LAB 6 Materials

LAB 6 Materials - CHAPTER 6: CYCLOADDITION REACTIONS, 6.1....

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1 CHAPTER 6: CYCLOADDITION REACTIONS, 6.1. BACKGROUND, 6.1.1. Diels-Alder Reaction This reaction was developed by Otto Diels and Kurt Alder, two German scientists, in 1928. The reaction is so powerful for the preparation of polycyclic compounds that they were awarded the Nobel Prize in Chemistry in 1950. This is a [4+2]-cycloaddition reaction between a conjugated diene and a dienophile (an alkene or alkyne), and involves the 4 π -electrons of the diene and 2 π -electrons of the dienophile to form an unsaturated six-membered ring. The driving force of the reaction is the formation of new σ -bonds, which are energetically more stable than the π -bonds. The Diels-Alder reaction is a concerted process and is stereospecific with respect to both the diene and the dienophile (Figure 6.1). The addition is syn on both components. This means a cis- dienophile gives cis- substituents in the product and a trans- dienophile gives trans- substituents in the product. If the diene substituents have the same stereochemistry (both E), then both end up on the same face of the product. If the diene substituents have opposite stereochemistry (one E and one Z), then they end up on opposite faces of the product. Cyclic dienes can give stereoisomeric products depending on whether the dienophile lies under or away from the diene in the transition state. The endo product is usually the major product (due to kinetic control). CO 2 Et CO 2 Et CO 2 Et CO 2 Et CO 2 Et EtO 2 C CO 2 Et CO 2 Et CO 2 Et CO 2 Et CO 2 Et CO 2 Et CO 2 Et CO 2 Et CO 2 Et CO 2 Et O O O O O O O O O O O O H H H H O O O endo product (major) exo product (minor) Mechanism: Figure 6.1. The stereochemistry of Diels-Alder adducts.
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2 6.2. CYCLOADDITION WITH ANTHRACENE, + Ethylene glycol Anthracene N-Methylmaleimide 170 o C / 1 h N O O CH 3 N O O H H CH 3 DA Adduct 6.2.1. Reaction Stoichiometry Parameters Anthracene N-Methylmaleimide Ethylene glycol DA Adduct Formula weight 178.23 111.10 289.33 Required mol ratio 1 1.1 Suggested amount* ~0.5000 g 0.3428 g* 10 mL mmol 2.81 3.09 2.81 Theoretical yield 0.8117 g* *The amount of N-methylmaleimide should be recalculated based on the exact amount (4 decimals) of anthracene weighed, around 0.5 g. Theoretical yield will be altered accordingly. 6.2.2. Materials 1. Anthracene (~0.6 g) 2. N-Methylmaleimide (~0.4 g) 3. Ethylene glycol (15 mL) 4. Distilled water (200 mL) 5. Ethanol (5 mL) 6. Anhydrous CaCl 2 (~10 g) for guard tube 6.2.3. Glassware and Accessories 1. 25 mL 19 joint 2-neck flask (1) 2. Thermometer inlet assembly (1) 3. Reflux condenser (1) 4. Heating mantle or sand bath (1)
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This note was uploaded on 03/03/2010 for the course CHEM 240 taught by Professor Mandal during the Spring '10 term at Illinois Tech.

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LAB 6 Materials - CHAPTER 6: CYCLOADDITION REACTIONS, 6.1....

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