Cyclic Thiocarbonates Research Articles

Bifunctional Onium and Potassium Iodides as Nucleophilic Catalysts for the Solvent-Free Syntheses of Carbonates, Thiocarbonates, and Oxazolidinones from Epoxides.

The catalytic potential of organo-onium iodides as nucleophilic catalysts is aptly demonstrated in the synthesis of cyclic carbonates from epoxides and carbon dioxide (CO2 ), as a representative CO2 utilization reaction. Although organo-onium iodide nucleophilic catalysts are metal-free environmentally benign catalysts, harsh reaction conditions are generally required to efficiently promote the coupling reactions of epoxides and CO2 . To solve this problem and accomplish efficient CO2 utilization reactions under mild conditions, bifunctional onium iodide nucleophilic catalysts bearing a hydrogen bond donor moiety were developed by our research group. Based on the successful bifunctional design of the onium iodide catalysts, nucleophilic catalysis using a potassium iodide (KI)-tetraethylene glycol complex was also investigated in coupling reactions of epoxides and CO2 under mild reaction conditions. These effective bifunctional onium and potassium iodide nucleophilic catalysts were applied to the solvent-free syntheses of 2-oxazolidinones and cyclic thiocarbonates from epoxides.

Highly selective solvent free catalysis of CO2 and CS2 fixation under mild conditions using electronically varied zinc complexes

Electronically varied Zn complexes as a common catalytic platform to activate CO2 and CS2 under mild and solvent-free conditions, which selectively yielded cyclic carbonates or cyclic thiocarbonates.

Synthesis and applications of the sulfur containing analogues of cyclic carbonates.

Cyclic thiocarbonates are the sulfur containing analogues of the well-studied cyclic carbonates and are relatively poorly explored despite their potential applications and intriguing reactivities. To date, application of these organosulfur compounds has included their use as monomers for polythiocarbonate synthesis (their ring-opening is more readily achieved and more selective than the corresponding cyclic carbonates) and as reactive intermediates for the preparation of a range of higher-value sulfur containing compounds. Despite these uses, the synthesis of these compounds is far less explored and developed than their non-sulfur analogues. Here, we provide an overview of the state-of-the-art, both recent and historical, for the synthesis of a range of cyclic mono-, di- and tri-thiocarbonates (both five and six-membered rings), with selected examples of their reported applications also highlighted.

Copolymerization of Carbonyl Sulfide and Propylene Oxide via a Heterogeneous Prussian Blue Analogue Catalyst with High Productivity and Selectivity.

This study demonstrates the superiority of a stable and well-defined heterogeneous cobalt hexacyanocobaltate (Co3 [Co(CN)6 ]2 ), a typical cobalt Prussian Blue Analogue (CoCo-PBA) that catalyzes the copolymerization of carbonyl sulfide (COS) and propylene oxide (PO) to produce poly(propylene monothiocarbonate)s (PPMTC). The number-average molecular weights of the PPMTC were 66.4 to 139.4 kg/mol, with a polydispersity of 2.0-3.9. The catalyst productivity reached 1040 g polymer/g catalyst (12.0 h). The oxygen-sulfur exchange reaction (O/S ER), which would generate random thiocarbonate and carbonate units, was effectively suppressed, and thus the selectivity of the monothiocarbonate over carbonate linkages was up to >99%. It was shown that no cyclic thiocarbonate byproduct was produced during the heterogeneous catalysis of COS/PO copolymerization using CoCo-PBA as the catalyst. The content of monothiocarbonate and ether units in the copolymer chain could be regulated by tuning the feeding amount of COS.

High-Performance Nonisocyanate Thermoplastic Polythiourethane with High Hydrogen Bond Content

Nonisocyanate polyurethane (NIPU) has been extensively studied because of its sustainability potential. However, the low reactivity of five-membered cyclocarbonates with amines and the side reactions at higher temperatures always sacrifice the performance of NIPUs. In this work, a bisphenol-S cyclic thiocarbonate and different amino-terminated dimer-acid polyamides (DAPAs) were used to prepare nonisocyanate polythiourethanes (SPTU-DAs). Wherein bisphenol-S acts as a hard segment due to a π-π package, plentiful hydrogen bonds introduced by DAPA units induce crystallization and nanophase separation. They both endow the NIPUs with high mechanical performance. Meanwhile, active cyclic thiocarbonate, instead of cyclic carbonate, ensures rapid synthesis under mild conditions without side reactions. The experimental results of DSC, WAXD, and DMA confirmed the existence of crystallization of SPTU-DAs. The as-prepared thermoplastic polythiourethane has a maximum strength of more than 10 MPa, which is stronger than those of the cross-linked nonisocyanate polythiourethanes reported. It is of key significance to obtain the high performance of nonisocyanate polythiourethanes.

Facile Access to Functionalized Poly(thioether)s via Anionic Ring-Opening Decarboxylative Polymerization of COS-Sourced α-Alkylidene Cyclic Thiocarbonates

Herein, a series of α-alkylidene cyclic thiocarbonates (αCTCs) have been selectively synthesized from carbonyl sulfide (COS) and primary propargylic alcohols and polymerized via anionic ring-openin...

An Investigation on the Production of Random Copolymer with Monothiocarbonate and Trithiocarbonate Units over Cyclic Thiocarbonate via Metal‐free Catalysis

Summary of main observation and conclusionSynthesis of poly(thiocarbonate)s from the copolymerization of epoxides and carbon disulfide (CS2) remains a tough challenge, due to inevitable oxygen‐sulfur atom scrambling process. In this work, we utilized the oxygen‐sulfur exchange reaction (O‐S ER) to synthesize a random copolymer with monothiocarbonate and trithiocarbonate units from CS2 and phenyl glycidyl ether (PGE) via metal‐free Lewis pairs. The copolymers contained monothiocarbonate and trithiocarbonate units of which the molar fraction could be tuned by varying either the types of Lewis pairs or the reaction temperature. Keeping track on the intermediate provided an insight in the process of O‐S ER and thus gave a hint to control the product structure. Production and consumption of phenyl thioglycidyl ether was the key process to regulate the chain structure. Remarkably, the oxygen atoms of PGE could be excluded out of the chain, resulting in the nearly complete production of poly(trithiocarbonate)s. Correspondingly, the refractive index of this kind of copolymer could be regulated in a wide range of 1.73—1.79 (at 590 nm).

Poly(thioether)s from Closed-System One-Pot Reaction of Carbonyl Sulfide and Epoxides by Organic Bases.

The synthesis of poly(thioether), a highly desired sulfur-containing polymer, is still a key challenge. Herein, we report a simple and facile approach to poly(thioether)s by closed-system one-pot reaction of carbonyl sulfide (COS) and epoxides. This route underwent the coupling reaction of COS with epoxides, followed by decarboxylative ring-opening polymerization (ROP) of the generated mixed cyclic thiocarbonates with releasing of CO2 and a little bit of COS. Organic base was used as catalyst and initiator in the two steps, respectively. The oxygen/sulfur exchange reaction was driven by successive regioselective elementary reactions and spontaneous releasing of CO2(COS), leading to the sulfur atom of COS transferring to poly(thioether)s, which was well demonstrated by DFT studies. This work provides an easy-to-handle, metal-free route to poly(thioether)s bearing diverse structures by using readily available chemicals.

KI–Tetraethylene Glycol Complex as an Effective Catalyst for the Synthesis of Cyclic Thiocarbonates from Epoxides and CS2

An efficient synthesis of cyclic thiocarbonates from epoxides and CS2 under mild reaction conditions was achieved when a KI–tetraethylene glycol complex was used as a readily available and economic catalyst. The effects of various glycols and alkali metal halides were investigated in the present work to clarify the importance of both KI and tetraethylene glycol. The reaction mechanisms for the synthesis of cyclic thiocarbonates are discussed on the basis of the stereochemistry of the products.

Electrochemical Corey-Winter reaction. Reduction of thiocarbonates in aqueous methanol media and application to the synthesis of a naturally occurring α-pyrone.

An electrochemical version of the Corey–Winter reaction was developed giving excellent results in aqueous methanol media (MeOH/H2O (80:20) with AcOH/AcONa buffer 0.5 M as supporting electrolyte), using a reticulated vitreous carbon as cathode in a divided cell. The electrochemical version is much more environmentally friendly than the classical reaction, where a large excess of trialkyl phosphite as reducing agent and high temperatures are required. Thus, cathodic reduction at room temperature of two cyclic thiocarbonates (−1.2 to −1.4 V vs Ag/AgCl) afforded the corresponding alkenes, trans-6-(pent-1-enyl)-α-pyrone and trans-6-(pent-1,4-dienyl)-α-pyrone, which are naturally occurring metabolites isolated from Trichoderma viride and Penicillium, in high chemical yield and with excellent stereo selectivity.

Synthesis of Cyclic Thiocarbonates from Thiiranes and CS2 with Silica-Immobilized Catalysts

The synthesis of cyclic thiocarbonates by the cycloaddition of carbon disulfide (CS2) to thiiranes in the presence of silica-immobilized amine catalysts was investigated. The catalytic activities of the silica-immobilized catalysts toward the synthesis of cyclic thiocarbonates were higher than the activities of their homogeneous counterparts. The silica-supported catalysts strongly accelerated the cycloaddition of CS2 to thiiranes, and the pseudo-first-order rate constant of the silica-immobilized catalyst was about 430 times larger than that of the corresponding homogeneous catalyst. The coexistence of the molecular catalyst species and the neighboring surface silanols on the catalyst support was found to be key to the reaction acceleration. In addition to providing improved catalytic activity, the solid-supported catalysts were also shown to be recyclable and reusable for at least five cycles.

A Highly Regioselective Palladium‐Catalyzed O,S Rearrangement of Cyclic Thiocarbonates

This work describes an operationally simple catalytic synthesis of cyclic S‐thiocarbonates with predictable regioselectivity in good yields. The reaction utilizes substrates derived from ubiquitous 1,2‐diols in an atom economical intramolecular rearrangement, catalysed by an inexpensive and simple catalyst–ligand system. A crystal structure is presented that clearly confirms the regioselectivity of the reaction.

Poly(monothiocarbonate)s from the Alternating and Regioselective Copolymerization of Carbonyl Sulfide with Epoxides.

Carbonyl sulfide (COS) is an air pollutant that causes acid rain, ozonosphere damage, and carbon dioxide (CO2) generation. It is a heterocumulene and structural analogue of CO2. Relevant to organic synthesis, it is a source of C═O or C═S groups and thus an ideal one-carbon (C1) building block for synthesizing sulfur-containing polymers through the similar route of CO2 copolymerization. In contrast, traditional synthesis of sulfur-containing polymers often involves the condensation of thiols with phosgene and ring-opening polymerization of cyclic thiocarbonates that are generally derived from thiols and phosgene; thus, COS/epoxide copolymerization is a "greener" route to supplement or supplant current processes for the production of sulfur-containing polymers. This Accounts highlights our efforts on the discovery of the selective formation of poly(monothiocarbonate)s from COS with epoxides via heterogeneous zinc-cobalt double metal cyanide complex (Zn-Co(III) DMCC) and homogeneous (salen)CrX complexes. The catalytic activity and selectivity of Zn-Co(III) DMCC for COS/epoxide copolymerization are similar to those for CO2/epoxide copolymerization. (salen)CrX complexes accompanied by onium salts exhibited high activity and selectivity for COS/epoxide copolymerization under mild conditions, affording copolymers with >99% monothiocarbonate units and high tail-to-head content up to 99%. By way of contrast, these catalysts often show moderate or low activity for CO2/epoxide copolymerization. Of note, a specialty of COS/epoxide copolymerization is the occurrence of an oxygen-sulfur exchange reaction (O/S ER), which may produce carbonate and dithiocarbonate units. O/S ER, which are induced by the metal-OH bond regenerated by chain transfer reactions, can be kinetically inhibited by changing the reaction conditions. We provide a thorough mechanistic understanding of the electronic/steric effect of the catalysts on the regioselectivity of COS copolymerization. The regioselectivity of the copolymerization originates from the solely nucleophilic attack of the sulfur anion to methylene of the epoxide, and thus, the chiral configuration of the monosubstituted epoxides is retained. COS-based copolymers are highly transparent sulfur-containing polymers with excellent optical properties, such as high refractive index and Abbe number. Thanks to their good solubility and many available epoxides, COS/epoxide copolymers can potentially be a new applicable optical material. Very recently, crystalline COS-based polymers with or without chiral carbons have been synthesized, which may further expand the scope of application of these new materials.

Comparison of tris(dimethylphenylsilyl)methyllithium and tris(trimethylsilyl)methyllithium reactions with carbon disulfide: a new route for the synthesis of some 1,1-bis(benzylthio)- and bis(allylthio)-2,2-bis(dimethylphenylsilyl)ethenes

A series of bis(benzylthio)- and bis(allylthio)-2,2-bis(dimethylphenylsilyl) ethenes has been obtained by the reaction of (PhMe2Si)3CLi and CS2 with benzyl and allyl bromides. A plausible mechanism for the formation of these compounds has been proposed. The reactivity of (PhMe2Si)3CLi toward CS2 has been compared with that of (Me3Si)3CLi. The reaction of (PhMe2Si)3CLi with CS2 and 2-methyloxirane gave a cyclic thiocarbonate.

A versatile method to prepare difluorinated primary alcohols and its application to the syntheses of novel acyclic fluorinated nucleosides

The addition of fluorine to a molecule often leads to intriguing changes in the properties of the molecule. Many novel drug leads and drug candidates are the results of the incorporation of fluorine. This Letter presents a versatile method to create molecules with the general structure R1R2CHCF2CH2OH from ketone R1(CO)R2. The key steps of this synthetic method involve the formation of a cyclic thiocarbonate and the regioselective radical opening of the thiocarbonate to yield the corresponding primary alcohol –CF2CH2OH. Using this synthetic method, novel fluorinated analogs of ganciclovir and penciclovir have been prepared.

Rate Coefficients for Intramolecular Homolytic Substitution of Oxyacyl Radicals at Sulfur

It is predicted on the basis of ab initio and density functional calculations that intramolecular homolytic substitution of oxyacyl radicals at the sulfur atom in ω-alkylthio-substituted radicals do not involve hypervalent intermediates. With tert-butyl as the leaving radical, free energy barriers ΔG‡ (G3(MP2)-RAD) for these reactions range from 45.8 kJ mol–1 for the formation of the five-membered cyclic thiocarbonate (8) to 56.7 kJ mol–1 for the formation of the six-membered thiocarbonate (9). Rate coefficients in the order of 104–106 s–1 and 101–104 s–1 for the formation of 8 and 9, respectively, at 353.15 K in the gas phase are predicted at the G3(MP2)-RAD level of theory.

Investigations into the coupling of cyclohexene oxide and carbon disulfide catalyzed by (salen)CrCl. Selectivity for the production of copolymers vs. cyclic thiocarbonates

The synthesis of poly(thiocarbonates) has been achieved via the (salen)CrCl/[PPN]Cl (salen = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-ethylenediamino) and PPN(+) = bis(triphenyl-phosphoranylidene)ammonium) catalyzed coupling of carbon disulfide and cyclohexene oxide. Optimal catalytic activity was observed at 50 degrees C and a 1:1 carbon disulfide to cyclohexene oxide loading ratio to afford copolymers with molecular weights ranging from 14,000-34,000 g mol(-1) with narrow molecular weight distributions. The exchange of sulfur and oxygen atoms was observed in both the copolymer and cyclic products. In situ infrared monitoring of the coupling reactions revealed an initiation period followed by formation of copolymers enriched in oxygen content, and concomitantly cyclic thiocarbonates enriched in sulfur content. By way of contrast, the copolymerization of cyclohexene sulfide and carbon disulfide was found to be highly selective and effective for producing cyclohexylene trithiocarbonate vs. the all-sulfur copolymer at 30 degrees C. Density functional theory calculations were carried out on the possible cyclic materials from the coupling of cyclohexene oxide and CS(2), which revealed cyclohexylene trithiocarbonate to be the most stable cyclic species.

Enantioselective Total Synthesis of (+)‐Ottelione A, (−)‐Ottelione B, (+)‐3‐epi‐Ottelione A and Preliminary Evaluation of Their Antitumor Activity

Enantioselective total synthesis of (+)-ottelione A (1) and (-)-ottelione B (2), novel and potent antitumor agents from a freshwater plant, and (+)-3-epi-ottelione A (3), the earlier proposed stereostructure of 1, was efficiently achieved starting from the known tricyclic compound 10. The synthesis involved the following key steps: i) coupling reactions of aldehydes 8 and 9 with the aromatic portion 7 (8+7-->15 and 9+7-->27), ii) base-induced hemiacetal-opening/epimerization reactions of the cyclic hemiacetals 6 and 27 (6-->17 and 27 a-->26 a), and iii) Corey-Winter's reductive olefination of the cyclic thiocarbonates 21 and 36 (21-->22 and 36-->37). The present total synthesis fully established the absolute configuration of these natural products. The cell growth inhibition profile, COMPARE analysis, and tubulin inhibitory assay of (+)-3-epi-ottelione A (3) and its O-acetyl derivative 24 demonstrated that these unnatural substances could be prominent lead compounds for the development of anticancer agents with a novel mode of action.

Synthesis and Biological Evaluation of 2′‐3′‐Didehydro‐2′,3′‐dideoxy‐9‐deazaguanosine, a Monophosphate Prodrug and Two Analogues, 2′,3′‐Dideoxy‐9‐deazaguanosine and 2′,3′‐Didehydro‐2′,3′‐dideoxy‐9‐deazainosine.

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Electrochemical partial fluorination of organic compounds: 82: Anodic α-fluorination of five-membered cyclic thiocarbonates

Anodic fluorination of various kinds of five-membered cyclic thiocarbonates was carried out under various electrolytic conditions and the corresponding α-monofluorinated products were obtained in the cases of 1,3-oxathiolane-2-one and 1,3-dithiolane-2-one with high regioselectivity. On the contrary, oxidative desulfurization of cyclic thiocarbonates with a C S bond took place to provide the corresponding gem-difluorinated product and/or carbonyl compounds depending on the molecular structures of the starting thiocarbonates.