Ht3-an-03 - Answers to Hour Examination#3 Chemistry 302X...

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Answers to Hour Examination #3, Chemistry 302X - 2003 1. OCH 3 O 1. LiAlH 4 (CH 3 ) 2 CH—Br CH 3 CH 2 CH 2 OH Li CrO 3 OCH 3 O H 3 O + (CH 3 ) 2 CH—Li H O H 2 O OH O (CH 3 ) 2 CH—Li OCH 3 O HOCH 3 (CH 3 ) 2 CH—Li NaOCH 3 H 2 O CH 3 I O H 3 O + H 2 O O ( 1 ) ( 2 ) pyridine full Eq. Claisen to the anion, alkylation, hydrolysis and decarboxylation ( 1 ) 2 Eq. ( 2 ) ( 1 ) 2. H 2 O 1. 2. H 2 O 3. KMnO 4 2. a. Chloronium ion formation is followed by opening by water at the more substituted position (as usual). Loss of chloride and deprotonation finishes it up. Cl 2 /H 2 O HOAc / 0 °C HOAc = CH 3 COOH, acetic acid O R Cl R Cl Cl H 2 O R Cl Cl HO R Cl
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b. But where does that bromide + chloride come from? Take a look at the ‘onium ion at the heart of the mechanism. There is an opportunity for NGP to form an equilibrating mixture of chloronium and bromonium ions. Cl 2 /H 2 O HOAc / 0 °C HOAc = CH 3 COOH, acetic acid R Br Cl H 2 O R Br O R Cl O R Br R Br Cl as in part (a) H 2 O (c) Basically an intramolecular Wittig reaction variation. The adjacent carbonyl group makes the use of the relatively weak base triethylamine possible.
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