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

Abstract

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.

Understanding the Mechanism of the Divergent Reactivity of Non-Heteroatom-Stabilized Chromium Carbene Complexes with Furfural Imines: Formation of Benzofurans and Azetines

“…Since their discovery in 1964, and especially during the last few decades, group 6 Fischer carbene complexes have demonstrated high versatility as a powerful synthetic tool. − However, non-heteroatom-stabilized carbene complexes, first reported by Casey in 1973, did not emerge as an alternative reagent until recently due to their low stability. Among them, non-heteroatom-stabilized alkynylcarbenes, smoothly in situ synthesized from the corresponding Fischer-type alkoxycarbenes, resulted in synthetically useful and experienced significant differences in terms of reactivity with their alkoxycarbene analogues.…”

Electronic Excitations in Fischer-Type Cr and W Aminocarbene Complexes: A Combined ab Initio and Experimental Study

“…In this way, the carbene ligand becomes the electrophilic center of the molecule with a partial positive charge, and the metal center gains partial negative charge and becomes the nucleophilic center of the molecule . Fischer aminocarbene complexes have found use in organic synthesis. − Typical synthetic routes include both thermal and photochemical redox reactions, usually with unsaturated hydrocarbons, leading to different types of heterocyclic compounds. − Fisher-type carbenes also exhibit promising catalytic properties , and can be used as electrochemical probes for biosensors …”