- Carboxylation of indoles and pyrroles with CO2 in the presence of dialkylaluminum halides
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The Lewis acid-mediated carboxylation of arenes with CO2 has been successfully applied to 1-substituted indoles and pyrroles by using dialkylaluminum chlorides instead of aluminum trihalides. Thus, the carboxylation of 1-methylindoles, 1-benzyl-, and 1-phenylpyrroles proceeds regioselectively with the aid of an equimolar amount of Me2AlCl under CO2 pressure (3.0 MPa) at room temperature to afford the corresponding indole-3-carboxylic acids and pyrrole-2-carboxylic acids in 61-85% yields, while the same treatment of 1,2,5-trimethylpyrrole affords the 3-carboxylic acid in 52% yield.
- Nemoto, Koji,Onozawa, Satoru,Egusa, Naoki,Morohashi, Naoya,Hattori, Tetsutaro
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experimental part
p. 4512 - 4514
(2009/11/30)
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- The Protecting-Directing Role of the Trityl Group in Syntheses of Pyrrole Derivatives: Efficient Preparations of 1-H-Pyrrole-3-carboxylic Acid and 3-Acyl, 3-Amino, and 3-Bromo-1-tritylpyrroles
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Trifluoroacetylation, formylation, and bromination of 1-tritylpyrrile occur regioselectively at the 3-position in high yields.Quantitative hydrolysis of the 3-trifluoroacetyl derivative and removal of the trityl group from the resulting acid with sodium in liquid ammonia furnishes a new, short, high-yielding synthessis of the simple 1-H-pyrrole-3-carboxylic acid. 1-Tritylpyrrole-3-carboxylic acid has been converted efficiently into 3-aminopyrroles via Curtius rearrangement of the derived azide: 3-amino-1-tritylpyrrole appears to exist in solution exclusively as its imino-Δ4-pyrroline tautomer. 1-H-3-t-Butyloxycarbonylaminopyrrole udergoes trifluoroacetylation regioselectively at the 2-position.Metallation of 1-tritylpyrrole with butyl-lithium in hexamethylphosphoric triamide gives rise to the unexpected products 9-phenylfluorene, 1-methoxycarbonylpyrrole and methyl triphenylmethylacetate (after work-up of the lithio-intermediates with carbon dioxide and methylation of the resulting acids).
- Chadwick, Derek J.,Hodgson, Simon T.
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