Cobalt-mediated cyclotrimerization and cycloisomerization reactions. Synthetic applications

This article reviews our contribution in the ®eld of the cobalt(I)-mediated cycliza-tions. The use of new unsaturated partners such as allenes extend the scope and the utility of the previously developed intramolecular [222] cyclotrimerization. The presence of chiral auxiliaries induced high level of diastereoselectivity in the enediynes cyclization. The discovery of cobalt(I) catalyzed ene-type reaction allows to propose an ef®cient route to the basic skeleton of tetracyclic diterpenes via a one-pot sequence of cyclizations: [ene-type]/ [222]/[42]. This cascade created six carbon-carbon bonds, four rings in a totally stereoselective manner. Finally, a new strategy to the taxoids is proposed.