2311 lec 6 - The Diels-Alder Reaction Preparation The Alder...

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Unformatted text preview: The Diels-Alder Reaction: Preparation The Alder of 1,2,3,4-Tetraphenylnaphthalene of Review of the Diels-Alder reaction Review Essay – Diels-Alder Reaction and Insecticides Essay Experiment – Experiment – – – – – – Our Dienophile – BENZYNE Our Our Diene – Tetraphenylcyclopentadienone Our “Syringe Pump” Method Solvent Pair Crystallization 1H NMR 1H Melting Points! Allotropic! Classic Diels-Alder Reaction Classic EWG + heat EWG No reagents needed (often no solvent) No Concerted mechanism Concerted Often No by-products Often Efficiently forms 6-membered ring with substituents of Efficiently predictable regio and stereochemistry Pivitol in historical synthesis of steroids and insecticides Pivitol Pavia Essay – Diels-Alder Reaction Alder and Insecticides and Our Experiment – Formation in situ Formation of the Dienophile BENZYNE of CO2H NH2 CO2 N N -CO2 -N2 BENZYNE ONO DME, heat Mechanism Mechanism Key Steps – Formation of Diazonium Salt and Key Formation Diazonium Salt loss of CO2 and N2 loss CO2H NH2 CO2 NH3 ONO proton transfer CO2 O H N H N O H R-OH O O N O N -CO2 -N2 heat R-OH CO2 NH2 H + O ON -HOR CO2 N N OH H R-OH CO2 ROH O C CO2 N H N CO2 NO N HH H NO H N -H2O NN Loss of Gases Loss O C O O N O N heat NN Cyclic intermediate Diazonium Salt + N2 + CO2 Strained, highly reactive Reaction with Diene Reaction O Ph Ph O Ph Ph - Ph + heat Ph Ph Ph heat -CO Ph Ph Ph Ph concerted, 6 e Watch for disappearance of purple diene color Watch Spontaneous loss of CO to form aromatic system! Spontaneous Stable, symmetrical product Stable, Procedure Procedure Need to add reagents slowly to prevent formation Need of by-products. Research lab – syringe pumps products. syringe would be used. would Watch for disappearance of purple color Watch Add both isoamyl nitrite and anthranilic acid if Add reaction doesn’t go. Filter product. Filter Recrystallize from EtOH/water Recrystallize Take melting point from solvent crystallization then Take “molten” melting point Allotropes – same pure compound different Allotropes different melting points due to different crystal packing. NMR and MM2 NMR Ph Ph Ph Ph Ha Ha Hb Hb ...
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