ChemInform Abstract: Rhodium‐Catalyzed Ring Expansion of Cyclopropanes to Seven‐Membered Rings by 1,5 C—C Bond Migration.

Abstract

Selective cleavage and subsequent elaboration of carbon–carbon σ bonds into complex molecules represents a fundamental challenge in chemistry. The C–C σ bonds of cyclopropanes are activated owing to ring strain, and the ring expansion of cyclopropanes is an attractive route to other ring systems because of the well-documented stereoselective methods for cyclopropanation.[1] Indeed, ring expansion of cyclopropanes to four- or five-membered rings by 1,2 or 1,3 migration is routinely practiced in organic synthesis [Eq. (1)].[2] In contrast, ring expansion of cyclopropanes to seven-membered rings by 1,5 C–C bond migration has not been developed as a general method, in spite of the prevalence of cycloheptane skeletons in natural products and pharmaceutical agents.[3] The 1,5 migration of a cyclopropane C–C bond has been mainly studied in bicyclo-[4.1.0]heptadienes and a few other conformationally constrained bicyclic compounds under thermal conditions.[4] In fact, it was reported that simple 1,3-dienylcyclopropanes underwent 1,3 C–C bond migration to form vinylcyclopentenes in the presence of Ni or Pd catalysts.[5]