Reaction of amines with methylene chloride. Evidence for rapid aminal formation from N-methylenepyrrolidinium chloride and pyrrolidine

Functionalization of 2-Mercapto-5-methyl-1,3,4-thiadiazole: 2-(ω-Haloalkylthio) Thiadiazoles vs. Symmetrical Bis-Thiadiazoles

A study on the functionalisation of 2-mercapto-5-methyl-1,3,4-thiadiazole has been conducted, yielding two series of products: 2-(ω-haloalkylthio)thiadiazoles and symmetrical bis-thiadiazoles, with variable chain lengths. The experimental conditions were optimised for each class of compounds by altering the base used and the reagents' proportions, leading to the development of separate protocols tailored to their specific reactivity and purification needs. The target halogenide reagents and bis-thiadiazole ligands were obtained either as single products or as mixtures easily separable by chromatography. Characterisation of the products was performed using 1D and 2D NMR spectra in solution, complemented by single crystal X-ray diffraction (XRD) for selected samples, to elucidate their structural properties.

Unexpected Reaction Products of Uracil and Its Methyl Derivatives with Acetic Anhydride and Methylene Chloride

New acetyl derivatives of uracil, 6-methyluracil, and thymine were obtained in the course of an unconventional synthesis in methylene chloride. It was shown that products with the acetyloxymethyl fragment are formed according to a mechanism different from that for products with the acetyloxyethyl group. In particular, for uracil it was proven that the reaction with Ac₂O, TEA, and CH₂Cl₂ leads to 1-acetyloxymethyluracil, where the N¹ substituent is composed of the -CH₂- fragment that originated from CH₂Cl₂ and the 1-acetyloxy moiety from Ac₂O. The reaction of uracil with Ac₂O, TEA, CH₂Cl₂, and DMAP leads to an acetyloxyethyl derivative in which the -CH₂-CH₂- fragment originates from TEA and the 1-acetyloxy moiety from Ac₂O. A possible mechanism for the formation of new compounds was suggested and supported by the density functional theory/B3LYP quantum mechanical calculations. New compounds (39 in total, including seven deuterated) were fully characterized by nuclear magnetic resonance and high-resolution mass spectrometry techniques.

From cyclic amines and acetonitrile to amidine zinc(ii) complexes

A seemingly simple combination of [Zn(quin)₂(H₂O)] (quin⁻ = quinaldinate) and a selected secondary cyclic amine, piperidine (pipe), pyrrolidine (pyro) or morpholine (morph), afforded in acetonitrile a number of products: anionic homoleptic quinaldinate, neutral heteroleptic quinaldinate/amine and quinaldinate/amidine complexes. The piperidine and pyrrolidine systems underwent reaction with acetonitrile to give amidines. The in situ formed piperidinoacetamidine (pipeam) or pyrrolidinoacetamidine (pyroam) coordinated to zinc(ii). Reactions with piperidine led to trans-[Zn(quin)₂(pipe)₂]·2CH₃CN (1), [Zn(quin)₂(pipe)]·cis-[Zn(quin)₂(pipe)₂] (2), pipeH[Zn(quin)₃]·CH₃CN (3), [Zn(quin)₂(pipeam)]·CH₃CN (4a), [Zn(quin)₂(pipeam)]·2CHCl₃ (4b), pipeamH[Zn(quin)₃] (5) and pipeamH[Zn(quin)₂(CH₃COO)]·acetamide (6) (pipeH⁺ and pipeamH⁺ denote protonated amine or amidine). By analogy, [Zn(quin)₂(pyro)₂] (7), pyroH[Zn(quin)₃]·CH₃CN (8), pyroH[Zn(quin)₂Cl] (9), [Zn(quin)₂(pyroam)]·CH₃CN·0.5pyroam·0.5H₂O (10a), [Zn(quin)₂(pyroam)]·2CHCl₃ (10b), [Zn(quin)₂(pyroam)]·CH₂Cl₂ (10c) and pyroamH[Zn(quin)₃] (11) were obtained in the pyrrolidine reactions. The morpholine system allowed isolation of only two novel products, trans-[Zn(quin)₂(morph)₂] (12) and morphH[Zn(quin)₃]·CH₃CN (13). Importantly, no amidine could be isolated. Instead, in autoclaves at 105 °C morpholine degraded to ammonia, as confirmed by mass spectrometry of the gas phase. pyroamH[Zn(quin)₃] exists in two polymorphs which differ in the binding modes of quinaldinate ligands. In 11triclinic, the metal ion of [Zn(quin)₃]⁻ features a five-coordinate environment, whereas that in 11monoclinic is surrounded by six donors. Stabilities of the [Zn(quin)₃]⁻ isomers were assessed with DFT calculations. The one with a six-coordinate zinc(ii) ion was found to be more stable than its five-coordinate counterpart. Favorable intermolecular interactions in the solid state stabilize both and reduce the energy difference between them. The calculations show the conversion of the five-coordinate [Zn(quin)₃]⁻ into its coordinatively saturated isomer to be an almost barrierless process.

Piperidine and pyrrolidine, both belonging to a group of secondary cyclic amines, reacted with acetonitrile in the presence of zinc(ii) to give the corresponding amidines that coordinated to the metal through their imine nitrogen.

Beyond the Simple Copper(II) Coordination Chemistry with Quinaldinate and Secondary Amines

Copper(II) acetate has reacted in methanol with quinaldinic acid (quinoline-2-carboxylic acid) to form [Cu(quin)₂(CH₃OH)]∙CH₃OH (1) (quin⁻ = an anionic form of the acid) with quinaldinates bound in a bidentate chelating manner. In the air, complex 1 gives off methanol and binds water. The conversion was monitored by IR spectroscopy. The aqua complex has shown a facile substitution chemistry with alicyclic secondary amines, pyrrolidine (pyro), and morpholine (morph). trans-[Cu(quin)₂(pyro)₂] (2) and trans-[Cu(quin)₂(morph)₂] (4) were obtained in good yields. The morpholine system has produced a by-product, trans-[Cu(en)₂(H₂O)₂](morphCOO)₂ (5) (morphCOO⁻ = morphylcarbamate), a result of the copper(II) quinaldinate reaction with ethylenediamine (en), an inherent impurity in morpholine, and the amine reaction with carbon dioxide. (pyroH)[Cu(quin)₂Cl] (3) forms on the recrystallization of [Cu(quin)₂(pyro)₂] from dichloromethane, confirming a reaction between amine and the solvent. Similarly, a homologous amine, piperidine (pipe), and dichloromethane produced (pipeH)[Cu(quin)₂Cl] (11). The piperidine system has afforded both mono- and bis-amine complexes, [Cu(quin)₂(pipe)] (6) and trans-[Cu(quin)₂(pipe)₂] (7). The latter also exists in solvated forms, [Cu(quin)₂(pipe)₂]∙CH₃CN (8) and [Cu(quin)₂(pipe)₂]∙CH₃CH₂CN (9). Interestingly, only the piperidine system has experienced a reduction of copper(II). The involvement of amine in the reduction was undoubtedly confirmed by identification of a polycyclic piperidine compound 10, 6,13-di(piperidin-1-yl)dodecahydro-2H,6H-7,14-methanodipyrido[1,2-a:1′,2′-e][1,5]diazocine.

An Efficient Approach to Aromatic Aminomethylation Using Dichloromethane as Methylene Source

Ultrasound-promoted N-aminomethylation of indoles can be achieved in basic medium using sodium hydride and dichloromethane (DCM) as C1 donor source. This innovative amino methylation protocol results in good to excellent yields of multifunctional indole derivatives. The procedure is also applicable to other aza-heterocyclic compounds and, interestingly, affords direct access to aminomethyl-substituted aryl alcohols.

Reaction of N,N-Dimethyltryptamine with Dichloromethane Under Common Experimental Conditions

A large number of clinically used drugs and experimental pharmaceuticals possess the N,N-dimethyltryptamine (DMT) structural core. Previous reports have described the reaction of this motif with dichloromethane (DCM), a common laboratory solvent used during extraction and purification, leading to the formation of an undesired quaternary ammonium salt byproduct. However, the kinetics of this reaction under various conditions have not been thoroughly described. Here, we report a series of experiments designed to simulate the exposure of DMT to DCM that would take place during extraction from plant material, biphasic aqueous work-up, or column chromatography purification. We find that the quaternary ammonium salt byproduct forms at an exceedingly slow rate, only accumulates to a significant extent upon prolonged exposure of DMT to DCM, and is readily extracted into water. Our results suggest that DMT can be exposed to DCM under conditions where contact times are limited (<30 min) with minimal risk of degradation and that this byproduct is not observed following aqueous extraction. However, alternative solvents should be considered when the experimental conditions require longer contact times. Our work has important implications for preparing a wide-range of pharmaceuticals bearing the DMT structural motif in high yields and purities.

Synthesis of novel 1,2,4-thiadiazinane 1,1-dioxides via three component SuFEx type reaction

Herein, we report the preparation of 1,2,4-thiadiazinane 1,1-dioxides from reaction of β-aminoethane sulfonamides with dichloromethane, dibromomethane and formaldehyde as methylene donors.

Identification of fused bicyclic derivatives of pyrrolidine and imidazolidinone as dengue virus-2 NS2B-NS3 protease inhibitors

A series of fused ring derivatives of pyrrolidine and imidazolidinone were designed, synthesized, characterized and assayed against the DENV-2 NS2B-NS3 protease and wild-type DENV-2 virus. The linear dipeptide compound 1 and the non-peptidic fused ring compound 2 show comparable activities against DENV-2 NS2B-NS3 protease and wild-type DENV-2 virus in a viral replication assay. The preliminary SAR reveals that a substituent and its stereochemistry at C-3 position, substitution (X) at N-2 arene and a linker (Y) between C-3 position and its attached arene are important for the fused-ring scaffold of pyrrolidino [1,2-c]imidazolidinone to block the active site of NS2B-NS3 protease. This promising structural core will facilitate the discovery of non-peptidic, potent NS2B-NS3 protease inhibitors to stop dengue virus infections.

Peptide synthesis beyond DMF: THF and ACN as excellent and friendlier alternatives

To date, DMF has been considered as the only solvent suitable for peptide synthesis.

Synthesis of 2-vinylbenzofurans via the copper-catalyzed multicomponent reactions involving an oxa-Michael/arylation/vinylation cascade

2-Vinylbenzofurans have been synthesized via the copper-catalyzed one-pot, three-component reactions of o-iodophenols, in situ generated allenes, and dichloromethane. Cascade transformation of oxa-Michael addition, C-arylation, and sp(3)C-H/sp(3)C-Cl conversion-based vinylation has been involved in realizing the construction of this 2-vinylbenzofuran framework.

Direct, Enantioselective Synthesis of Pyrroloindolines and Indolines From Simple Indole Derivatives

The (R)-BINOL•SnCl₄-catalyzed formal (3 + 2) cycloaddition between 3-substituted indoles and benzyl 2-trifluoroacetamidoacrylate is a direct, enantioselective method to prepare pyrroloindolines from simple starting materials. However, under the originally disclosed conditions, the pyrroloindolines are formed as mixtures of diastereomers, typically in the range of 3:1 to 5:1 favoring the exo-product. The poor diastereoselectivity detracts from the synthetic utility of the reaction. We report here that use of methyl 2-trifluoroacetamidoacrylate in conjunction with (R)-3,3'-dichloro-BINOL•SnCl₄ provides the corresponding pyrroloindolines with improved diastereoselectivity (typically ≥10:1). Guided by mechanistic studies, a one-flask synthesis of enantioenriched indolines by in situ reduction of a persistent iminium ion is also described.

On the Synthesis of 1,4,7-Tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane

1,4,7-Tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane is widely used as an intermediate in the preparation of medically important DO3A and DOTA metal chelators. Despite its commercial availability and importance, the literature describing the preparation and properties of the free base is limited and sometimes unclear. We present herein an efficient synthesis of the hydrobromide salt of 1,4,7-tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane, characterize this compound spectroscopically and by X-ray crystallographic analysis, describe its simple conversion to the corresponding free base, characterize this compound spectroscopically and by X-ray crystallographic analysis, and make observations on the reactivity of this interesting and useful compound.

Toward a Better Understanding on the Mechanism of Ortholithiation. Tuning of Selectivities in the Metalation ofmeta-Anisic Acid by an Appropriate Choice of Base

[reaction: see text] If employed in THF at 0 degrees C, LTMP metalates meta-anisic acid at the doubly activated position. In contrast, n-BuLi/t-BuOK deprotonates position C-4 preferentially at low temperature. Functionalization at C-6 requires protection of the C-2 site beforehand. As a result of these findings, a new mechanism is proposed for the heteroatom-directed ortholithiation of aromatic compounds.

Stereoselective synthesis of an anti-HIV drug candidate

The asymmetric synthesis of a Merck anti-HIV drug candidate is described. The target molecule contains four stereogenic centers, three of which are located in a highly functionalized cyclopentane unit. The convergent synthesis involves the preparation of two key advanced intermediates: the cyclopentane unit and a substituted pyrazole unit. The cyclopentane unit was prepared via two different procedures; a highly diastereoselective Diels-Alder reaction with a chiral oxazolidinone auxiliary and a sequence that incorporated a molybdenum-catalyzed asymmetric allylic alkylation reaction to set the stereocenters. The other key step was a highly diastereoselective hydroxyl-directed reductive amination. The overall yield for the 16-step synthesis was 10%.