- 4,5,6,7-Tetrachlorobenzo[d][1,3,2]dioxaborol-2-ol as an effective catalyst for the amide condensation of sterically demanding carboxylic acids
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4,5,6,7-Tetrachlorobenzo[d][1,3,2]dioxaborole (4a) and 4,5,6,7- tetrachlorobenzo[d][1,3,2]dioxaborol-2-ol (4b) are effective catalysts for the dehydrative amide condensation between an equimolar mixture of carboxylic acids and amines. In particular, these catalysts are greatly superior to 3,5-bis(trifluoromethyl)phenylboronic acid (1) for the amide condensation of sterically demanding carboxylic acids. In contrast, 4c, which is prepared from a 1:2 molar mixture of B(OH)3 and tetrachlorocatechol, is effective as a Lewis acid-assisted Bronsted acid (LBA) catalyst for Ritter reaction.
- Maki, Toshikatsu,Ishihara, Kazuaki,Yamamoto, Hisashi
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- Ritter reactions in flow
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Flow me a Ritter: Ritter reactions are performed in a simple microreactor setup using tert-butylacetate as versatile carbocation source. The protocol avoids the handling of large amounts of hot concentrated sulfuric acid as low concentrations are optimal for rapid access tert-butyl- or diphenylmethyl- protected amides. Copyright
- Audiger, Logan,Watts, Kevin,Elmore, Simon C.,Robinson, Richard I.,Wirth, Thomas
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- Tropylium-promoted Ritter reactions
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The Ritter reaction used to be one of the most powerful synthetic tools to functionalize alcohols and nitriles, providing valuableN-alkyl amide products. However, this reaction has not been frequently used in modern organic synthesis due to its employment of strongly acidic and harsh reaction conditions, which often lead to complicated side reactions. Herein, we report the development of a new method using salts of the tropylium ion to promote the Ritter reaction. This method works well on a range of alcohol and nitrile substrates, giving the corresponding products in good to excellent yields. This reaction protocol is amenable to microwave and continuous flow reactors, offering an attractive opportunity for further applications in organic synthesis.
- Doan, Son H.,Hussein, Mohanad A.,Nguyen, Thanh Vinh
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- Synthesis of n-benzhydrylamides from nitriles by ritter reactions in formic acid
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Benzhydrol reacts with nitriles in refluxing formic acid to produce amides arising from the Ritter reaction. This reaction does not require a strong acid catalyst, and the products are isolated without the need for chromatography. The conditions permit the preparation of acrylamides and methacrylamides without polymerization of the nitrile.
- Gullickson, Glen C.,Lewis, David E.
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- Environmentally Benign Ritter Reaction Using Bismuth Salts as a Catalyst
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We developed an environmentally benign Ritter reaction of alcohols with nitriles using a commercially available bismuth salt as a less harmful catalyst. The detailed reaction profiles revealed that consumption of the ether by-product as the reaction proceeded was the key for optimizing this reaction, and the yield of the target amide was improved by adding a small amount of water. This finding clearly reveals the significance of using a bismuth salt as the catalyst, as it is not deactivated in the presence of water. This catalyst system has a broad substrate scope, and even with 1 mol-% of the catalyst, the reaction progresses smoothly. It is also possible to react stoichiometric amounts of nitriles and alcohols, thus reducing the amount of organic solvent required for the reaction. Furthermore, as the inexpensive bismuth catalyst can be easily removed using aqueous hydrochloric acid, a purification process that only required washing and drying without any organic solvents was successfully established.
- Ueno, Masaharu,Kusaka, Ryo,Ohmura, Satoshi D.,Miyoshi, Norikazu
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- Aminolysis of N-Acylpyrazoles
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1-Acylpyrazoles reacted with amines having a tiny substituted to afford the corresponding amides.The aminolysis with bulky amines was controlled to be retarded by the steric factors.Due to this steric interaction, the stereoselective aminolysis was observed.This selectivity of aminolysis should increase the utility of pyrazoles as auxiliary compounds in the synthetic loop.
- Kashima, Choji,Fukuchi, Iwao,Takahashi, Katsumi,Hosomi, Akira
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- Silica boron-sulfuric acid nanoparticles (SBSANs): Preparation, characterization and their catalytic application in the Ritter reaction for the synthesis of amide derivatives
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Among a number of different heterogeneous and homogeneous catalysts, silica boron-sulfuric acid nanoparticles (SBSANs) with both protic and Lewis acidic sites were shown to be the most active and recyclable catalyst in the Ritter reaction. Various amide d
- Khalafi-Nezhad, Ali,Foroughi, Habib Ollah,Doroodmand, Mohammad Mahdi,Panahi, Farhad
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experimental part
p. 12842 - 12851
(2012/01/14)
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- Gold catalysis: Alkyl migration in the addition of alcohols to nitriles
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Benzhydroles and nitriles upon gold-catalysed conversion deliver symmetrical ethers and/or N-substituted carboxylic amides. While with most phosphane ligands tested, the dominating product is always the ether, with the trimesitylene ligand the amides are the major products. The reaction conditions are much milder than those reported previously. Mechanistic control experiments with a chiral alcohol prove the intermediacy of carbenium ions, further studies with not readily ionisable alcohols indicate that for the benzhydroles the carbenium ions and gold(I)-hydroxy complexes are intermediates.
- Ibrahim, Nada,Hashmi, A. Stephen K.,Rominger, Frank
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experimental part
p. 461 - 468
(2011/04/16)
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- New boron(III)-catalyzed amide and ester condensation reactions
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In 1996, we reported that benzeneboronic acids bearing electron-withdrawing groups at the meta- or para-position are highly effective catalysts for the amide condensation reaction in less-polar solvents. In this paper, we report that N-alkyl-4-boronopyridinium halides are more effective catalysts than the previous ones in more polar solvents. N-Alkyl-4-boronopyridinium halides are effective not only for amide condensation between equimolar mixtures of carboxylic acids and amines but also for the esterification of α-hydroxycarboxylic acids in alcohol solvents. Furthermore, perchlorocatecholborane is more effective than areneboronic acids for the amide condensation of sterically demanding carboxylic acids. In addition, Lewis acid-assisted Br?nsted acid (LBA), which is prepared from a 1:2 M mixture of boric acid and tetrachlorocatechol, is effective for the Ritter reaction from alcohols and nitriles to amides.
- Maki, Toshikatsu,Ishihara, Kazuaki,Yamamoto, Hisashi
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p. 8645 - 8657
(2008/02/08)
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