Donor-acceptor cyclopropanes as three-carbon components in a [4+3] cycloaddition reaction with 1,3-diphenylisobenzofuran

Article abstract of DOI:10.1002/anie.200704438

(Chemical Equation Presented) Dienophiles with a difference: 2-Aryl 1,1-bis(alkoxycarbonyl) cyclopropanes undergo the title reaction under the catalysis of ytterbium triflate (Yb(OTf)₃) in excellent yield (see scheme). Under mild reaction conditions, the major product is the less stable exo isomer. At higher temperatures, the endo isomer is obtained exclusively, as the exo cycloadduct decomposes through cycloreversion.