Domanda del libro di testo
The Eschenmoser–Claisen reaction is a variant of the Claisen reaction studied in this chapter. Based on your answers to Assessments 22.53–22.55, predict a product of this reaction.
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Ch. 22 - Conjugated Systems 2: Pericyclic Reactions
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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TOC.tableOfContents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases/Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes 1: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes 2: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification 1: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification 2: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution 1: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution 2: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems 1: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems 2: Pericyclic Reactions54
- Ch. 23 - Benzene 1: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene 2: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Non è quello che usi tu?Cambia libro di testo
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Mullins 1st EditionCh. 22 - Conjugated Systems 2: Pericyclic ReactionsProblema 55
Mullins 1st EditionCh. 22 - Conjugated Systems 2: Pericyclic ReactionsProblema 55Capitolo 21, Problema 55
The Johnson–Claisen reaction is a variant of the Claisen reaction studied in this chapter. (a) Suggest a mechanism for the first step. (b) Predict the product (B) that would result from heating intermediate A.
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The Johnson–Claisen rearrangement involves the conversion of an allylic alcohol to an allylic ester. In the first step, the allylic alcohol reacts with the orthoester in the presence of a catalytic amount of acid (H2SO4) to form an intermediate hemiacetal.
The acid catalyzes the formation of the hemiacetal by protonating the orthoester, making it more electrophilic and susceptible to nucleophilic attack by the alcohol.
Once the hemiacetal is formed, it undergoes a rearrangement. The allylic group migrates to the oxygen atom, forming a new carbon-oxygen bond and resulting in the formation of an enol ether intermediate (A).
Upon heating, the enol ether intermediate (A) undergoes a [3,3]-sigmatropic rearrangement, which is characteristic of the Claisen rearrangement. This rearrangement involves the migration of the allylic group and the formation of a new carbon-carbon bond.
The final product (B) is an allylic ester, which is formed after the rearrangement and subsequent tautomerization of the enol ether intermediate.
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Johnson–Claisen Reaction
The Johnson–Claisen reaction is a variant of the Claisen rearrangement, involving the conversion of allylic alcohols into γ,δ-unsaturated carbonyl compounds. This reaction typically involves the use of an orthoester and an acid catalyst, leading to the formation of an intermediate enol ether, which rearranges to form the final product. Understanding this reaction is crucial for predicting the transformation of intermediate A to product B.
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02:10
Claisen-Schmidt Reaction
Mechanism of the Johnson–Claisen Reaction
The mechanism begins with the protonation of the orthoester by the acid catalyst, followed by nucleophilic attack by the allylic alcohol, leading to the formation of an enol ether intermediate. This intermediate undergoes a [3,3]-sigmatropic rearrangement, resulting in the formation of a γ,δ-unsaturated carbonyl compound. Recognizing these steps helps in suggesting the mechanism for the first step of the reaction.
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02:10Claisen-Schmidt Reaction
Sigmatropic Rearrangement
A sigmatropic rearrangement is a pericyclic reaction where a sigma bond adjacent to one or more pi systems migrates across the pi system. In the Johnson–Claisen reaction, a [3,3]-sigmatropic rearrangement occurs, where the enol ether intermediate rearranges to form a new carbon-carbon bond, leading to the formation of the final product. This concept is essential for predicting the structure of product B from intermediate A.
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03:20Nomenclature of Sigmatropic Shifts
Pratica correlata
Domanda del libro di testo
In Chapter 20, we studied the aldol reaction. Although not discussed at the time, this reaction is stereospecific, proceeding through the Zimmerman–Traxler transition state shown here.
(a) Show an arrow-pushing mechanism for this concerted reaction.
(b) Why is this a favorable mechanism?
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Domanda del libro di testo
Only after working Assessment 22.53, predict the product of the following reactions.
(b)
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Domanda del libro di testo
Only after working Assessment 22.53, predict the product of the following reactions.
(a)
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Domanda del libro di testo
The Ireland–Claisen reaction is a variant of the Claisen reaction studied in this chapter.
(a) Suggest a mechanism for the first step.
(b) Predict the product (B) that would result from heating intermediate A.
(c) Hydrolysis of B gives a carboxylic acid.
Suggest a mechanism for this reaction.
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Domanda del libro di testo
While not covered explicitly in this chapter, the ene reaction occurs similarly to the Diels–Alder reaction but replaces the electrons from one bond in the diene with the electrons in a C―H bond. Draw the mechanism for the following reaction. [Number the carbons and draw in the hydrogens of the product. And, of course, make a note of bonds formed and bonds broken.]
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