The Claisen [3,3]-sigmatropic rearrangement uses either heat or a Lewis acid to convert an allyl vinyl ether to an γ,δ-unsaturated carbonyl compound via an early six-membered chair-like transition state. In acyclic systems, large groups adopt equatorial positions to minimize unfavorable 1,3-diaxial interactions. When a chair-like structure is disfavored, the reaction can proceed through a boat-like transition state.

• Allyl vinyl ethers are synthesized from (i) allylic alcohols by mercuric ion-catalyzed exchange with ethyl vinyl ether, (ii) allylic alcohols and vinyl ethers via acid catalyzed exchange, (iii) thermal elimination, (iv) Wittig olefination of allyl formates and carbonyl compounds, or (v) Tebbe olefination of unsaturated esters. ^[1]
• Allyl vinyl ethers don’t usually need to be isolated as their synthesis conditions tend to induce their rearrangement.^[1,2]
• Highly hindered (Lewis acid) catalysts, such as bis(phenoxy)methylaluminum can be used to control the E:Z ratio of the products. These catalysts tend to force the α substituent of the allyl group into an axial conformation, favoring the Z-isomer ^[2]
• Chirality is transferred to the rearrangement products if a chiral allylic alcohol is used to prepare the starting allyl vinyl ether; the stereoselectivity will depend on the diastereomeric chair like transition states. ^[1]

• Reagents: Lewis Acid
• Reactant: Allyl Vinyl Ether, Allyl Phenyl Ether, Substituted Allyl Phenyl Ether, or O-Allyl Acetoacetic Ester
• Product: γ,δ-Unsaturated Carbonyl Compound, Ortho-Allylphenol, Para-Allylphenol, or 2-Allyl Acetoacetic Ester Respectively
• Type of Reaction: [3,3]-Sigmatropic Rearrangment

Mechanism

Original Reaction Paper

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Related Reactions

Related Compounds