Relay Cross Metathesis for the Iterative Ascent of the Terpenoids

We report the design and implementation of a relay cross

metathesis (ReXM) reaction for the ascent of the terpenoids in an iterative protocol. The method features the reaction of naturally occurring terpenoid building blocks – with preexisting trisubstituted olefins – which combine to construct a new trisubstituted olefin resulting in a five-carbon unit homologation. Subsequent functional group manipulation allows for the method to be repeated in an

iterative fashion. The method is used for the synthesis of a diterpenebenzoate macrolide of biogenetic relevance to the bromophycolide family of natural products.