LAUSR

The retro-Claisen [3,3]-sigmatropic rearrangement of ,-enoyl compounds allows to form a CO bond while breaking a CC bond in a concerted process. It is rarely observed with acyclic substrates. However, when the alkene and carbonyl groups are tethered by a cyclopropane, this rearrangement results in ring expansion, to form a 2,5-dihydrooxepine whose stability entirely depends on the substitution pattern. After its discovery in the 1960's, applications have resulted in the development of original methodologies and total synthesis, mainly spread over the last 20 years. This minireview aims at describing the historical discovery, the study of substrate reactivity, and the recent applications of this reaction, discussing the formation of stable, metastable or elusive 2,5-dihydrooxepines.