Ruthenium Indenylidene Complexes in Alkene Metathesis

The first efficient application of a well-defined ruthenium indenylidene complex in metathesis was described in 1999 by Frirstner for the total synthesis of a cyclic prodigiosin derivative, a potential lead compound for the development of immunosuppressive agents. The RCM using the ruthenium indenylidene complex DC (10 mol%) as precatalyst leads to the transformation of the N-protonated diene into the desired macrocycle in 65% yield (Equation 8.8) [43]. 

Actually, applications of indenylidene-ruthenium complexes for alkene metathesis were reported before, at a time when the action mode of their ruthenium allenylidene precursors was not known. These complexes catalyzed a variety of RCM reactions of dienes and enynes [31, 32, 47] (see Section 8.2.2). 

The same catalyst IX was used in the RCM of a functional diene to give, in 87% yield, a tetrahydroazepine derivative which is a precursor in the synthesis of the metabolite (-)-Balanol (Equation 8.9) [44]. 

The ruthenium indenylidene IX catalyzed the ring dosing metathesis of a homoallyl ether diene to give a bicydic compound, which is an intermediate for the synthesis of different marine natural products (Equation 8.10) [63]. 

During the same period, Nolan showed also that indenylidene complexes are active catalyst precursors in the RCM of dienes. The reactions were performed on the NMR scale and moderate to good yields were obtained for diethyl diallylmalonate. 

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