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Draw a mechanism for the nucleophilic acyl substitution/addition reaction with LiAlH4. Why doesn't the reaction stop at the substitution reaction? What is the purpose of the protecting step?

Draw a mechanism for the nucleophilic acyl substitution/addition reaction with LiAlH4. Why doesn't the reaction stop at the substitution reaction? What is the purpose of the protecting step?

Chemistry
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
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Draw a mechanism for the nucleophilic acyl substitution/addition reaction with LiAlH4. Why doesn't the reaction stop at the substitution reaction? What is the purpose of the protecting step?

**Synthesis of a Silicon-Protected Alcohol** The reaction scheme demonstrates the steps required to convert the starting material, an enamine with an attached ester group, into a silicon-protected alcohol. Below is a detailed explanation of the reaction steps and the resulting chemical changes: **Reaction Conditions:** 1. **Reagents and Catalysts:** - **Step 1: Ph\(_2\)BuSi-Cl, Imidazole** - **Step 2: LiAlH\(_4\)** **Reaction Mechanism:** 1. **Step 1: Silylation** - The first step involves the protection of the hydroxyl group (OH) using Ph\(_2\)BuSi-Cl and imidazole. - The reagent Ph\(_2\)BuSi-Cl acts as silylating agent, which replaces the hydroxyl hydrogen atom (H) with the silyl group (OSiPh\(_2\)Bu). 2. **Step 2: Reduction** - The second step involves the reduction of the ester group using lithium aluminum hydride (LiAlH\(_4\)). - LiAlH\(_4\) is a reducing agent that reduces the ester (EtO\(_2\)C) to the corresponding alcohol (allyl-OH). **Structures and Changes:** - **Initial Structure:** - The initial structure contains an enamine with a hydroxyl group and an ester group. - The ester group is denoted as EtO\(_2\)C. - **Intermediate Structure:** - After Step 1, the hydroxyl group (OH) is replaced with a silyl group (OSiPh\(_2\)Bu). - **Final Structure:** - After Step 2, the ester group (EtO\(_2\)C) is reduced to an alcohol group (allyl-OH). **Outcomes:** - The final product features the silyl-protected hydroxyl group (OSiPh\(_2\)Bu) and an allyl-alcohol group created by the reduction. - The ratio 10:1 indicates the selectivity or yield of the desired product compared to any side products. **Summary:** - This reaction sequence demonstrates the conversion of an enamine with an ester group into a silyl-protected alcohol. The procedures include silylation
Transcribed Image Text:**Synthesis of a Silicon-Protected Alcohol** The reaction scheme demonstrates the steps required to convert the starting material, an enamine with an attached ester group, into a silicon-protected alcohol. Below is a detailed explanation of the reaction steps and the resulting chemical changes: **Reaction Conditions:** 1. **Reagents and Catalysts:** - **Step 1: Ph\(_2\)BuSi-Cl, Imidazole** - **Step 2: LiAlH\(_4\)** **Reaction Mechanism:** 1. **Step 1: Silylation** - The first step involves the protection of the hydroxyl group (OH) using Ph\(_2\)BuSi-Cl and imidazole. - The reagent Ph\(_2\)BuSi-Cl acts as silylating agent, which replaces the hydroxyl hydrogen atom (H) with the silyl group (OSiPh\(_2\)Bu). 2. **Step 2: Reduction** - The second step involves the reduction of the ester group using lithium aluminum hydride (LiAlH\(_4\)). - LiAlH\(_4\) is a reducing agent that reduces the ester (EtO\(_2\)C) to the corresponding alcohol (allyl-OH). **Structures and Changes:** - **Initial Structure:** - The initial structure contains an enamine with a hydroxyl group and an ester group. - The ester group is denoted as EtO\(_2\)C. - **Intermediate Structure:** - After Step 1, the hydroxyl group (OH) is replaced with a silyl group (OSiPh\(_2\)Bu). - **Final Structure:** - After Step 2, the ester group (EtO\(_2\)C) is reduced to an alcohol group (allyl-OH). **Outcomes:** - The final product features the silyl-protected hydroxyl group (OSiPh\(_2\)Bu) and an allyl-alcohol group created by the reduction. - The ratio 10:1 indicates the selectivity or yield of the desired product compared to any side products. **Summary:** - This reaction sequence demonstrates the conversion of an enamine with an ester group into a silyl-protected alcohol. The procedures include silylation
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