week 3 - 4 - anno

week 3 - 4 - anno - Chemistry S-20ab Chemistry E-2a:...

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Addition of Water to Alkynes: Enol Formation The following reaction produces an unstable intermediate known as an enol (alk ene + alcoh ol = enol) . Draw a complete curved-arrow mechanism for this reaction up to the formation of the enol. C C H Hg 2+ , H + , H 2 O OH enol (unstable) Reading : Section 14.5 Chemistry S-20ab Week 3 177
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Addition of Water to Alkynes: Enol Hydrolysis The enol is not the final product of the reaction of an alkyne with water. The enol reacts rapidly with the aqueous acid to form a carbonyl compound: in this case, a ketone . Provide a complete curved-arrow mechanism for the following reaction: OH enol (unstable) H + , H 2 O O ketone Show the complete synthetic transformation from an alkyne to a ketone : Reading : Section 14.5 Chemistry S-20ab Week 3 178
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Hydroboration/Oxidation of Alkynes: Enol Formation The following reaction produces an unstable intermediate known as an enol (alk ene + alcoh ol = enol) . Draw a complete curved-arrow mechanism for this reaction up to the formation of the enol. You should also explain why the alkene geometry is trans (that is, you should explain the stereochemistry !) C C H enol (unstable) 1. R 2 BH (R = bulky alkyl group) 2. H 2 O 2 , OH OH Reading : Section 14.5 Chemistry S-20ab Week 3 179
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Hydroboration/Oxidation of Alkynes: Enol Hydrolysis The enol is not the final product of hydroboration/oxidation of an alkyne. The enol reacts rapidly with the aqueous base (in the oxidation step) to form a carbonyl compound: in this case, an aldehyde . Provide a complete curved-arrow mechanism for the following reaction: enol (unstable) OH , H 2 O aldehyde OH H O Show the complete synthetic transformation from an alkyne to an aldehyde : Reading : Section 14.5 Chemistry S-20ab Week 3 180
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This note was uploaded on 07/21/2010 for the course CHEM S20ab taught by Professor Mccarty during the Summer '10 term at Harvard.

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week 3 - 4 - anno - Chemistry S-20ab Chemistry E-2a:...

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