Fischer-Type Group 6 Carbene Complexes in the Synthesis of Optically Active Molecules

In the last decades Group 6 Fischer Carbene complexes have demonstrated their ability as an interesting tool in asymmetric synthesis. The use of this family of organometallic compounds permitted the access to a wide array of optically active and occasionally enantiopure molecules. In this sense, carbo- and heterocycles of different sizes -from three to eighth membered rings- along with open chain compound, have been synthesized. Additionally, the use of Fischer carbene complexes has, in some cases, dramatically simplified the access to some natural or biologically active molecules only accessible following other tedious methodologies. The synthesis of optically active molecules from Group 6 Fischer carbene complexes will be reviewed here from two points of view: from chiral and from achiral carbene complexes. Among the enantiopure carbene complexes a distinction between amino an alkoxycarbenes has been formulated. On the other hand, asymmetric synthesis with chiral alkoxycarbenes has been divided in three groups according to the position of the inductor of chirality: i) in the stabilizing group, ii) in the carbene ligand, iii) in the coordination sphere ligands. Finally, all the sections along this review have been subdivided according to the reaction type.