4-dimethylaminopyridine Research Articles

Synthesis of linear and crosslinked isosorbide-containing poly(β-thioether ester) via amine-catalyzed thiol-Michael addition

In this work, the amine-catalyzed thiol-Michael reaction of isosorbide or isomannide-derived dithiols as Michael-donors, with some diacrylates and dimethacrylates as Michael-acceptors, is reported. In a first part, different amines (1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU), dimethylaminopyridine (DMAP), Amberlyst® A-21 and hexylamine (HA)) were tested as catalysts for reactions involving diacrylates and dimethacrylates in acetonitrile, respectively. Molecular weight taken as the relevant criterion, DBU and DMAP were found to be equally efficient for polymerization with acrylates while DBU was the most efficient one with methacrylates. A library of polymers differing from the structure of the used diacrylate (some of them derived from isosorbide or isomannide) or dimethacrylate was prepared, with fair molecular weights and Tg varying from –22 to +32 °C. Then oligomers with controlled molecular weight and good end group fidelity were prepared, and were further used in a two-stage crosslinking reaction to prepare soft and elastic biobased crosslinked polymers via thiol-Michael addition.

RP-HPLC method development and validation for novel synthesized polyethylene glycol conjugated isotretinoin prodrug

Orally administered Isotretinoin is a highly effective medication for treating cystic acne. The current study is to synthesize Isotretinoin prodrug via an ester linkage to polyethylene glycol (PEG) 4000, with DCC (dicyclohexyl carbodimide) as a coupling agent and DMAP (dimethylamino pyridine) as a catalyst. FT-IR, DSC and 1H NMR were used to characterize the synthesied prodrug. RP-HPLC method was developed and validated for prodrug. Thermo C18 (Hypersil BDS) column (250 mm × 4.6 mm, 5μm) was used for chromatographic separation with acetonitrile: water (95:05% v/v) as a mobile phase. UV detection was done at 344 nm; flow rate was 1mLmin-1 and an column temperature of 35oC. Total runtime of the analytical run was 15 min. High selectivity and good precision features were found in the method validation results, which were examined at six concentration levels. In intra- and inter-assay precision experiment, the RSD was less than 2.0%. The recovery of isotretinoin, which was examined at three different degrees of fortification, ranged from 99.06% to 100.42% and linearity was found for a range of 0. 2 to 100 μg mL-1. The calibration curve was linear over the 0.5-100 μg mL-1 concentration range. Photolytic stability of prodrug was performed under UV light. There was successfully improves the photolytic stability of Isotretinoin prodrug as compare to Isotretinoin.

Copolymerization of β-Butyrolactones into Functionalized Polyhydroxyalkanoates Using Aluminum Catalysts: Influence of the Initiator in the Ring-Opening Polymerization Mechanism.

Within bioplastics, natural poly(3-hydroxybutyrate) (PHB) stands out as fully biocompatible and biodegradable, even in marine environments; however, its high isotacticity and crystallinity limits its mechanical properties and hence its applications. PHB can also be synthesized with different tacticities via a catalytic ring-opening polymerization (ROP) of rac-β-butyrolactone (BBL), paving the way to PHB with better thermomechanical and processability properties. In this work, the catalyst family is extended based on aluminum phenoxy-imine methyl catalyst [AlMeL2], that reveals efficient in the ROP of BBL, to the halogeno analogous complex [AlClL2]. As well, the impact on the ROP mechanism of different initiators is further explored with a particular focus in dimethylaminopyridine (DMAP), a hardly studied initiator for the ROP of BBL. A thorough mechanistic study is performed that evidences the presence of two concomitant DMAP-mediated mechanisms, that lead to either a DMAP or a crotonate end-capping group. Besides, in order to increase the possibilities of PHB post-polymerization functionalization, the introduction of a side-chain functionality is explored, establishing the copolymerization of BBL with β-allyloxymethylene propiolactone (BPLOAll), resulting in well-defined P(BBL-co-BPLOAll) copolymers.

New Polyether Macrocycles as Promising Antitumor Agents-Targeted Synthesis and Induction of Mitochondrial Apoptosis.

A series of previously unknown aromatic polyether macrodiolides containing a cis,cis-1,5-diene moiety in the molecule were synthesized in 47-74% yields. Macrocycle compounds were first obtained by intermolecular esterification of aromatic polyether diols with α,ω-alka-nZ,(n+4)Z-dienedioic acids mediated by N-(3-(dimethylamino)propyl)-N'-ethylcarbodiimide hydrochloride (EDC·HCl) and 4-(dimethylamino)pyridine (DMAP). For the synthesized compounds, studies of cytotoxicity on tumor (Jurkat, K562, U937), conditionally normal (HEK293) cell lines, and normal fibroblasts were carried out. CC50 was determined, and the therapeutic selectivity index of cytotoxic action (SI) in comparison with normal fibroblasts was evaluated. With the involvement of modern methods of flow cytometry for the most promising macrocycles, their effect on mitochondria and the cell cycle was investigated. It was found that a new macrocycle exhibits pronounced apoptosis-inducing activity toward Jurkat cells and can retard cell division by blocking at the G1/S checkpoint. Also, it was shown that the synthesized macrodiolides influence mitochondria due to their high ability to penetrate the mitochondrial membrane.

Preparation of strong, UV-blocking and sustainable glucose-cross-linked cellulose plastics via hydroxyl-yne click reaction

The construction of functional cellulose plastics possessing strong UV-blocking, hydrophilicity, and biodegradability is challenging. Therefore, we provide a novel strategy to successfully prepare sustainable and hydrophilic glucose-cross-linked cellulose (GC) plastics showing effective UV-blocking and excellent mechanical properties via hydroxyl-yne click reaction at room temperature. The results demonstrated that hydroxyl-yne click chemistry enabled efficient crosslinking of cellulose with glucose using 4-dimethylamino pyridine (DMAP) as a catalyst. Moreover, the DMAP residue imparted good UV-shielding properties to GC films exhibiting nearly 100 % UVC (200–275 nm) and 100 % UVB (320–275 nm) shielding ratios. The introduction of glucose imparted superior hydrophilicity (water contact angle of 40.3–43.2°) and improved water adsorption. Additionally, the mechanical properties of the GC films increased with the increasing crosslinking density, and the highest tensile stress was 94 MPa. The water-induced breaking and hydrogen bond reforming strategy led to a stress of 127 MPa and a strain of 25.6 % for the final GC2 film, which were excellent compared to those of the most reported cellulose films. Additionally, GC films were biosafe, exhibited improved oxygen barrier, and good biodegradability. Hence, this study provides a promising and efficient approach for preparing high-performance cellulose plastics.

Synthesis and Characterization of New Nanohybrids Based on Carboxymethyl Scleroglucan and Silica Nanoparticles.

In this study, two new nanohybrids (NH-A and NH-B) were synthesized through carbodiimide-assisted coupling. The reaction was performed between carboxymethyl-scleroglucans (CMS-A and CMS-B) with different degrees of substitution and commercial amino-functionalized silica nanoparticles using 4-(dimethylamino)-pyridine (DMAP) and N,N'-dicyclohexylcarbodiimide (DCC) as catalysts. The morphology and properties of the nanohybrids were investigated by using transmission (TEM) and scanning electron microscopy (SEM), electron-dispersive scanning (EDS), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FT-IR), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-OES), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic light scattering (DLS). The nanohybrids exhibited differences in structure due to the incorporation of polyhedral oligomeric silsesquioxane (POSS) materials. The results reveal that hybrid nanomaterials exhibit similar thermal properties but differ in morphology, chemical structure, and crystallinity properties. Finally, a viscosity study was performed on the newly obtained nanohybrid materials; viscosities of nanohybrids increased significantly in comparison to the carboxymethyl-scleroglucans, with a viscosity difference of 7.2% for NH-A and up to 32.6% for NH-B.

Stereoselective Ring-opening Polymerization of S-Carboxyanhydrides Using Salen Aluminum Catalysts: A Route to High-Isotactic Functionalized Polythioesters.

Polythioesters are important sustainable polymers with broad applications. The ring-opening polymerization (ROP) of S-Carboxyanhydrides (SCAs) can afford polythioesters with functional groups that are typically difficult to prepare by ROP of thiolactones. Typical methods involving organocatalysts, like dimethylaminopyridine (DMAP) and triethylamine (Et3 N), have been plagued by uncontrolled polymerization, including epimerization for most SCAs resulting in the loss of isotacticity. Here, we report the use of salen aluminum catalysts for the selective ROP of various SCAs without epimerization, affording functionalized polythioester with high molecular weight up to 37.6 kDa and the highest Pm value up to 0.99. Notably, the ROP of TlaSCA (SCA prepared from thiolactic acid) generates the first example of a isotactic crystalline poly(thiolactic acid), which exhibited a distinct Tm value of 152.6 °C. Effective ligand tailoring governs the binding affinity between the sulfide chain-end and the metal center, thereby maintaining the activity of organometallic catalysts and reducing the occurrence of epimerization reactions.

Stereoselective Ring‐opening Polymerization of S‐Carboxyanhydrides Using Salen Aluminum Catalysts: A Route to High‐Isotactic Functionalized Polythioesters

AbstractPolythioesters are important sustainable polymers with broad applications. The ring‐opening polymerization (ROP) of S‐Carboxyanhydrides (SCAs) can afford polythioesters with functional groups that are typically difficult to prepare by ROP of thiolactones. Typical methods involving organocatalysts, like dimethylaminopyridine (DMAP) and triethylamine (Et3N), have been plagued by uncontrolled polymerization, including epimerization for most SCAs resulting in the loss of isotacticity. Here, we report the use of salen aluminum catalysts for the selective ROP of various SCAs without epimerization, affording functionalized polythioester with high molecular weight up to 37.6 kDa and the highest Pm value up to 0.99. Notably, the ROP of TlaSCA (SCA prepared from thiolactic acid) generates the first example of a isotactic crystalline poly(thiolactic acid), which exhibited a distinct Tm value of 152.6 °C. Effective ligand tailoring governs the binding affinity between the sulfide chain‐end and the metal center, thereby maintaining the activity of organometallic catalysts and reducing the occurrence of epimerization reactions.

Steglich esterification: A versatile synthetic approach toward the synthesis of natural products, their analogues/derivatives

The exploitation of natural products and their analogues in the field of pharmacology has been regarded as of great importance. It can be attributed to the fact that these scaffolds exhibit diverse chemical properties, distinct biological activities and zenith specificity in their biochemical processes, enabling them to act as favorable structures for lead compounds. The synthesis of natural products has been a crafty and hard-to-achieve task. Steglich esterification reaction has played a significant role in that area. It is a mild and efficient technique for constructing ester linkages. This technique involves the establishment of ester moiety via a carbodiimide-based condensation of a carboxylic acid with an alcohol, thiol or an amine catalyzed by dimethyl aminopyridine (DMAP). Specifically, labile reagents with multiple reactive sites are esterified efficiently with the classical and modified Steglich esterification conditions, which accounts for their synthetic utility. This review encloses the performance of the Steglich esterification reaction in forging the ester linkage for executing the total synthesis of natural products and their derivatives since 2018.

Modulation of carrier conduction in CsPbBr3 perovskite quantum dots with band-aligned electron and hole acceptors.

The lead halide perovskites have emerged as promising materials with intriguing photo-physical properties and have immense potential for photovoltaic applications. A comprehensive study on the kinetics of charge carrier (electron/hole) generation and transfer across the interface is key to realizing their future scope for efficient device engineering. Herein, we investigate the interfacial charge transfer (CT) dynamics in cesium lead halide (CsPbBr3) perovskite quantum dots (PQDs) with energetically favorable electron acceptors, anthraquinone (AQ) and p-benzoquinone (BQ), and hole acceptors such as pyrene and 4-(dimethylamino)pyridine (DMAP). With various steady-state and time-resolved spectroscopic and microscopic measurements, a faster electron transfer rate is estimated for CsPbBr3 PQDs with BQ compared to that of AQ, while a superior hole transfer for DMAP is divulged compared to pyrene. In concurrence with the spectroscopic measurements, conducting atomic force microscopic studies across the electrode-PQD-electrode junction reveals an increment in the conductance of the PQD in the presence of both the electron and hole acceptors. The variation of the density of states calculation in the presence of the hole acceptors offers strong support and validation for faster CT efficiency. The above findings suggest that a careful selection of simple yet efficient molecular arrangements can facilitate rapid carrier transfer, which can be designed as auxiliary layers for smooth CT and help in the engineering of cost-effective photovoltaic devices.

Synthesis and catalytic performance of wood cellulose nanofibers grafted with polylactic acid in rare-earth complexes based on tetrazole carboxylic acids

Stannous octanoate [Sn(Oct)2] and 4-dimethylamino pyridine (DMAP) were used to catalyze the synthesis of amphiphilic cellulose-based graft copolymers, but the acute toxicity of tin ions and DMAP prompts the need for the application of less harmful catalysts. Herein, green catalyst complexes 1–3 [M(H0.5L)2(H2O)5]·2(H2O) (M = Sm, 1; M = Nd, 2; M = Eu, 3; H2L = 4-(3-(tetrazol-5-yl)pyridin-5-yl)benzoic acid) were synthesized, and their properties were systematically investigated. Single-crystal X-ray diffraction showed that the complexes possessed a zero-dimensional structure, while the thermogravimetry and scanning electron microscopy results confirmed their stability after heating at 110 °C for 10 h. Using complexes 1–3 and DMAP as the catalysts, CNFs were grafted with l-lactide via homogeneous ring-opening polymerization to form wood cellulose nanofibers grafted with l-lactide (WGLAs), and the effects of the ratio of wood cellulose nanofibers (WCNFs) to l-lactide ([AGU]/[LA]) and catalyst dosage were studied. The polymerization followed the coordination–insertion mechanism. Under comparable reaction conditions, the grafting ratio of WGLA-1 reached 84.7 %, and the grafting ratio of complex 1 was found to be higher than those achieved using DMAP. WGLAs demonstrated good thermal stability without cytotoxicity, and the residual catalysts in the WGLAs exhibited fluorescence characteristics. Overall, amphiphilic cellulose-based materials with fluorescence emission offered a promising modification strategy to prepare high-performance polymer composites for agriculture and biomedical application.

Reprocessable Non-Isocyanate Polyurethane Vitrimers

Non-isocyanate polyurethanes (NIPUs, polyhydroxyurethanes, PHUs), have emerged as sustainable alternatives to conventional isocyanate-polyol polyurethanes. However, the permanent cross-links in traditional linear, crosslinked polyhydroxyurethane polymer networks hinder their recyclability for high-value applications. In this study, we provide a comprehensive overview of polyhydroxyurethane vitrimers – polymers with intrinsic recyclability – containing dynamic covalent adaptable bonds that allow them to be reprocessed or self-healed under external stimuli such as heat or solvents. These materials exhibit a unique combination of the attributes of thermosets, such as improved heat stability, solvent resistance or enhanced mechanical properties, and the reprocessability of thermoplastics. Various strategies have been explored to enable the reprocessability of PHUs. External catalysts, such as 4-(dimethylamino)pyridine (DMAP) have been used to facilitate exchange reactions and promote reprocessing. Additionally, the use of functionalized silica nanoparticles as reinforcing fillers has influenced the material’s behavior during reprocessing. Another method involved the incorporation of dynamic disulfide bonds to expedite reprocessing times for PHU networks, while dissociative dynamic chemistry has enabled self-healing behavior in certain partially cross-linked NIPUs. These advancements demonstrate the potential for tailoring the reprocessability and mechanical attributes of NIPUs, paving the way for sustainable and versatile polymeric materials, and addressing the environmental concerns associated with traditional polyurethanes.

High-Glass-Transition Polyesters Produced with Phthalic Anhydride and Epoxides by Ring-Opening Copolymerization (ROCOP).

Polyesters with a high glass transition temperature above 130 °C were obtained from limonene oxide (LO) or vinylcyclohexene oxide (VCHO) and phthalic anhydride (PA) in the presence of commercial salen-type complexes with different metals-Cr, Al, and Mn-as catalysts in combination with 4-(dimethylamino) pyridine (DMAP), bis-(triphenylphosphorydine) ammonium chloride (PPNCl), and bis-(triphenylphosphoranylidene)ammonium azide (PPNN3) as cocatalysts via alternating ring-opening copolymerization (ROCOP). The effects of the time of precontact between the catalyst and cocatalyst and the polymerization time on the productivity, molar mass (Mw), and glass transition temperature (Tg) were evaluated. The polyesters were characterized by a molar mass (Mw) of up to 14.0 kg/mol, a narrow dispersity Tg of up to 136 °C, and low (<3 mol%) polyether units. For poly(LO-alt-PA) copolymers, biodegradation tests were performed according to ISO 14851 using the respirometric biochemical oxygen demand method. Moreover, the vinyl double bond present in the poly(LO-alt-PA) copolymer chain was functionalized using three different thiols, methyl-3-mercaptopropionate, isooctyl-3-mercaptopropionate, and butyl-3-mercaptopropionate, via a click chemistry reaction. The thermal properties of poly(LO-alt-PA), poly(VCHO-alt-PA) and thiol-modified poly(LO-alt-PA) copolymers were extensively studied by DSC and TGA. Some preliminary compression molding tests were also conducted.

Osmium ester-hinged chlorin dimers

A bis(dihydroxychlorin) osmate ester is formed as a side product in the osmylation of meso-tetraphenylporphyrin. The product can also be formed in good yield along well-known reaction pathways of osmate esters by treatment of the monomeric chlorin diol osmate ester bispyridine complex with acid. The dimer was spectroscopically characterized. The free base dimer can be metalated with zinc(II). The bis([dihydroxychlorinato]zinc) osmate ester dimer was spectroscopically and structurally characterized, showing its clamshell architecture with a 42[Formula: see text] angle between the mean planes of the two metallochlorin chromophores and a 9.11 Å zinc-to-zinc separation. Upon reaction with dimethylaminopyridine (DMAP), the clamshell structure pivots around the osmium center and arranges the two chromophores, each zinc center coordinated to DMAP, in maximum separation from each other, as shown by structural analysis. Preliminary 1H NMR titration data are presented that show the bis-zinc clamshell structure to form a 1:1 supramolecular complex with diethylenetriamine (DETA), expressing a three-point recognition motive: the terminal amine functionalities coordinate to the zinc ions in each half-shell, thus bridging both chromophores, and the central amine functionality was deduced to be H-bonded to the osmium oxo group pointing toward the inside of the host. The UV-vis spectroscopic response upon DETA binding shows greater complexity in the interaction at higher ligand:host ratios, suggesting multiple binding modes. A similarly complex binding situation is also observed for the interactions of the chlorin osmate ester monomer with DETA.

Salen-like Chromium and Aluminum Complexes as Catalysts in the Copolymerization of Epoxides with Cyclic Anhydrides for the Synthesis of Polyesters.

Chromium and aluminum complexes bearing salalen ligands were explored as catalysts for the ring-opening copolymerization (ROCOP) of succinic (SA), maleic (MA), and phthalic (PA) anhydrides with several epoxides: cyclohexene oxide (CHO), propylene oxide (PO), and limonene oxide (LO). Their behavior was compared with that of traditional salen chromium complexes. A completely alternating enchainment of monomers to provide pure polyesters was achieved with all the catalysts when used in combination with 4-(dimethylamino)pyridine (DMAP) as the cocatalyst. Poly(propylene maleate-block-polyglycolide), a diblock polyester with a precise composition, was obtained by switch catalysis, in which the same catalyst was able to combine the ROCOP of propylene oxide and maleic anhydride with the ring-opening polymerization (ROP) of glycolide (GA) through a one-pot procedure, starting from an initial mixture of the three different monomers.

DMAP Catalyzed One-Pot Curtius Rearrangement Using 1,1-Dimethyl-2,2,2-trichloroethoxycarbonyl Azide.

We report our development of a controllable, base-free, one-pot Curtius rearrangement using 1,1-dimethyl-2,2,2-trichloroethoxycarbonyl azide (DMTN3) with 4-(dimethylamino)pyridine (DMAP) as a catalyst. The scope of this catalytic process covers a range of primary, secondary, and tertiary alkyl and aryl carboxylic acids that allow the efficient stereospecific construction of alkyl or aryl isocyanates. Examples are reported of late-stage decarboxylative isocyanation of natural products and drug molecules, the rapid synthesis of several drugs, and the utilization of in situ generated DMTN3. Detailed studies of the mechanism indicate that the reaction rate depends on the concentration of the DMAP catalyst, and this ensures that the reaction is a mild and controllable process.

Expanding the Utility of β-Diketiminate Ligands in Heavy Group VI Chemistry of Molybdenum and Tungsten.

We report the synthesis of 17 molybdenum and tungsten complexes supported by the ubiquitous BDI ligand framework (BDI = β-diketiminate). The focal entry point is the synthesis of four molybdenum and tungsten(V) BDI complexes of the general formula [MO(BDIR)Cl2] [M = Mo, R = Dipp (1); M = W, R = Dipp (2); M = Mo, R = Mes (3); M = W, R = Mes (4)] synthesized by the reaction between MoOCl3(THF)2 or WOCl3(THF)2 and LiBDIR. Reactivity studies show that the BDIDipp complexes are excellent precursors toward adduct formation, reacting smoothly with dimethylaminopyridine (DMAP) and triethylphosphine oxide (OPEt3). No reaction with small phosphines has been observed, strongly contrasting the chemistry of previously reported rhenium(V) complexes. Additionally, the complexes 1 and 2 are good precursors for salt metathesis reactions. While 1 can be chemically reduced to the first stable example of a Mo(IV) BDI complex 15, reduction of 2 resulted in degradation of the BDI ligand via a nitrene transfer reaction, leading to MAD (4-((2,6-diisopropylphenyl)imino)pent-2-enide) supported tungsten(V) and tungsten(VI) complexes 16 and 17. All reported complexes have been thoroughly studied by VT-NMR and (heteronuclear) NMR spectroscopy, as well as UV-vis and EPR spectroscopy, IR spectroscopy, and X-ray diffraction analysis.

Ten-Membered Cyclodecatetraene Derivatives Including Two Gallium Atoms: Experimental and Theoretical Studies on Synthesis, Structures, and Their Transformations to Nine- and Five-Membered Gallacycles

The chemistry of medium-sized ring compounds, including group 13 elements, has scarcely been investigated. Herein, we report that 5,10-digallacyclodeca-1,3,6,8-tetraene derivatives Cl2Ga2C8R8 (R = Me (5a), Et (5b)) can be obtained by the reaction of GaCl3 and zirconacyclopentadiene Cp2ZrC4R4 (R = Me (2a), Et (2b), Cp: η5-C5H5) in toluene. X-ray crystal structure analysis revealed that compound 5b has a 10-membered cyclodecatetraene structure composed of two butadiene skeletons and two GaCl fragments. X-ray crystal structure analysis and IR measurement confirmed that compound 5b forms Ga2Cl2 four-membered rings via intermolecular Cl to Ga donor–acceptor interactions, which result in the formation of oligomeric chain structures in the solid state and toluene solution. The treatment of compound 5b with 2 equivalents of 4-(dimethylamino)pyridine (DMAP) proceeded via the coordination of DMAP to the Ga center and the ring contraction to give DMAP-coordinated five-membered gallole Cl(DMAP)GaC4Et4 (4bDMAP). The reaction of compound 5a with 2 equivalents of MesLi (Mes: 2,4,6-Me3C6H2) in toluene to form a 9,10-digallabicyclo[4.3.1]decatriene derivative (MesGaC8Me8)GaMes (6a) caused ring contraction. Theoretical investigation revealed that the 10-membered ring derivative, Cl2Ga2C8H8 (GaH-10), is formed by the dimerization of two gallole molecules, ClGaC4H4 (GaH-5), via the addition of two Ga–C bonds without an energy barrier. The immediate formation of GaH-10 was attributed to the transannular electronic interaction between the expanded empty p-orbital on the Ga atom and the electron-rich sp2 carbons of the C═C double bond in GaH-5. Moreover, GaH-10 and one of the isomer, nine-membered ring derivative (ClGaC8H8)GaCl, were found to be thermodynamically more stable, as compared to GaH-5.

One-Pot Synthesis of 1,3,4-Oxadiazines from Acylhydrazides and Allenoates.

The framework of 1,3,4-oxadiazine is crucial for numerous bioactive molecules, but only a limited number of synthetic methods have been reported for its production. In 2015, Wang's group developed a 4-(dimethylamino)pyridine (DMAP)-catalyzed [2 + 4] cycloaddition of allenoates with N-acyldiazenes, which provided an atom-efficient route for 1,3,4-oxadiazines. However, the practicality of this method was limited by the instability of N-acyldiazenes as starting materials. Building upon our ongoing research about the aerobic oxidation of hydrazides and their synthetic applications, we hypothesized that aerobic oxidative cycloadditions using acylhydrazides instead of N-acyldiazenes may provide a more practical synthetic route for 1,3,4-oxadiazines. In this manuscript, we describe a one-pot synthetic protocol for 1,3,4-oxadiazines from acylhydrazides and allenoates. The developed one-pot protocol consists of aerobic oxidations of acylhydrazides into N-acyldiazenes using NaNO2 and HNO3, followed by the DMAP-catalyzed cycloaddition of allenoate with the generated N-acyldiazenes. A variety of 1,3,4-oxadiazines were produced in good to high yields. In addition, the practicality of the developed method was demonstrated by a gram-scale synthesis of 1,3,4-oxadiazine.

Ferrocene-Derived Palladium(II)-Based Metallosupramolecular Structures: Synthesis, Guest Interaction, and Stimulus-Responsiveness Studies

Using ferrocene-based ligand systems, a series of heterobimetallic architectures of the general formula [PdmLn]x+ were designed with the aim of installing an opening and closing mechanism that would allow the release and binding of guest molecules. Palladium complex formation was achieved through coordination to pyridyl groups, and using 2-, 3-, and 4-pyridyl derivatives provided access to defined PdL, PdL2, and Pd2L4 structures, respectively. The supramolecular complexes were characterized using nuclear magnetic resonance (NMR) and infrared spectroscopy, mass spectrometry, and elemental analysis, and for some examples density functional theory calculations and single-crystal X-ray diffraction analysis. 1H NMR spectroscopy was used to investigate disassembly and reassembly of the metallosupramolecular structures. The former was induced by cleavage of the relatively labile Pd-Npyridyl bonds with the introduction of the competing ligands N,N'-dimethylaminopyridine (DMAP) and Cl- (using tetrabutylammonium chloride) to yield [Pd(DMAP)4]2+ and [PdCl4]2-, respectively. The process was found to be reversible for several of the heterodimetallic compounds, with the addition of H+ or Ag+ triggering complex reassembly. Guest binding studies with several architectures revealed interactions with the anionic guests p-toluenesulfonate and octyl sulfate, but not with neutral molecules. Furthermore, the release of guests was reversibly induced with Cl- ions as a stimulus.