Stoichiometric π-complexes in asymmetric synthesis

When stoichiometric π-complexes are used in asymmetric synthesis, the metal centre can be brought into play in a series of reactions. In this way, the most efficient use is made of the metal/ligand system. In contrast, if asymmetric control is required at just a single synthetic step, the best way to proceed is to use a chiral catalyst system, so that only a small amount of the often expensive chiral auxiliary is then needed. However when catalytic control methods must operate in a series of separate reactions, the approach relies, at each step, on a new and highly selective recognition of an increasingly elaborate chiral substrate. After the first induction of asymmetry, subsequent asymmetric induction is diastereoselective, not enantioselective.