One-step convergent synthesis of the steroid ring system via the coupling of gamma,delta-unsaturated Fischer carbene complexes with o-ethynylbenzaldehyde.
[reaction: see text]. Simultaneous and stereoselective construction of the steroid B and C rings is observed in a tandem process involving the coupling of o-ethynylbenzaldehyde with 2-alkenylcyclopentylcarbene-chromium complexes.