Intermolecular 1,3-Dipolar Cycloaddition Reaction of N-Carbamoyl Nitrones Generated by N-Selective Carbamoylation of Oximes with Isocyanates.

N-Selective carbamoylation reaction of oximes with isocyanates generates nitrones, which undergo 1,3-dipolar cycloaddition with various dipolarophiles to afford diverse isoxazolidines. Notably, combinations of highly electron-rich oxime and highly electron-deficient dipolarophile exhibited high reactivity, with product yields of up to 94 %. The substituent on the isoxazolidine-nitrogen atom could be successfully removed without loss of the cyclic structure. Computational studies have also elucidated the mechanism of the reaction and origin of stereoselectivity.

Reversible Coupling of Germylone with Isocyanates.

The germylone dimNHCGe (5, dimNHC=diimino N-heterocyclic carbene) undergoes a [2+2] cycloaddition with isocyanates RNCO (R=4-tolyl or 3,5-xylyl) to furnish novel alkyl carboxamido germylenes 7 (R=4-tolyl) and 8 (R=3,5-xylyl), featuring a C-C bond between the former carbene carbon and the isocyanate moiety. Heating a mixture of 8 with 4-tolyl isocyanate to 100 °C results in isocyanate metathesis, demonstrating reversible C-C bond formation on the reduced germanium compound. DFT calculations suggest that this process occurs via the reductive dissociation of isocyanate from 8 that regenerates the parent Ge(0) compound 5.

UV Laser-Induced Photodecomposition of Matrix-Isolated Salicylhydroxamic Acid: Identification of New Isocyanate Complexes.

Photochemical reactions of salicylhydroxamic acid were induced using tunable UV laser radiation followed by FTIR spectroscopy. Four pairs of co-products were experimentally found to appear in the photolysis: C6H4(OH)NCO⋯H2O (1), C6H4(OH)C(O)N⋯H2O (2), C6H4(OH)2⋯HNCO (3), and C6H4(OH)NHOH⋯CO (4). The comparison of the theoretical spectra with the experimental ones allowed us to determine the structures of the complexes formed in the matrices. The mechanisms of the reaction channels leading to the formation of the photoproducts were proposed. It was concluded that the first step in the formation of the complexes (1), (2), and (3) was the scission of the N-O bond, whereas the creation of complex (4) was due to cleavage of the C-N bond.

Non-Isocyanate Urethane Acrylate Derived from Isophorone Diamine: Synthesis, Characterization and Its Application in 3D Printing.

In this paper, urethane-based acrylates (UA) were prepared via an environmentally friendly non-isocyanate route. Isophorone diamine (IPDA) reacted with ethylene carbonate (EC), producing carbamate containing amine and hydroxyl groups, which further reacted with neopentyl glycol diacrylate (NPGDA) by aza Michael addition, forming UA. The structures of the obtained intermediates and UA were characterized by 1H NMR and electrospray ionization high-resolution mass spectrometry (ESI-HRMS). The photopolymerization kinetics of UA were investigated by infrared spectroscopy. The composite with obtained UA can be UV cured quickly to form a transparent film with a tensile strength of 21 MPa and elongation at break of 16%. After UV curing, the mono-functional urethane acrylate was copolymerized into the cross-linked network in the form of side chains. The hydroxyl and carbamate bonds on the side chains have high mobility, which make them easy to form stronger dynamic hydrogen bonds during the tensile process, giving the material a higher tensile strength and elongation at break. Therefore, the hydrogen bonding model of a cross-linked network is proposed. The composite with UA can be 3D printed into models.

Innovative Approach to Chiral Polyurethanes: Asymmetric Copolymerization with Isocyanates.

The introduction of nitrogen-containing functional groups to chiral polymer backbones enables the tailoring of physical properties and offers opportunities for further post-polymerization modification. However, the substrate scope of such polymers is extremely limited because monomers having nitrogen-containing groups can change coordination state with respect to the metal centers, thus decreasing the activity and enantioselectivity and even poisoning the catalyst completely. In this paper, we report our attempts to carry out the asymmetric copolymerization of meso-epoxide with highly reactive isocyanates. In particular, we found that biphenol-linked bimetallic Co(III) complexes with multiple chiral centers are very efficient in catalyzing this asymmetric copolymerization reaction, affording optically active polyurethanes with a completely alternating nature and a high enantioselectivity of up to 94 % ee. Crucially, we identified that the steric hindrance at the phenolate ortho position of the ligand strongly influences the catalytic activity and product enantioselectivity. In addition, density functional theory calculations revealed that the highly sterically bulky substituents change the mechanism from bimetallic to monometallic, and result in the unexpected inversion of the chiral induction direction. Moreover, the high stereoregularity of the produced polyurethanes enhances their thermal stability, and they can be selectively decomposed into oxazolidinones. This study offers a versatile methodology for the synthesis of chiral polymers containing nitrogen functionalities.

Enabling Modular Click Chemistry Library through Sequential Ligations of Carboxylic Acids and Amines.

High-throughput synthesis and screening of chemical libraries play pivotal roles in drug discovery. Click chemistry has emerged as a powerful strategy for constructing highly modular chemical libraries. However, the development of new click reactions and unlocking new click able building blocks remain exceedingly challenging. Here in , we describe a double-click strategy that enables the sequential ligation of widely available carboxylic acids and amines with fluorosulfuryl isocyanate (FSO 2 NCO) via a modular amidation/SuFEx process. This method provides facile access to chemical libraries of N-fluorosulfonyl amides (RCONHSO 2 F) and N-acylsulfamides (RCONHSO 2 NR ´ R ´´ ) in near-quantitative yields under simple and practical conditions. The robustness and efficiency of this double click strategy is showcased by the facile construction of chemical libraries in 96-well microtiter plates from a large number of carboxylic acids and amines. Preliminary biological activity screening reveals that some compound s  exhibit high antimicrobial activities against Gram-positive bacterium  S. aureus and drug-resistant MRSA (MIC up to 6.25·µg mL-1). These results provide compelling evidence for the potential application of modular click chemistry library as an enabling technology in high-throughput medicinal chemistry.

PIDA-mediated Oxidative Decarboxylation of Oxamic Acids. The Role of Radical Acidity Enhancement.

The PIDA-mediated oxidative decarboxylation of oxamic acids in the presence of alcohols is shown to afford the corresponding urethanes under thermal conditions. Computational and experimental mechanistic exploration allows to rationalize the different reactivity of PIDA as compared to related cyclic BI-OAc and highlights the importance of the enhanced acidity of the proton in the carbamoyl radical intermediate.

"Catch-Store-Release" Strategy for the Stabilization of 4,4'-Methylene Diphenyl Diisocyanate (4,4'-MDI).

4,4'-Methylene diphenyl diisocyanate (MDI) is an industrially crucial compound, being one of the most utilized linkers in the polyurethane industry. However, its long-term stability is limited due to dimerization to form insoluble uretdione. Herein we demonstrate an organometallic "catch-store-release" concept aiming at improving the long-term chemical stability of MDI. Treatment of MDI with two equivalents of selected N-heterocyclic carbenes (NHC) forms stable MDI-NHC adducts. Treatment of the adducts with CuCl forms metastable di-CuI complexes that undergo decomposition to re-form MDI (up to 85 %), along with Cu-NHC complexes. The yield of re-formed MDI can be improved (up to 95 %) by the release of the NHC ligands in the form of thiourea; this prevents subsequent MDI dimerization/polymerization by the carbenes. Furthermore, the need to separate MDI from the reaction mixture can be eliminated by the direct reaction of MDI-NHC complexes with alcohols (as models for diols), that form dicarbamate (as a model for polyurethane) quantitatively.

Innovations in applications and prospects of non-isocyanate polyurethane bioplastics.

Currently, conventional plastics are necessary for a variety of aspects of modern daily life, including applications in the fields of healthcare, technology, and construction. However, they could also contain potentially hazardous compounds like isocyanates, whose degradation has a negative impact on both the environment and human health. Therefore, researchers are exploring alternatives to plastic which is sustainable and environmentally friendly without compromising its mechanical and physical features. This review study highlights the production of highly eco-friendly bioplastic as an efficient alternative to non-biodegradable conventional plastic. Bioplastics are produced from various renewable biomass sources such as plant debris, fatty acids, and oils. Poly-addition of di-isocyanates and polyols is a technique employed over decades to produce polyurethanes (PUs) bioplastics from renewable biomass feedstock. The toxicity of isocyanates is a major concern with the above-mentioned approach. Novel green synthetic approaches for polyurethanes without using isocyanates have been attracting greater interest in recent years to overcome the toxicity of isocyanate-containing raw materials. The polyaddition of cyclic carbonates (CCs) and polyfunctional amines appears to be the most promising method to obtain non-isocyanate polyurethanes (NIPUs). This method results in the creation of polymeric materials with distinctive and adaptable features with the elimination of harmful compounds. Consequently, non-isocyanate polyurethanes represent a new class of green polymeric materials. In this review study, we have discussed the possibility of creating novel NIPUs from renewable feedstocks in the context of the growing demand for efficient and ecologically friendly plastic products.

Chemically Recyclable Biobased Non-Isocyanate Polyurethane Networks from CO2 -Derived Six-membered Cyclic Carbonates.

Non-isocyanate polyurethanes (NIPUs) are widely studied as sustainability potential, because they can be prepared without using toxic isocyanates in the synthesis process. The aminolysis of cyclic carbonate to form NIPUs is a promising route. In this work, a series of NIPUs is prepared from renewable bis(6-membered cyclic carbonates) (iEbcc) and amines. The resulting NIPUs possess excellent mechanical properties and thermal stability. The NIPUs can be remolded via transcarbamoylation reactions, and iEbcc-TAEA-10 (the molar ratio of tris(2-aminoethyl)amine in amines is 10%) still get a recovery ratio of 90% in tensile stress after three cycles of remolding. In addition, the obtained materials can be chemically degraded into bi(1,3-diol) precursors with high purity (>99%) and yield (>90%) through alcoholysis. Meanwhile, the degraded products can be used to regenerate NIPUs with similar structures and properties as the original samples. The synthetic strategy, isocyanate-free and employing isoeugenol and carbon dioxide (CO2 ) as building blocks, makes this approach an attractive pathway to NIPU networks taking a step toward a circular economy.

Paving the Way towards Sustainability of Polyurethanes: Synthesis and Properties of Terpene-Based Diisocyanate.

Due to growing concerns about environmental issues and the decline of petroleum-based resources, the synthesis of new biobased compounds for the polymer industry has become a prominent and timely topic. P-menthane-1,8-diamine (PMDA) is a readily available compound synthesized from turpentine, a cheap mixture of natural compounds isolated from pine trees. PMDA has been extensively used for its biological activities, but it can also serve as a source of valuable monomers for the polymer industry. In this work, commercial PMDA (ca. 85% pure) was purified by salinization, crystallization, and alkali treatment and then converted into p-menthane-1,8-diisocyanate (PMDI) through a phosgene-free synthesis at room temperature. A thorough analytical study using NMR techniques (1H, 13C, 13C-1H HSQC, 13C-1H HMBC, and 1H-1H NOESY) enables the characterization of the cis-trans isomeric mixtures of both PMDA and PMDI. These structural studies allowed for a better understanding of the spatial configuration of both isomers. Then, the reactivity of PMDI with a primary alcohol (benzyl alcohol) was studied in the presence of nine different catalysts exhibiting different activation modes. Finally, the use of PMDI in the synthesis of polyurethanes was explored to demonstrate that PMDI can be employed as a new biobased alternative to petrochemical-based isocyanates such as isophorone diisocyanate (IPDI).

Influence of Phosphorus Structures and Their Oxidation States on Flame-Retardant Properties of Polyhydroxyurethanes.

This article focuses on the synthesis of polyhydroxyurethane (PHU) materials containing novel phosphorus flame retardants (FR). Four different phosphorus compounds were grafted onto cyclic carbonate: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), diethyl phosphite (DEP), diphenyl phosphite (DPP) and dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (BPPO). Thus, three novel phosphorus reactive cyclic carbonates which have never been reported so far were synthetized. Phosphorus FR containing PHU materials were characterized by FTIR to evidence the total conversion of the cyclic carbonate. Moreover, the gel contents up to 80% confirmed the formation of the polymer network. Then, the thermal stability and the flame-retardant properties were investigated by thermogravimetric analyses, cone calorimeter and pyrolysis combustion flow calorimeter. The mode of action of phosphorus compounds, depending on the oxidation state, was especially highlighted. Phosphonate (+III) provided better action in a condensed phase than phosphinate thanks to a more efficient char formation. Among phosphonates, differences were observed in terms of char-formation rate and expansion. DEP provided the best flame-retardant properties, with a reduction of 76% of pHRR with 2 wt% of phosphorus in cone calorimeter analysis. Therefore, this article highlighted the different modes of action of phosphorus flame retardants, depending on the oxidation state of phosphorus, in PHU materials.

Synthesis and Properties of 1,3-Disubstituted Ureas Containing (Adamantan-1-yl)(phenyl)methyl Fragment Based on One-Pot Direct Adamantane Moiety Inclusion.

A one-stage method for the preparation of 1-[isocyanato(phenyl)methyl]adamantane containing a phenylmethylene fragment located between the adamantane fragment and the isocyanate group, and 1-[isocyanato(phenyl)methyl]-3,5-dimethyladamantane with additional methyl groups at the nodal positions of adamantane, with a yield of 95% and 89%, respectively, is described. The method includes the direct inclusion of an adamantane moiety through the reaction of phenylacetic acid ethyl ester with 1,3-dehydroadamantane or 3,5-dimethyl-1,3-dehydroadamantane followed by the hydrolysis of the obtained esters. The reaction of 1-[isocyanato(phenyl)methyl]adamantane with fluorine(chlorine)-containing anilines gave a series of 1,3-disubstituted ureas with 25-85% yield. 1-[Isocyanato(phenyl)methyl]-3,5-dimethyladamantane was involved in the reactions with fluorine(chlorine)-containing anilines and trans-4-amino-(cyclohexyloxy)benzoic acid to obtain another series of ureas with a yield of 29-74%. The resulting 1,3-disubstituted ureas are promising inhibitors of the human soluble epoxide hydrolase (hsEH).

Reactive Disperse Dyes Bearing Various Blocked Isocyanate Groups for Digital Textile Printing Ink.

Wastewater management is of considerable economic and environmental importance for the dyeing industry. Digital textile printing (DTP), which is based on sublimation transfer and does not generate wastewater, is currently being explored as an inkjet-based method of printing colorants onto fabric. It finds wide industrial applications with most poly(ethylene terephthalate) (PET) and nylon fibers. However, for additional industrial applications, it is necessary to use natural fibers, such as cotton. Therefore, to expand the applicability of DTP, it is essential to develop a novel reactive disperse dye that can interact with the fabric. In this study, we introduced a blocked isocyanate functional group into the dye to enhance binding to the fabric. The effect of sublimation transfer on fabrics as a function of temperature was compared using the newly synthesized reactive disperse dyes with different blocking groups based on pyrazole derivatives, such as pyrazole (Py), di-methylpyrazole (DMPy), and di-tert-butylpyrazole (DtBPy). Fabrics coated with the new reactive disperse dyes, including PET, nylon, and cotton, were printed at 190 °C, 200 °C, and 210 °C using thermal transfer equipment. In the case of the synthesized DHP-A dye on cotton at 210 °C, the color strength was 2.1, which was higher than that of commercial dyes and other synthesized dyes, such as DMP-A and DTP-A. The fastness values of the synthesized DHP-A were measured on cotton, and it was found that the washing and light fastness values on cotton are higher than those of commercial dyes. This study confirmed the possibility of introducing isocyanate groups into reactive disperse dyes.

Are (Co)Polymers of 1,1,3,3,3-Pentafluoropropene Possible?

The copolymerization and terpolymerization of 1,1,3,3,3-pentafluoropropene (PFP) with various combinations of fluorinated and hydrogenated comonomers were investigated. The chosen fluoromonomers were vinylidene fluoride (VDF), 3,3,3-trifluoropropene (TFP), hexafluoropropene (HFP), perfluoromethylvinyl ether (PMVE), chlorotrifluoroethylene (CTFE) and tert-butyl-2-trifluoromethacrylate (MAF-TBE), while the hydrocarbon comonomers were vinylene carbonate (VCA), ethyl vinyl ether (EVE) and 3-isopropenyl-α,α-dimethylbenzyl isocyanate (m-TMI). Copolymers of PFP with non-homopolymerizable monomers (HFP, PMVE and MAF-TBE) led to quite low yields, while the introduction of VDF enabled the synthesis of poly(PFP-ter-VDF-ter-M3) terpolymers with improved yields. PFP does not homopolymerize and delays the copolymerizations. All polymers were either amorphous fluoroelastomers or fluorothermoplastics with glass transition temperatures ranging from -56 °C to +59 °C, and they exhibited good thermal stability in air.

Safer Polyurethane Foams with Cyclic Carbonates.

Polyurethanes (PUs) are a class of materials usually synthesized from isocyanates, diols, and water. Water is essential for producing carbon dioxide (CO2 ) which is used for the self-blowing of the foams. Due to safety concerns with the production of isocyanates, alternative chemistries have been evaluated and cyclic carbonate systems have shown great promise. In a recent advancement by Bourguignon, Grignard, and Detrembleur, a cyclic carbonate and diamine system is capable of generating CO2 for self-blowing through hydrolysis of the carbonate-based monomer. The authors demonstrate that with a simple variation of the diamine monomer a wide range of physical and thermo-mechanical properties were achievable. This work represents a significant step towards safer and more environmentally friendly PUs.

Lewis Acid Assisted Brønsted Acid Catalysed Decarbonylation of Isocyanates: A Combined DFT and Experimental Study.

An efficient and mild reaction protocol for the decarbonylation of isocyanates has been developed using catalytic amounts of Lewis acidic boranes. The electronic nature (electron withdrawing, electron neutral, and electron donating) and the position of the substituents (ortho/meta/para) bound to isocyanate controls the chain length and composition of the products formed in the reaction. Detailed DFT studies were undertaken to account for the formation of the mono/di-carboxamidation products and benzoxazolone compounds.

Non-Isocyanate Aliphatic-Aromatic Poly(carbonate-urethane)s-An Insight into Transurethanization Reactions and Structure-Property Relationships.

This study reveals insights into the transurethanization reactions leading to the aliphatic-aromatic non-isocyanate poly(carbonate-urethane)s (NIPCUs) and their structure-property relationships. The crucial impact of the alkyl chain length in 4,4'-diphenylmethylene bis(hydroxyalkyl carbamate) (BHAC) on the process of transurethanization reactions was proved. The strong susceptibility of hydroxyethyl- and hydroxybutyl carbamate moieties to the back-biting side reactions was observed due to the formation of thermodynamically stable cyclic products and urea bonds in the BHACs and NIPCUs. When longer alkyl chains (hydroxypentyl-, hydroxyhexyl-, or hydroxydecyl carbamate) were introduced into the BHAC structure, it was not prone to the back-biting side reaction. Both 1H and 13C NMR, as well as FT-IR spectroscopies, confirmed the presence of carbonate and urethane (and urea for some of the samples) bonds in the NIPCUs, as well as proved the lack of allophanate and ether groups. The increase in the alkyl chain length (from 5 to 10 carbon atoms) between urethane groups in the NIPCU hard segments resulted in the increase in the elongation at break and crystalline phase content, as well as the decrease in the Tg, tensile strength, and hardness. Moreover, the obtained NIPCUs exhibited exceptional mechanical properties (e.g., tensile strength of 40 MPa and elongation at break of 130%).

Total Synthesis of Eliglustat via Diastereoselective Amination of Chiral para-Methoxycinnamyl Benzyl Ether.

Eliglustat (Cerdelga®, Genzyme Corp. Cambridge, MA, USA) is an approved drug for a non-neurological type of Gaucher disease. Herein, we describe the total synthesis of eliglustat 1 starting from readily available 1,4-benzodioxan-6-carbaldehyde via Sharpless asymmetric dihydroxylation and diastereoselective amination of chiral para-methoxycinnamyl benzyl ethers using chlorosulfonyl isocyanate as the key steps. Notably, the reaction between syn-1,2-dibenzyl ether 6 and chlorosulfonyl isocyanate in the mixture of toluene and hexane (10:1) afforded syn-1,2-amino alcohol 5 at a 62% yield with a diastereoselectivity > 20:1. This observation can be explained by competition between the SNi and the SN1 mechanisms, leading to the retention of stereochemistry.

Choline Chloride/Urea Deep Eutectic Solvents: A Promising Reaction Medium for the Synthesis of Bio-Based Poly(hydroxyurethane)s.

The development of more sustainable and eco-friendly polymers has attracted much attention from researchers over the past decades. Among the different strategies that can be implemented towards this goal, the substitution of the toxic reagents/monomers often used in polyurethane chemistry has stimulated much innovation leading to the development of the hydroxylated version of PURs, namely, the poly(hydroxyurethane)s (PHURs). However, some PHURs remain far from being sustainable as their synthesis may involve monomers and/or solvents displaying poor environmental impacts. Herein, we report on the use of more sustainable conditions to synthesize the biobased polycarbonates involved in the aminolysis reaction. In addition, we demonstrate that the use of renewable deep eutectic solvents (DESs) can act both as excellent solvents and organocatalysts to promote the aminolysis reaction.