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4. Aldehydes and ketones can be "protected" as acetals and ketals. Complete the following outlined reactions, showing how the protection is accomplished, and what results after deprotection. Br „MgBr 1) Br 2) H3O* deprotection here

4. Aldehydes and ketones can be "protected" as acetals and ketals. Complete the following outlined reactions, showing how the protection is accomplished, and what results after deprotection. Br „MgBr 1) Br 2) H3O* deprotection here

Organic Chemistry
Organic Chemistry
8th Edition
ISBN:9781305580350
Author:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. Foote
Publisher:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. Foote
Chapter11: Ethers, Epoxides, And Sulfides
Section: Chapter Questions
Problem 11.41P: Aldehydes and ketones react with one molecule of an alcohol to form compounds called hemiacetals, in...
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### Protection of Aldehydes and Ketones as Acetals and Ketals Aldehydes and ketones can be "protected" as acetals and ketals. Complete the following outlined reactions, showing how the protection is accomplished, and what results after deprotection. 1. **Starting material:** A benzene ring with a bromomethyl (—CH₂Br) substituent and an aldehyde (—CHO) group attached directly to the ring. 2. **Formation of Acetal:** - The carbonyl group (aldehyde) reacts with a diol (ethylene glycol, C₂H₄(OH)₂) to form a cyclic acetal (with an oxygens in a five-membered ring). - This reaction effectively "protects" the carbonyl group by transforming it into an acetal, which is more stable under basic conditions and prevents it from undergoing unwanted side reactions. 3. **Grignard Reaction:** - The bromo substituent reacts with magnesium (Mg) to form a Grignard reagent (R—MgBr), where R is the benzene ring attached to the oxygens of the acetal. 4. **Reaction with Aldehyde/Ketone:** - The Grignard reagent reacts with a carbonyl compound (another aldehyde or ketone group) leading to the formation of a new carbon-carbon bond. 5. **Deprotection:** - The cyclic acetal is then hydrolyzed (broken down) back to the original carbonyl group using aqueous acid (H₃O⁺), completing the deprotection step, revealing the original functional group. ### Diagram Explanation - The initial chemical structure consists of a benzene ring with a bromomethyl and an aldehyde group. - The aldehyde is protected by forming a cyclic acetal with ethylene glycol. - The bromine is replaced by a Grignard reagent (MgBr). - The Grignard reagent reacts with a new carbonyl compound to form an intermediate. - Finally, the cyclic acetal is hydrolyzed to restore the aldehyde group, completing the deprotection. Complete the reactions to show the final product after deprotection, illustrating the transformation and the utility of protection groups in synthetic organic chemistry.
Transcribed Image Text:### Protection of Aldehydes and Ketones as Acetals and Ketals Aldehydes and ketones can be "protected" as acetals and ketals. Complete the following outlined reactions, showing how the protection is accomplished, and what results after deprotection. 1. **Starting material:** A benzene ring with a bromomethyl (—CH₂Br) substituent and an aldehyde (—CHO) group attached directly to the ring. 2. **Formation of Acetal:** - The carbonyl group (aldehyde) reacts with a diol (ethylene glycol, C₂H₄(OH)₂) to form a cyclic acetal (with an oxygens in a five-membered ring). - This reaction effectively "protects" the carbonyl group by transforming it into an acetal, which is more stable under basic conditions and prevents it from undergoing unwanted side reactions. 3. **Grignard Reaction:** - The bromo substituent reacts with magnesium (Mg) to form a Grignard reagent (R—MgBr), where R is the benzene ring attached to the oxygens of the acetal. 4. **Reaction with Aldehyde/Ketone:** - The Grignard reagent reacts with a carbonyl compound (another aldehyde or ketone group) leading to the formation of a new carbon-carbon bond. 5. **Deprotection:** - The cyclic acetal is then hydrolyzed (broken down) back to the original carbonyl group using aqueous acid (H₃O⁺), completing the deprotection step, revealing the original functional group. ### Diagram Explanation - The initial chemical structure consists of a benzene ring with a bromomethyl and an aldehyde group. - The aldehyde is protected by forming a cyclic acetal with ethylene glycol. - The bromine is replaced by a Grignard reagent (MgBr). - The Grignard reagent reacts with a new carbonyl compound to form an intermediate. - Finally, the cyclic acetal is hydrolyzed to restore the aldehyde group, completing the deprotection. Complete the reactions to show the final product after deprotection, illustrating the transformation and the utility of protection groups in synthetic organic chemistry.
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