitable peptide coupling agent such as a uronium salt/1-hydroxybenzotriazole in the case of a free carboxyl, afforded amide-linked oligonucleotide conjugates in good yields including multiple conjugations of up to the exhaustive modification at each phosphate position for a weakly activated pentafluorobenzyl ester, whereas more strongly activated and, thus, more reactive aryl esters provided only single conjugations at the 5'-end. The conjugates synthesized include those with di- and polyamines that introduce a positively charged side chain to potentially assist the intracellular delivery of the oligonucleotide.

Investigation into a Tetrahydroquinazoline Scaffold

AbstractA new 5,6,7,8‐tetrahydroquinazoline (i. e. 1,3‐diazanaphthalene) scaffold with four points of diversification RA−RD was prepared. The sequence started from nitroalkanes RCCH2NO2 (with RC = Me, Bu), ethyl acrylate and amidines RAC(NH)NH2 (with RA = Ph, 4‐pyridyl) which were converted in a conjugate addition, Dieckmann condensation and pyrimidine ring formation. After transformation of the OH group in 4‐position to a chloro leaving group, residues RB were introduced by nucleophilic substitution with alkyl amines RBNH2 (10 examples) or aryl thiols RBSH (two examples). Finally, the nitro group in the 6‐position was reduced and the primary amino function amidated with various carboxylic acids RDCO2H. Along this seven‐step sequence, eight examples of the fully decorated scaffold were prepared.

Asymmetric α-C(sp3)−H allylic alkylation of primary alkylamines by synergistic Ir/ketone catalysis

Primary alkyl amines are highly reactive in N-nucleophilic reactions with electrophiles. However, their α-C−H bonds are unreactive towards electrophiles due to their extremely low acidity (pKa ~57). Nonetheless, 1,8-diazafluoren-9-one (DFO) can activate primary alkyl amines by increasing the acidity of the α-amino C−H bonds by up to 1044 times. This makes the α-amino C−H bonds acidic enough to be deprotonated under mild conditions. By combining DFO with an iridium catalyst, direct asymmetric α-C−H alkylation of NH2-unprotected primary alkyl amines with allylic carbonates has been achieved. This reaction produces a wide range of chiral homoallylic amines with high enantiopurities. The approach has successfully switched the reactivity between primary alkyl amines and allylic carbonates from intrinsic allylic amination to the α-C−H alkylation, enabling the construction of pharmaceutically significant chiral homoallylic amines from readily available primary alkyl amines in a single step.

Catalytic One‐Pot Reductive Amination of Carboxylic Acids

AbstractThe broad applications of primary alkyl amines in various fields have spurred extensive interests in synthetic organic chemistry. Recently, the reductive amination of carboxylic acids has become an attractive and practical strategy for synthesizing primary alkyl amines, due to their wide availability and bench stability. However, the inherent stability and higher oxidation state of carboxylic acids render this new strategy with new challenges. This Concept provides a summary of the recent advancements in the reductive aminations of carboxylic acids, specifically focusing on the catalytic tactics, underlying mechanisms, and applications in the synthesis of valuable products.

Condensation of Amines with S-Methyl Thiouronium Salts: Another Entry for the Synthesis of Amidines

AbstractWe present a condensation of primary aryl or alkyl amines with S-methyl thiouronium salts to obtain N,N,N′-trisubstituted amidines. High yields, short reaction times, and a fair substrate scope are the noteworthy features of this protocol. Surprisingly, the reaction of a thiouronium salt with 4-aminopyridine gave 1-(4-methoxybenzoyl)piperidine.

Aminocarbonylation Reaction Using a Pd-Sn Heterobimetallic Catalyst: Three-Component Coupling for Direct Access of the Amide Functionality.

A heterobimetallic "Pd-Sn" catalyst, namely, PdCl(PPh3)2SnCl3, efficiently catalyzes the aminocarbonylation reaction of aryl iodides with amines under the atmospheric pressure of CO in the absence of a base and additive. Primary, secondary, and alkyl amines all afforded the corresponding amides in good to excellent yields with high selectivity. A broad range of functional groups were tolerated. The method was further extended to the synthesis of biologically active isoindoline-1,3-diones in the presence of triethylamine. A mechanism is proposed for the reaction.