Rhodium(II)-Catalyzed Isomerization of Cyclopropenylmethyl Esters into (Acyloxymethylene)cyclopropanes

In the presence of a rhodium(II) catalyst, 3,3-disubstituted cyclopropenylmethyl esters that possess an electron-rich or neutral aromatic group undergo isomerization into (acyloxymethylene)cyclopropanes. This transformation, which proceeds with inversion of configuration at the stereogenic center, complements the previously disclosed rearrangement reactions of cyclopropenylmethyl esters. The products arising from this new rhodium-catalyzed rearrangement contain an enol ester group that can be subsequently functionalized to access stereodefined arylcyclopropanes. In the presence of [Rh₂(OAc)₄], 3,3-disubstituted cyclopropenylmethyl esters that possess an electron-rich or neutral aromatic group undergo isomerization into (acyloxymethylene)cyclopropanes (see scheme). This transformation complements previously disclosed rearrangements of cyclopropenylmethyl esters. The products arising from this rearrangement contain an enol ester, which can be subsequently functionalized to access stereodefined arylcyclopropanes.