A [1,5] sigmatropic rearrangement is a type of pericyclic reaction in organic chemistry where a substituent migrates from one position to another position five atoms away, resulting in the formation of a new carbon-carbon bond.
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The [1,5] sigmatropic rearrangement involves the migration of a substituent from one position to another position five atoms away, forming a new carbon-carbon bond.
These rearrangements are classified as suprafacial-suprafacial, meaning the migrating group retains its stereochemistry during the reaction.
The transition state of a [1,5] sigmatropic rearrangement is cyclic and can be described using frontier molecular orbital theory.
Examples of [1,5] sigmatropic rearrangements include the Cope rearrangement and the Claisen rearrangement.
The stereochemistry of the starting material is retained in the product of a [1,5] sigmatropic rearrangement.
Review Questions
Describe the general mechanism of a [1,5] sigmatropic rearrangement.
In a [1,5] sigmatropic rearrangement, a substituent migrates from one position to another position five atoms away, resulting in the formation of a new carbon-carbon bond. The transition state of this reaction is cyclic, and the process is classified as a suprafacial-suprafacial pericyclic reaction, meaning the stereochemistry of the migrating group is retained in the product. The mechanism can be explained using frontier molecular orbital theory, which predicts the feasibility and stereochemistry of the rearrangement.
Explain the role of frontier molecular orbital theory in understanding [1,5] sigmatropic rearrangements.
Frontier molecular orbital theory is a crucial tool for understanding the mechanism and predicting the feasibility of [1,5] sigmatropic rearrangements. This theory focuses on the interactions between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the reactants. In the case of [1,5] sigmatropic rearrangements, the cyclic transition state can be analyzed using frontier molecular orbital theory to determine the most favorable orbital interactions and, consequently, the stereochemistry of the product.
Evaluate the importance of [1,5] sigmatropic rearrangements in organic synthesis and their applications.
$$[1,5] \ \text{sigmatropic rearrangements are important in organic synthesis because they allow for the formation of new carbon-carbon bonds in a stereospecific manner}. \ \text{These rearrangements are widely used in the synthesis of complex organic molecules, as they provide a way to efficiently construct}$$
$$\text{new ring systems and introduce functional groups at specific positions. Some key applications include the Cope rearrangement in the synthesis of natural products and the Claisen rearrangement in the preparation of allyl vinyl ethers. Understanding the mechanism and stereochemistry of [1,5] sigmatropic rearrangements is crucial for designing efficient synthetic routes and predicting the outcome of these transformations.}$$
Related terms
Pericyclic Reaction: A pericyclic reaction is a type of organic reaction that involves the cyclic movement of electrons around a transition state.
Sigmatropic Shift: A sigmatropic shift is a type of pericyclic reaction where a substituent migrates from one position to another within the same molecule.