The possibility of achieving convergentsyntheses with elaborate carbenes is illustrated by the isobutenylalkynylcarbene II (R Br). By reaction with 3-cyclohexen-1-one, the endo cyclopropanic adduct IIIa is formed as a major product. Metalation with MeLi, followed by reaction with MeI, proceeds with inversion of configuration (-> sesquicarene skeleton, XI), or, after protection of the ketofunction