Ruthenium-catalysed carbenoid cyclopropanation reactions with diazo compounds.

The transition-metal catalysed cyclopropanation of olefinic bonds using diazo compounds as a carbene source is among the best developed and most useful transformations available to the synthetic organic chemist. Nevertheless, the quest for new catalyst/ligand systems continues in order to further extend the scope of this method and to identify more economical catalytic systems. In this tutorial review, several different ruthenium complexes are presented which have recently emerged as suitable catalysts for carbenoid cyclopropanation. For the model reaction--cyclopropanation of styrene(s) with diazoacetates--and also for some intramolecular cyclopropanation reactions highly remarkable results in terms of catalyst efficiency, product yields, dia- and enantioselectivity have been reported.