Alkene metathesis first-generation systems

Two RCM reactions were employed in a new and efficient route to a key chiral intermediate, isoquinuclidine 150, in the synthesis of alkaloid (-F)-catharanthine <06AG(I)5334>. The first RCM makes use of chiral enone 151, derived from L-serine, to generate a chiral dihydropyridinone 152. Intramolecular alkene metathesis of dialkenyl piperidine 153 generates 150, which represents the first example of the use of RCM in the generation of an azabicyclo[2.2.2]alkene system. 

The first generation of alkene metathesis catalysts was based on ill-defined systems constituted of transition-metal oxides supported on alumina or sihca or transition metal chlorides activated by organometallic activators (alkyl aluminum or tin compounds). These systems are ill-defined in that the structure of then-active sites remains unknown, even today. It should be noted that, although... 

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