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Efficient and regioselective chromium(0)-catalyzed reaction of 2-substituted furans with diazo compounds: stereoselective synthesis of (2E,4Z)-2-aryl-hexadienedioic acid diesters
Authors:Norbert D Hahn  Karl Heinz Dötz
Institution:a Kekulé-Institut für Organische Chemie und Biochemie der Rheinischen Friedrich-Wilhelms-Universität, Gerhard-Domagk-Strasse 1, D-53121 Bonn, Germany
b Institut für Anorganische Chemie der Rheinischen Friedrich-Wilhelms-Universität, Gerhard-Domagk-Strasse 1, D-53121 Bonn, Germany
Abstract:Pentacarbonyl(η2-cis-cyclooctene)chromium(0) (1) catalyzes efficiently reactions of diazo compounds with electron-rich furans. The reaction of 2-methoxyfuran (2) with alkyl α-diazoarylacetate (3a-g) furnishes the (2E,4Z)-2-aryl-hexadienedioic acid diesters (4a-g) in excellent yields. These reactions are highly regioselective. The cyclopropanation intermediates formed from 1 and diazo compounds 3a-g always arise from a carbene addition to the less substituted Cdouble bond; length as m-dashC bond of 2. The resulting cyclopropanation product undergoes a ring opening reaction to form the corresponding (2E,4Z)-2-aryl-hexadienedioic acid diesters (4a-g). The pentacarbonylchromium(0)-catalyzed reactions of 2-alkylfuran (5a-b) with ethyl α-diazophenylacetate (3a) and 9-diazo-9H-fluorene (3h) produce the 1(E),3(E)-butadienes (6a-d) in very good yields.
Keywords:Diazo compounds  Cyclopropanation  Ring opening reaction  Chromium  Catalysis  Carbene complexes
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