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Organometallic Compounds as Heterogeneous Catalysts
Published in Varun Rawat, Anirban Das, Chandra Mohan Srivastava, Heterogeneous Catalysis in Organic Transformations, 2022
Garima Sachdeva, Monu Verma, Varun Rawat, Ved Prakash Verma, Manish Srivastava, Sudesh Kumar, Singh Vanshika
Copper is the cheapest and most abundant of the coinage metals, with oxidation states ranging from 0 to +4 [9]. Tremendous advancement has been seen in organic synthesis with copper as a reagent and catalyst in the last few years. Organocopper compounds consist of a carbon–copper chemical bond and provide effective coupling of two different carbon groups. Organocopper reagents are easy to handle, highly reactive, and provide regioselectivity, chemoselectivity, and stereoselectivity; hence, they are utilized in the synthesis of natural products and as intermediates for many reactions.
Structural Design for Molecular Catalysts
Published in Qingmin Ji, Harald Fuchs, Soft Matters for Catalysts, 2019
Qingmin Ji, Qin Tang, Jonathan P. Hill, Katsuhiko Ariga
The use of Cu for cross-coupling reactions actually predates the discovery of Pd as a catalyst [44, 45]. Regardless of the instability of organocopper(I) species and the propensity of various Cu species to undergo radical and disproportionation reactions, Cu salts and complexes currently rank among the most intensively investigated homogeneous catalysts for fine chemical synthesis, owing to low cost and toxicity compared with noble metals as well as to the broad variety of chemical transformations enabled by this metal center.
Diaryl sulfides synthesis: copper catalysts in C–S bond formation
Published in Journal of Sulfur Chemistry, 2019
Lian Chen, Ali Noory Fajer, Zhanibek Yessimbekov, Mosstafa Kazemi, Masoud Mohammadi
Ionic liquids (ILs) are molten salts with melting points at or below 100°C, mainly composed of organic cations and organic or inorganic anions and are thus often specified as room-temperature ionic liquids [75]. Jiang group, reported the synthesis of 3-sulfenylindoles and 3-sulfenylbenzofurans via sulfurization with elemental sulfur in ionic liquids (Scheme 27) [76]. A copper/phenantroline mediated sulfurization of the boronic acid generates an organocopper thiolate complex. After a 5-endo-dig heteropalladation, a transmetallation transfers the thiolate to the organopalladium complex, similarly to the Liebeskind-Srogl cross-coupling. Reductive elimination then forms the product, while the catalyst is reoxidized by Ag(I) to the active Pd(II) species.
Odorless, convenient and one-pot synthesis of thioethers from organic halides and thiourea
Published in Journal of Sulfur Chemistry, 2019
Aazam Monfared, Sheida Ahmadi, Zahra Rahmani, Parvaneh Delir Kheirollahi Nezhad, Akram Hosseinian
One of the first synthesis of thioether derivatives through copper-catalyzed C-S coupling of organic halides with thiourea was reported by Firouzabadi and co-workers in 2010 [25], who treated various aryl halides 5 with alkyl bromides 6 and thiourea in the presence of 5–10 mol% of low-cost commercially available CuI as a catalyst and 4 equiv. of K2CO3 as a base in binary solvent PEG 200 (polyethylene glycol)/H2O 10:1. These three-component reactions were carried out under an inert atmosphere at 80–100°C and provided the expected unsymmetrical aryl alkyl thioethers 7 in moderate to excellent yields (Scheme 1). The results proved that the electron-poor aryl halides give better yields compared to the electron-rich ones. It is noteworthy that both aromatic and heteroaromatic halides are tolerated by the reaction conditions employed. The proposed mechanism of the reaction by the authors is depicted in Scheme 2. First, an S-alkylisothiouronium salt A was formed via the reaction of thiourea with alkyl bromide 6. This intermediate underwent hydrolysis to generate the thiolate intermediate B and urea. Subsequently, the oxidative addition of this intermediate to copper catalyst yielded organocopper intermediate C. Next, the reaction of intermediate C with aryl halide 5 in the presence of the base generated the intermediate D. Finally, reductive elimination of D afforded the expected thioether 7. Shortly afterwards, the same research team found that treatment of phenolic esters (e.g. acetates, triflates, tosylates and phosphonates) with alkyl halides (iodides, bromides, and chlorides) and thiourea under standard reaction conditions, afforded corresponding aryl alkyl thioethers in good to excellent yields [26]. The author showed that their methodology can also be scaled up to provide multigram quantities of the desired thioethers without sacrificing product yield.
A walk around the decarboxylative C-S cross-coupling reactions
Published in Journal of Sulfur Chemistry, 2019
Akram Hosseinian, Parvaneh Delir Kheirollahi Nezhad, Sheida Ahmadi, Zahra Rahmani, Aazam Monfared
The first example of metal-catalyzed decarboxylative C-S cross-coupling reaction between carboxylic acids and thiols was reported by Xiaogang Liu and his team in 2009; a broad range of carboxylic acids 1 (aromatic, heteroaromatic, and cinnamic acids) were reacted with various aromatic and aliphatic thiols 2 at 160°C in the presence of Pd(OAc)2/CuCO3+Cu(OH)2/KF combination as a catalytic system and afforded the corresponding aryl sulfide derivatives 3 in 24 hours (Scheme 1(a)) [25]. The results proved that the yields in this coupling reaction were strongly dependent on the electronic character and substitution pattern of the substituents in the phenyl ring periphery of carboxylic acids. While benzoic acids with strongly electron-withdrawing substituents in the ortho-position gave the desired products in good to high yields, benzoic acids with strongly electron-donating substituents in the same position failed to afford the product. In addition, the use of benzoic acids without a substituent or with a para-substituent gave the expected coupling products in low to moderate yields. This decarboxylative coupling reaction is equally effective for both aromatic and aliphatic thiols. Importantly, this C-S coupling strategy can be successfully extended to disulfides. The authors nicely applied their protocol for the synthesis of a benzothiazole compound 5 (Scheme 1(b)). The authors proposed mechanism of this decarboxylative C-S cross-coupling is depicted in Scheme 2. Initially, thiolate A (generated from deprotonation of starting thiol 2 with a base) reacts with the palladium catalyst to form intermediate B. Meanwhile, the reaction of carboxylic acids 1 with copper gives organocopper intermediate C through a decarboxylation process. This intermediate C upon transmetalation into intermediate B leads to the palladium(II) species D. Finally, reductive elimination of intermediate D affords the observed sulfides 3.