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Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Non è quello che usi tu?Cambia libro di testo
Capitolo 22, Problema 78a,b

Write equations showing the expected products of the following enamine alkylation and acylation reactions. Then give the final products expected after hydrolysis of the iminium salts.
(a) pyrrolidine enamine of pentan-3-one + allyl chloride
(b) pyrrolidine enamine of acetophenone + butanoyl chloride

Guida verificata passo dopo passo
1
Step 1: Understand the enamine reaction mechanism. Enamines are nucleophilic at the α-carbon due to resonance stabilization. They react with electrophiles such as alkyl halides (in alkylation) or acyl chlorides (in acylation) to form iminium salts.
Step 2: For part (a), identify the enamine structure. The pyrrolidine enamine of pentan-3-one is formed by the reaction of pyrrolidine with pentan-3-one. The enamine has a double bond between the α-carbon and the nitrogen, with the nitrogen bonded to the pyrrolidine ring.
Step 3: Perform the alkylation reaction for part (a). The nucleophilic α-carbon of the enamine attacks the electrophilic carbon of allyl chloride, displacing the chloride ion and forming a new C-C bond. This results in an iminium salt intermediate.
Step 4: For part (b), identify the enamine structure. The pyrrolidine enamine of acetophenone is formed by the reaction of pyrrolidine with acetophenone. The enamine has a double bond between the α-carbon and the nitrogen, with the nitrogen bonded to the pyrrolidine ring.
Step 5: Perform the acylation reaction for part (b). The nucleophilic α-carbon of the enamine attacks the electrophilic carbonyl carbon of butanoyl chloride, displacing the chloride ion and forming an iminium salt. Finally, hydrolyze the iminium salts from both reactions (a) and (b) with water to regenerate the corresponding ketones or aldehydes as the final products.

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Concetti chiave

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Enamines

Enamines are derivatives of imines formed by the reaction of secondary amines with carbonyl compounds. They contain a carbon-carbon double bond adjacent to a nitrogen atom, which makes them nucleophilic. This nucleophilicity allows enamines to react with electrophiles, such as alkyl halides or acyl chlorides, facilitating alkylation and acylation reactions.
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Enamine Mechanism

Iminium Salts

Iminium salts are positively charged intermediates formed during the reaction of enamines with electrophiles. When an enamine reacts with an electrophile, it forms an iminium salt, which can be hydrolyzed to yield the final product. Understanding the formation and hydrolysis of iminium salts is crucial for predicting the final products of the reactions in question.
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General Reaction

Hydrolysis

Hydrolysis is a chemical reaction involving the breakdown of a compound by water. In the context of iminium salts, hydrolysis leads to the regeneration of the original carbonyl compound and the corresponding amine. This step is essential for determining the final products after the alkylation or acylation of the enamine, as it reveals the transformation of the iminium salt back into stable products.
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Percorso guidato
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Hydrolysis of Thioesters Concept 2