- Facile access to imidazole derivatives: Carboxylic acids and δ-lactones
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The nucleophilic addition of bis-(TMS)ketene acetals to doubly N-activated imidazole under mild conditions, leads to their corresponding dihydroimidazolyl carboxylic acids in a first instance. Subsequent reaction of these acids can be efficiently turned i
- Rivera-Hernández, Alejandro,López-Jimeno, Isabel S.,Carmona-Reyes, Genaro A.,Alfredo-Toscano,Penieres-Carrillo, José Guillemo,álvarez-Toledano, Cecilio
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- Palladium-Catalyzed Oxidative C–H Alkoxycarbonylation of Arenes with Alkylcarbazates Directed by N-Heterocyclic Substituents
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With alkyl carbazates as the green ester source, a novel palladium-catalyzed oxidative free radical carbonylative transformation of the C–H bond on aromatic rings to produce esters has been developed. Good yields of the corresponding products have been obtained with wide functional group tolerance and excellent regioselectivity. A variety of alkyl carbazates are found to be suitable reactants for the ortho-alkoxycarbonylation on the aromatic ring.
- Yogesh Kumar, Gujjenahalli Ramalingaiah,Begum, Noor Shahina
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supporting information
p. 4698 - 4704
(2020/07/04)
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- Enantioselective Syntheses of Strychnos and Chelidonium Alkaloids through Regio- and Stereocontrolled Cooperative Catalysis
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We describe enantioselective syntheses of strychnos and chelidonium alkaloids. In the first case, indole acetic acid esters were established as excellent partner nucleophiles for enantioselective cooperative isothiourea/Pd catalyzed α-alkylation. This provides products containing indole-bearing stereocenters in high yield and with excellent levels of enantioinduction in a manner that is notably independent of the N-substituent. This led to concise syntheses of (?)-akuammicine and (?)-strychnine. In the second case, the poor performance of ortho-substituted cinnamyl electrophiles in the enantioselective cooperative isothiourea/Ir catalyzed α-alkylation was overcome by appropriate substituent choice, leading to enantioselective syntheses of (+)-chelidonine, (+)-norchelidonine, and (+)-chelamine.
- Fyfe, James W. B.,Hutchings-Goetz, Luke S.,Snaddon, Thomas N.,Yang, Chao
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supporting information
p. 17556 - 17564
(2020/08/14)
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- One-pot protection-glycosylation reactions for synthesis of lipid II analogues
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(2,6-Dichloro-4-methoxyphenyl)(2,4-dichlorophenyl)methyl trichloroacetimidate (3) and its polymer-supported reagent 4 can be successfully applied to a one-pot protection-glycosylation reaction to form the disaccharide derivative 7 d for the synthesis of lipid II analogues. The temporary protecting group or linker at the C-6 position and N-Troc protecting group of 7 d can be cleaved simultaneously through a reductive condition. Overall yields of syntheses of lipid II (1) and neryl-lipid II Nε-dansylthiourea are significantly improved by using the described methods. Sweet synthetic methods: A one-pot protection glycosylation reaction of the diol glycosyl acceptor is developed for synthesis of the lipid II disaccharide (see figure, Troc=2,2,2-trichloroethoxycarbonyl). Improved syntheses of lipid II and neryl-lipid II analogues are summarized.
- Mitachi, Katsuhiko,Mohan, Priya,Siricilla, Shajila,Kurosu, Michio
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supporting information
p. 4554 - 4558
(2014/05/06)
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- Palladium-catalyzed C3-benzylation of indoles
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A general method for regioselective C3-benzylation of indoles has been developed. Various 3-substituted indoles and benzyl methyl carbonates with different electronic properties react under mild conditions to afford a diverse range of 3-benzylindolenine products in good yields.
- Zhu, Ye,Rawal, Viresh H.
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supporting information; experimental part
p. 111 - 114
(2012/03/07)
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- On the reactivity of imidazole carbamates and ureas and their use as esterification and amidation reagents
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The optimization, substrate scope, and mechanism of esterification and amidation of carboxylic acids mediated by imidazole-based reagents are discussed. The innate reactivity of carbonylimidazole reagents with a range of nucleophiles is also explored. New reagents developed for the synthesis of α,β-unsaturated esters are described, as are reagents for the preparation of tertiary amides directly from carboxylic acids.
- Heller, Stephen T.,Sarpong, Richmond
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body text
p. 8851 - 8859
(2011/12/02)
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- Chemoselective esterification and amidation of carboxylic acids with imidazole carbamates and ureas
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Imidazole carbamates and ureas were found to be chemoselective esterification and amidation reagents. A wide variety of carboxylic acids were converted to their ester or amide analogues by a simple synthetic procedure in high yields.
- Heller, Stephen T.,Sarpong, Richmond
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supporting information; experimental part
p. 4572 - 4575
(2010/12/25)
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- Direct N-carbamoylation of 3-monosubstituted oxindoles with alkyl imidazole carboxylates
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(Chemical Equation Presented) Regioselective N-carbamoylation of oxindoles was achieved through the use of imidazole carboxylate reagents. This reaction provides ready access to N-carbamoyl-3-monosubstituted oxindoles.
- Trost, Barry M.,Zhang, Yong,Zhang, Ting
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experimental part
p. 5115 - 5117
(2009/10/24)
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- Electroreductive acylation of aromatic imines with acylimidazoles
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The intermolecular reductive coupling of aromatic imines with acylimidazoles was effected by electroreduction in the presence of chlorotrimethylsilane and gave α-amino-α-aryl ketones. This method was also effective for the synthesis of α-amino-α-aryl esters using methoxycarbonylimidazole as an electrophile.
- Kise, Naoki,Morimoto, Shinji
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p. 1765 - 1771
(2008/09/18)
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- Electroreductive acylation of aromatic ketones with acylimidazoles
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The intermolecular reductive coupling of aromatic ketones with acylimidazoles was effected by electroreduction in the presence of chlorotrimethylsilane and gave α-trimethylsiloxy ketones and esters. The best result was obtained using Bu4NPF6 as a supporting electrolyte and a Pb cathode in THF. The α-trimethylsiloxy-containing products were transformed to the corresponding α-hydroxy ketones and esters by treatment with TBAF in THF. This method was also effective for the intramolecular reductive coupling of δ- and ε-keto acylimidazoles.
- Kise, Naoki,Agui, Syun,Morimoto, Shinji,Ueda, Nasuo
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p. 9407 - 9410
(2007/10/03)
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- ACYCLIC CARBONATES OF β-CYCLODEXTRIN
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The synthesis of acyclic carbonates of β-cyclodextrin obtained from the reaction of alkyloxycarbonylimidazole with β-cyclodextrin, is described.The reaction gave a mixture of linear carbonates which were characterized via TLC, HPLC, 13C NMR and FT-IR.No cyclic carbonates have been detected.The products obtained are low-melting, surface active, easily soluble in water and show good inclusion properties.Their average degree of substitution varies depending on the reaction conditions used.
- Trotta, Francesco,Moraglio, Giovanni,Marzona, Mario,Maritano, Silvana
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p. 559 - 562
(2007/10/02)
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- Alkylation, Acylation and Silylation of Azoles
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Performing alkylation, acylation and silylation reactions in separate deprotonation and nucleophilic displacement steps allows for better control of reaction conditions and facilitates problem handling in these processes.In the alkylation of azoles the alkylating agents and solvents possess individual reaction capabilities which seem to be approximately additive.Monoalkylation occurs if the sum of the normalized reaction potentials is equal or larger than the pKa value of the azole.Dialkylation is avoided by keeping the sum of the normalized reaction potentials below the pKa value of the alkylazole.The applicability of these principles is demonstrated by the development of effective procedures for the methylation, benzylation, acetylation, methoxycarbonylation and trimethylsilylation of azoles.
- Begtrup, Mikael,Larsen, Peter
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p. 1050 - 1057
(2007/10/02)
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- α-Nitro Ketones and Esters from Acylimidazoles
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The anion of 2-(2-nitroethyl)-1,3-dioxolane (4), prepared from the corresponding 2-bromo compound (3), undergoes condensation with acylimidazoles to give the 3-nitro-4-oxobutanal acetals (9), which can serve as valuable polyfunctional intermediates.Condensation with 1-(methoxyoxalyl)imidazole gives the tetrafunctionalized methyl 4-(1,3-dioxolan-2-yl)-3-nitro-2-oxobutanoate (13), which, however, decomposed on attempted deprotection of the ester function.The syntheses in excellent yields of simple α-nitro ketones and α-nitro esters from acylimidazoles and nitroethane and 2-nitropropane are also described.
- Crumbie, Robyn L.,Nimitz, Jonathan S.,Mosher, Harry S.
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p. 4040 - 4045
(2007/10/02)
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