Ruthenium-Catalyzed Cascade Reactions in Total Synthesis

3 RUTHENIUM-CATALYZED CASCADE REACTIONS IN TOTAL SYNTHESIS 

In the past decade, chemists have become more and more interested in ruthenium catalysts for organic synthesis, since ruthenium catalysts are able to perform specific new reactions with a large number of applications [54]. A variety of cascade reactions and sequential catalytic transformations have been developed based on this powerful catalyst system, which can promote several different types of reactions. 

One of the most important cascade sequences by rhodium catalysis is the tandem RCM/cross-metathesis (CM) sequence, which includes two metathesis processes. The first process builds up the cyclic framework via an RCM process and then functionalizes the lateral chain of the intermediate vinyl intermediate 5, thanks to a subsequent CCM reaction with a conveniently chosen alkene. 

Kempene-2 156, kempene-1 157 and 3-ept-kempene-l 158 are diterpenes with a kempane skeleton isolated from the defense secretion of termite soldiers of the 

SCHEME 7.32 Tandem metathesis reaction used in the total synthesis of alkaloid natural products. 

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Ruthenium-catalyzed cascade reactions in total synthesis... 

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