Benzylic Organometals via Reductive Metalation Procedures

Abstract

The review discusses two different reductive metalation approaches to the generation of benzylic organometals. In the first part, the scope of the generation of polar benzylic organometals by the reductive cleavage of carbon - heteroatom sigma bonds will be presented. Besides briefly showing the evolution of the technique, the review deals with recent achievements in the generation of benzylic derivatives of alkali metals by the reductive cleavage of carbon - halogen, carbon - oxygen, carbon - nitrogen and carbon - sulphur bonds. Significant synthetic applications of this procedure are described, showing that an appropriate choice of reaction conditions (solvent, temperature, alkali metal, employment of an electron shuttle) strongly affects the outcome of the cleavage reaction. In the second part, the application of the reductive metalation to carbon - carbon, carbon - oxygen and carbon - nitrogen double bonds is described, a procedure leading to the generation of vic-diorganometallic derivatives. Synthetic applications of these diorganometals are illustrated, underlining the possible application of 1,2-diarylsubstituted vic-dicarbanions as synthetic analogues of an activated form of an alkali metal that, however, function under homogeneous and mild reaction conditions. Keywords: Alkali metals, benzyllithium, benzylic organometals, electron transfer, functionalized organometals, reduction, reductive cleavage, reductive metalation, organometals, benzyl phenyl sulfides, 1, 2-dimethoxyethane (DME), Benzylic Chlorides, sodium naphthalenide, cumyl methyl ether, isocombretastatin