Textbook Question
Propose mechanisms for the following reactions.
(d)
25. Condensation Chemistry
Robinson Annulation
1:32 minutesProblem 59b
Textbook Question
Show how you would use Robinson annulations to synthesize the following compounds. Work backward, remembering that the cyclohexenone is the new ring and that the double bond of the cyclohexenone is formed by the aldol with dehydration. Take apart the double bond, then see what structures the Michael donor and acceptor must have.
(b) 
Verified step by step guidance1
Step 1: Analyze the target molecule. The compound contains a cyclohexenone ring fused to another ring with a methyl group and a ketone functional group. The double bond in the cyclohexenone suggests it was formed via an aldol condensation followed by dehydration.
Step 2: Work backward to identify the Michael donor and acceptor. The cyclohexenone ring is formed by the Robinson annulation, which involves a Michael addition followed by an aldol condensation. Break the double bond in the cyclohexenone to determine the precursor structures.
Step 3: Identify the Michael acceptor. The cyclohexenone ring indicates that the Michael acceptor must be a molecule with an α,β-unsaturated ketone structure, such as methyl vinyl ketone (CH3C(O)CH=CH2).
Step 4: Identify the Michael donor. The fused ring system suggests that the Michael donor must be a diketone or a compound with an active methylene group capable of undergoing enolate formation. A likely candidate is 2-methyl-1,3-cyclohexanedione.
Step 5: Combine the Michael donor and acceptor. The Michael donor (2-methyl-1,3-cyclohexanedione) undergoes enolate formation and reacts with the Michael acceptor (methyl vinyl ketone) in a conjugate addition. This is followed by an intramolecular aldol condensation and dehydration to form the cyclohexenone ring in the target molecule.
Verified video answer for a similar problem:This video solution was recommended by our tutors as helpful for the problem above
Video duration:
1mWas this helpful?
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Robinson Annulation
Robinson annulation is a key synthetic method in organic chemistry that combines a Michael addition and an aldol condensation to form cyclic compounds. This reaction typically involves a Michael donor, such as an enolate, reacting with a Michael acceptor, followed by dehydration to create a double bond. Understanding this process is crucial for synthesizing complex ring structures, such as cyclohexenones, as indicated in the question.
Recommended video:
Guided course
04:12
Robinson Annulation
Aldol Condensation
Aldol condensation is a fundamental reaction in organic chemistry where aldehydes or ketones with alpha-hydrogens react to form β-hydroxy carbonyl compounds. This reaction involves the formation of an enolate ion, which then attacks another carbonyl compound. The subsequent dehydration of the β-hydroxy carbonyl leads to the formation of an α,β-unsaturated carbonyl compound, which is essential for the formation of the double bond in the cyclohexenone structure.
Recommended video:
Guided course
09:51Crossed Aldol
Michael Addition
Michael addition is a nucleophilic addition reaction where a nucleophile, typically an enolate ion, adds to an α,β-unsaturated carbonyl compound. This reaction is crucial in forming carbon-carbon bonds and is often the first step in the Robinson annulation process. Understanding the nature of the Michael donor and acceptor is vital for determining the structures needed to synthesize the desired compound, as seen in the question.
Recommended video:
Guided course
09:231,2 vs 1,4 Addition
Related Videos
Related Practice