Primary Alkylamines Research Articles

Copper‐Catalyzed Tandem Cyclization of 2‐(Alkynylaryl)Acetonitriles and Amines: Access to 3‐Hydroxyisoindolinones

AbstractHerein, we describe an approach to the synthesis of 3‐hydroxyisoindolinone derivatives via copper‐catalyzed tandem cyclization of 2‐(alkynylaryl)acetonitriles and amines. This reaction is compatible with 2‐(alkynylaryl)acetonitriles and primary alkyl amines containing various functional groups, providing the corresponding 3‐hydroxyindolinone derivatives with yields ranging from 44%–82%. Preliminary mechanistic studies suggest that the reaction involves oxidation of the benzylic carbon, amide formation, hydration of the alkyne and intramolecular cyclization to produce various 3‐hydroxyisoindolinones. The practicality of the strategy was further demonstrated by gram‐scale synthesis, late‐stage functionalizations, and the post modification of natural products.

Catalyst Free Synthesis of 4‐Aryl/Alkylamino‐1,2‐Naphthoquinones: Applications in Fluorescence Microscopy

AbstractAn efficient one‐step reagent‐free synthesis of 4‐Aryl/alkylamino‐1,2‐naphthoquinones in water and iPrOH (1 : 1) mixture was carried out at room temperature (RT) using 4‐amino‐3‐hydroxynaphthalene‐1‐sulfonic acid and various primary and secondary aryl and alkyl amines. The reaction did not proceed in the absence of air or oxygen. In all cases, good yields (isolated yield: ≥65 %) were observed. The compounds exhibited fluorescence emission bands (400–470 nm) in the visible region upon excitation at their respective λmax values (330–350 nm). We evaluated in vitro cytotoxicity of some of the derivatives against two human breast cancer cell lines (MCF‐7, and MDA‐MB‐231) using the WST‐1 assay. The naphthoquinone derivatives did not show any cytotoxic effects at concentration levels relevant to cellular fluorescence imaging. The imaging experiments revealed that a few of the derivatives hold the potential to be used as cellular fluorescent imaging probes.

Functionalized Congeners of 2H-Chromene P2Y6 Receptor Antagonists.

The P2Y6 receptor (P2Y6R), a Gq-coupled receptor, is a potential drug discovery target for various inflammatory and degenerative conditions. Antagonists have been shown to attenuate colitis, acute lung injury, etc. In the search for competitive antagonists, we have investigated the SAR of 3-nitro-2-(trifluoromethyl)-2H-chromene derivatives, although high affinity is lacking. We now reveal that long-chain amino-functionalized congeners display greatly enhanced affinity in the antagonism of UDP-induced Ca2+ mobilization in human (h) P2Y6R-transfected 1321N1 astrocytoma cells. A 6-(Boc-amino-n-heptylethynyl) analogue 30 (MRS4940) had an IC50 of 162 nM, which was a 123-fold greater affinity than the corresponding unprotected primary alkylamine, 107-fold greater than the corresponding pivaloyl derivative 30, and 132-fold selective compared to the P2Y14R. However, similar Boc-amino chains attached at the 8-position produced weak µM affinity. Thus, the P2Y6R affinity depended on the chain length, attachment point, and terminal functionality. Off-target activities, at 45 sites, were tested for acylamino derivatives 20, 24, 26, 30, 31, and 37, which showed multiple interactions, particularly at the biogenic amine receptors. The more potent analogues may be suitable for evaluation in inflammation and cancer models, which will be performed in future studies.

Low-cost ionic liquid electrolytes based on low-molecular-weight primary and secondary alkylamine hydrochlorides for rechargeable Al batteries

Rechargeable batteries with Al metal as the negative electrode are promising candidates for post‑lithium-ion batteries. However, the cost of the most commonly used electrolytes, chloroaluminate ionic liquids based on 1-ethyl-3-methylimidazolium chloride (EMICl), is prohibitive. Herein, we report a novel, low-cost chloroaluminate ionic liquid electrolyte based on primary and secondary alkylamine hydrochlorides, namely, ethylamine hydrochloride (EtNH3Cl) and dimethylamine hydrochloride (Me2NH2Cl). The advantages of these alkylamine hydrochlorides over their tertiary amine counterparts (Me3NHCl and Et3NHCl) are their lower cost, odorless nature, and a lower molecular weight that would reduce the battery weight. Although the binary systems of EtNH3Cl–AlCl3 and Me2NH2Cl–AlCl3 are not liquids at room temperature, mixing the two systems results in an ionic liquid at room temperature. The electrodeposition of Al and intercalation of AlCl4− into graphite in this electrolyte system are demonstrated. The alkylammonium cations decompose only at potentials below −0.3 V vs. Al. The performance of Al–graphite batteries incorporating this low-cost electrolyte is comparable to that of batteries using the conventional expensive EMICl-based electrolytes under typical charge-discharge conditions. The low-cost EtNH3Cl–Me2NH2Cl–AlCl3 electrolyte is expected to advance Al batteries toward practical application and commercialization.

Electrochemical deoxygenative amination of stabilized alkyl radicals from activated alcohols

Alkylamine structures represent one of the most functional and widely used in organic synthesis and drug design. However, the general methods for the functionalization of the shielded and deshielded alkyl radicals remain elusive. Here, we report a general deoxygenative amination protocol using alcohol-derived carbazates and nitrobenzene under electrochemical conditions. A range of primary, secondary, and tertiary alkylamines are obtained. This practical procedure can be scaled up through electrochemical continuous flow technique.

Iron(II)-Catalyzed 1,2-Diamination of Styrenes Installing a Terminal NH2 Group Alongside Unprotected Amines.

1,2-Diamination of alkenes represents an attractive way to generate differentiated vicinal diamines, which are prevalent motifs in biologically active compounds and catalysts. However, existing methods are usually limited in scope and produce diamines where one or both nitrogens are protected, adding synthetic steps for deprotection and further N-functionalization to reach a desired target. Furthermore, the range of amino groups that can be introduced at the internal position is fairly limited. Here we describe a 1,2-diamination of styrenes that directly installs a free amino group at the terminal position and a wide variety of unprotected nitrogen nucleophiles (primary or secondary alkyl or aromatic amines, sulfoximines, N-heterocycles, and ammonia surrogate) at the internal position. Two complementary sets of conditions encompass electronically activated and deactivated styrenes with diverse substitution patterns and functional groups. Moreover, this strategy can be extended to the 1,2-aminothiolation of styrenes.

Iron(II)‐Catalyzed 1,2‐Diamination of Styrenes Installing a Terminal NH2 Group Alongside Unprotected Amines

1,2‐Diamination of alkenes represents an attractive way to generate differentiated vicinal diamines, which are prevalent motifs in biologically active compounds and catalysts. However, existing methods are usually limited in scope and produce diamines where one or both nitrogens are protected, adding synthetic steps for deprotection and further N‐functionalization to reach a desired target. Furthermore, the range of amino groups that can be introduced at the internal position is fairly limited. Here we describe a 1,2‐diamination of styrenes that directly installs a free amino group at the terminal position and a wide variety of unprotected nitrogen nucleophiles (primary or secondary alkyl or aromatic amines, sulfoximines, N‐heterocycles, and ammonia surrogate) at the internal position. Two complementary sets of conditions encompass electronically activated and deactivated styrenes with diverse substitution patterns and functional groups. Moreover, this strategy can be extended to the 1,2‐aminothiolation of styrenes.

Microwave-Assisted Synthesis of β-N-Aryl Glycoamphiphiles with Diverse Supramolecular Assemblies and Lectin Accessibility.

Glycoamphiphiles have attracted considerable interest in a broad range of application fields owing to their solution and bulk-state self-assembly abilities. Despite their importance, the straightforward synthesis of glycoamphiphiles consisting of a hydrophilic carbohydrate linked to a hydrophobic aglycone remains one of the major challenges in glycosciences. Here, a rapid, simple, and efficient synthetic access to chemically stable glycoamphiphiles at physiological pH, namely, N-(β-d-glycosyl)-2-alkylbenzamide, is reported. It leverages the nonreductive amination of unprotected carbohydrates with ortho-substituted aniline derivatives which could be readily obtained by reacting commercially available primary alkylamines with isatoic anhydride. This strategy avoids protection and deprotection of sugar hydroxyl groups and the use of reductive agents, which makes it advantageous in terms of atom and step economy. Moreover, in order to circumvent the cons of classical N-aryl glycosylation, we investigate the use of microwave as a heat source that provides fast, clean, and high-yield β-N-arylation of unprotected carbohydrates. Their self-assembly into water led to multiple morphologies of dynamic supramolecular glycoamphiphiles that were characterized to assess their ability to bind to lectins from pathogenic bacteria. Biophysical interactions probed by isothermal titration microcalorimetry revealed micromolar affinities for most of the synthesized glycoamphiphiles.

Asymmetric α-C(sp3)–H Allylic Alkylation of Primary Alkylamines by Merging Iridium and Ketone Catalysis

Asymmetric α-C(sp3)–H Allylic Alkylation of Primary Alkylamines by Merging Iridium and Ketone Catalysis

Thermodynamic property estimations for aqueous primary, secondary, and tertiary alkylamines, benzylamines, and their corresponding aminiums across temperature and pressure are validated by measurements from experiments

On Earth and beyond, organic chemistry often occurs in the presence of water within environments that deviate drastically from ambient conditions (25 °C and 1 bar). Accurately predicting aqueous organic reaction pathways is crucial toward understanding planetary scale processes such as the cycling of elements crucial for life (e.g., carbon and nitrogen). Advanced thermodynamic modeling can be utilized to determine the favorability of various organic reactions based on geologically relevant ranges of temperature and pressure, as well as compositional variables (e.g., pH). However, data that would otherwise allow for a diversity of organic compounds and environmental conditions to be modeled are sparse and rarely tested with experiments, particularly with regard to organic-nitrogen compounds. In this work, we develop a framework to estimate thermodynamic properties at ambient conditions that can then be extrapolated across ranges of temperature and pressure for aqueous primary, secondary, and tertiary amines and aminiums (protonated amines), specifically those structures containing linear alkyl chains and benzyl functional groups. We also performed hydrothermal experiments (250 °C, ∼40 bar) involving reactions of methylamines to test our resulting thermodynamic models, and we compare our models for other alkylamines and benzylamines to previous empirical measurements from the literature. Specifically, we use existing thermodynamic data along with our estimates at ambient conditions in combination with a variety of existing extrapolation methods related to the revised Helgeson-Kirkham-Flowers (HKF) equations of state to generate temperature- and pressure-dependent predictions of acid dissociation constants (i.e., pKa values) that strongly agree with previous empirical measurements. We use similar methods to predict product distributions for reactions involving primary, secondary, and tertiary amines/aminiums, as well as ammonia/ammonium and corresponding alcohols whose collective distributions depend on reversible substitution reactions. Our predictions are in good agreement with our experimental results involving the methylamine reaction system as well as previous experiments involving the benzylamine reaction system, for which we also produced thermodynamic estimates involving benzyl alcohol. The agreement between independent theoretical predictions and experimental measurements suggests that our estimated properties can be applied to modeling amine chemistry in other experimental and natural aqueous systems that range in temperature and pressure, providing new tools for planetary exploration.

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.

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.

General Synthesis of Alkyl Amines via Borrowing Hydrogen and Reductive Amination

AbstractAmines are a very important class of compounds and the selective synthesis of differently substituted primary, secondary and tertiary alkyl amines is challenging. Here we present the synthesis of primary, secondary, and tertiary alkyl amines from ammonia and alcohols, aldehydes, ketones and hydrogen by combining borrowing hydrogen or hydrogen autotransfer and reductive amination with hydrogen. The key is a nanostructured, bimetallic Co/Sc catalyst able to mediate both reactions or concepts efficiently. We observe a broad product scope, a very good functional group tolerance, upscaling is easily accomplished and our catalyst is reusable.

Late-Stage Isotopic Exchange of Primary Amines.

Stable isotopes such as 2H, 13C, and 15N have important applications in chemistry and drug discovery. Late-stage incorporation of uncommon isotopes via isotopic exchange allows for the direct conversion of complex molecules into their valuable isotopologues without requiring a de novo synthesis. While synthetic methods exist for the conversion of hydrogen and carbon atoms into their less abundant isotopes, a corresponding method for accessing 15N-primary amines from their naturally occurring 14N-analogues has not yet been disclosed. We report an approach to access 15N-labeled primary amines via late-stage isotopic exchange using a simple benzophenone imine as the 15N source. By activating α-1 and α-2° amines to Katritzky pyridinium salts and α-3° amines to redox-active imines, we can engage primary alkyl amines in a deaminative amination. The redox-active imines proceed via a radical-polar crossover mechanism, whereas the Katritzky salts are engaged in copper catalysis via an electron donor-acceptor complex. The method is general for a variety of amines, including multiple drug compounds, and results in complete and selective isotopic labeling.

3-Trifluoromethyl Pyrrole Synthesis Based on β-CF3-1,3-Enynamides.

A new metal-free method for the rapid, productive, and scalable preparation of 3-trifluoromethyl pyrroles has been developed. It is based on the electrophilic nature of the double bond of β-CF3-1,3-enynamides due to the electron-withdrawing characteristics of the trifluoromethyl groups and the strong nucleophilic nature of alkyl primary amines. Evidence for the highly regioselective 1,4-hydroamination was observed after the isolation and characterization of the allenamide intermediate.

Additive-Free Copper-Catalyzed Benzylic C(sp3)–H Carbamation: Simple Preparation of Primary Benzylic Amines

AbstractA simple and practical method for the synthesis of primary alkylamines by direct functionalization of hydrocarbons is described. The N-Boc-protected alkylamines are readily prepared from tert-butyl (trimethylsilyl)carbamate and N-fluorobenzenesulfonimide in the presence of a Cu(I) catalyst at low catalyst loadings. Advantageously, this process proceeds free of any additive such as auxiliary bases/acids, requires only one equivalent of the substrate, and does not require ligand synthesis. This operationally simple C–H carbamation method shows high site selectivity and good functional-group tolerance, and uses a commercially available Cu precatalyst and oxidant to furnish N-Boc protected alkylamines in yields of 16–83%. The products can be simply deprotected under mild acidic conditions to generate primary benzylic amines. This practical method was subsequently used for the synthesis of the active pharmaceutical ingredients cinacalcet and sertraline.

Modular, automated synthesis of spirocyclic tetrahydronaphthyridines from primary alkylamines

Spirocyclic tetrahydronaphthyridines (THNs) are valuable scaffolds for drug discovery campaigns, but access to this 3D chemical space is hampered by a lack of modular and scalable synthetic methods. We hereby report an automated, continuous flow synthesis of α-alkylated and spirocyclic 1,2,3,4-tetrahydro-1,8-naphthyridines (“1,8-THNs”), in addition to their regioisomeric 1,6-THN analogues, from abundant primary amine feedstocks. An annulative disconnection approach based on photoredox-catalysed hydroaminoalkylation (HAA) of halogenated vinylpyridines is sequenced in combination with intramolecular SNAr N-arylation. To access the remaining 1,7- and 1,5-THN isomers, a photoredox-catalysed HAA step is telescoped with a palladium-catalysed C–N bond formation. Altogether, this provides a highly modular access to four isomeric THN cores from a common set of unprotected primary amine starting materials, using the same bond disconnections. The simplifying power of the methodology is illustrated by a concise synthesis of the spirocyclic THN core of Pfizer’s MC4R antagonist PF-07258669.

Synthesis and characterization of long‐chain (C20 ~ C48) fatty acid amides (FAAms) from soybean oil and alkyl amines for phase change material applications

AbstractBio‐based organic phase change materials (PCMs) have drawn attention considering their great value in environmental sustainability as a latent heat storage strategy. In this study, bio‐based fatty acid amides (FAAms) were synthesized directly from soybean oil and different amines through a solvent‐free reaction with a non‐toxic catalyst (DABCO). The chemical and thermal properties were confirmed by FT‐IR, NMR, DSC, and TGA measurements. The effects of oil saturation and chain length were investigated. FAAms were successfully synthesized from most of the primary alkyl amines with high purity and yield. Fifteen different FAAms exhibit high latent heat (up to 202 J/g) with a single‐phase transition peak. A general trend of increasing enthalpy of fusion, narrower phase transition temperature range, higher melting temperature, and better thermal stability was found with increasing FAAms chain length. An opposite trend was observed for some long‐chain FAAms (C > 42). Overall, a wide choice of green, organic PCMs with comparable thermal properties to petroleum based PCMs is provided in this work. Those FAAms with high working temperatures (>100°C) could expand the application of organic PCM to different fields such as steam generation, textile, rubber industry, etc.