Week_6.4_PurpleBook_Answers

Week_6.4_PurpleBook_Answers - 165 Beckmann, Curtius, and...

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O Cl O N N O N O OH N N O C N NH OCH 3 O N OH 2 N N OH 2 H N O Br Br NH O Beckmann, Curtius, and Hofmann Rearrangements 1. Provide the intermediates and products for the following transformations, and write a curved-arrow mechanism for the crucial rearrangement step. N O Br O C Beckmann N Br 2 ,OH NH O O protonation and deprotonation NH 2 proton transfers carbamic acid undergoes spontaneous decarbox. Curtius Hofmann N O Br H NH 2 OH NaN 3 NaOCH 3 :OCH 3 H + :OH 2 :OH :OH This isocyanate can be isolated and reacted further with a nucleophile (such as the alkoxide here.) This isocyanate cannot be isolated as it is formed in the presence of a good nucleophile (the aqueous base.) H H H 3 O + NH OH O Week 6 165
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H O N H H 3 C CH 3 H O N HN O N O CH 3 CH 3 Ph H OH N H H 3 C CH 3 H HO NMe 2 H H H 2 O NMe 2 H OH H H NMe 2 H OH H OH N CH 3 CH 3 The Mannich Reaction Ph O 1. Provide a curved-arrow mechanism for the following transformation. H + pH 5 2. Show how a Mannich reaction can be used to complete the following synthetic transformation. ??? N O Ph enol iminium proton transfer N HO –H + Ph pH 5 , imine formation mechanism (same as above) N HO form enol (same as above) Ph –H + H + :OH 2 Week 6 166
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Aromatic Heterocycles N N CH 3 CH 3 N N CH 3 CH 3 1. a) Consider the compound 2-dimethylaminopyridine, shown below. In the box, draw the structure of the species that would result from single protonation of 2-dimethylaminopyridine: b) In the box below, draw the structure of the primary product which should result if 2- dimethylaminopyridine is subjected to electrophilic aromatic substitution with the general electrophile " E + ". 1equ iv .H + E + (electrophilic aromatic substitution) c) In the space below, show all the significant resonance structures for the positively charged, non- aromatic intermediate which would be formed during the electrophilic aromatic substitution reaction in part (b) above. H N N CH 3 CH 3 + N N CH 3 CH 3 E N N CH 3 CH 3 E H N N CH 3 CH 3 E H N N CH 3 CH 3 E H N N CH 3 CH 3 E H
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More Aromatic Heterocycles 1. Consider the bromination of pyrrole: N N a) Provide a complete curved-arrow mechanism for this transformation. Br
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Week_6.4_PurpleBook_Answers - 165 Beckmann, Curtius, and...

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