discovered in 1912 by rainer ludwig claisen, the claisen rearrangement is the first recorded example of a [3,3]-sigmatropic rearrangement. this rearrangement is a useful carbon-carbon bond-forming reaction. an example of claisen rearrangement is the [3,3] rearrangement of an allyl vinyl ether, which upon heating yields a γ,δ-unsaturated carbonyl. the formation of a carbonyl group makes this reaction, unlike other sigmatropic rearrangements, inherently irreversible.