Question

What product would you expect from Claisen rearrangement of but-2-enyl phenyl ether?

Short answer

Ortho-allyl phenol is expected from the rearrangement.

Step-by-step solution

Understand the Claisen Rearrangement

The Claisen rearrangement is a [3,3]-sigmatropic rearrangement where an allyl vinyl ether is transformed into a γ,δ-unsaturated carbonyl compound. The rearrangement involves the migration of an allyl group from an oxygen atom to a carbon atom, creating a new carbon-carbon bond.

Identify the Structure of Reactant

But-2-enyl phenyl ether can be represented as C6H5-O-CH2-CH=CH-CH3. In this ether, the phenyl group is attached to the oxygen atom, while the but-2-enyl group (CH2-CH=CH-CH3) is also linked to the oxygen.

Determine the Rearrangement Pathway

During the Claisen rearrangement of this ether, the allyl group (CH2-CH=CH-CH3) will migrate from the oxygen atom to the ortho position of the benzene ring. This rearrangement maintains the double bond and results in the formation of a new C-C bond at the benzene ring.

Write the Product Structure

The expected product of the rearrangement is ortho-allyl phenol. This structure is C6H4(OH)-CH2-CH=CH-CH3, where the OH group is attached to the benzene ring, and the allyl group is adjacent to the hydroxyl group.

Key concepts

[3,3]-sigmatropic rearrangement

The [3,3]-sigmatropic rearrangement is a fascinating process in organic chemistry that features the movement of atoms within a molecule to form a new structure. This rearrangement is characterized by the shift of a group of atoms, typically through a concerted mechanism, where new bonds are formed and existing bonds are re-organized. What makes the [3,3]-sigmatropic rearrangement so intriguing is that it involves the movement of two groups of three atoms each within the molecule.
This specific type of rearrangement is important because it helps in forming new carbon-carbon bonds, which is crucial in forming more complex molecules. In the case of the Claisen rearrangement, an allyl group shifts from an oxygen atom to a carbon atom, allowing the molecule to transform very efficiently into a new structure without the need for additional reagents or catalysts.

• Typically involves a migration from position 3 to position 3 over a six-membered transition state that is cyclic.
• Keeps the total number of atoms in the system untouched, meaning no atoms are added or removed.
• Happens without breaking any covalent bonds during the shift, making it a reorganizational process.

Understanding this concept provides insight into how molecular structures can undergo significant changes, which is essential for designing synthesis pathways in organic chemistry.

allyl vinyl ether

Allyl vinyl ethers are chemical compounds that play a critical role in Claisen rearrangements. These ethers are compounds where an allyl group (usually a three-carbon chain with a double bond) is directly connected to a vinyl group via an oxygen atom, forming a bridge of atoms. The chemical structure can be envisioned as: R-O-CH=CH2, where R is the allyl component.
These ethers are uniquely suited to undergo [3,3]-sigmatropic rearrangements, like the Claisen rearrangement, due to their structure. The rearrangement process allows the allyl group to move, resulting in the formation of new products.

• The ether linkage begins with the breakage of the oxygen-to-allyl bond.
• The allylic double bond is preserved throughout the rearrangement process.
• This leads to a new carbon-carbon bond formation, transforming the ether into a more complex carbonyl compound.

Due to its structural stability and reactivity, allyl vinyl ethers are often employed in various synthesis reactions, making them highly valuable in creating complex molecular architectures efficiently.

γ,δ-unsaturated carbonyl compound

A γ,δ-unsaturated carbonyl compound is a key product formed from the Claisen rearrangement of allyl vinyl ethers. This class of compounds can be identified by its distinctive structural feature: a carbonyl group (C=O) that is flanked by unsaturated carbon atoms, meaning there are double bonds located at the gamma (γ) and delta (δ) positions relative to the carbonyl group.
This structure is important because it introduces regions of different electronic character and reactivity within the molecule. The multiple double bonds allow for further chemical transformations, which can lead to even more diverse organic molecules.

• The positioning of the double bonds relative to the carbonyl group enhances the molecule's stability and reactivity.
• These compounds can act as intermediates in forming complex organic structures.
• The presence of the carbonyl group typically increases the electrophilicity of the molecule, making it more reactive towards nucleophiles.

Understanding the formation and reactivity of γ,δ-unsaturated carbonyl compounds helps clarify why the Claisen rearrangement is such a valuable and widely used reaction in synthetic organic chemistry.