Relay ring-closing metathesis strategies towards the synthesis of the ABC tricycle of Taxol

Two synthetic routes towards the ABC tricycle of Taxol are presented. They both involve a relay ring-closing metathesis reaction to make the central B ring in a convergent fashion. In the first approach, the extender arm is positioned on the A ring, and the C ring bears the relay tether in the second route. Metathesis precursors with diverse extender arms were efficiently synthesised; unfortunately, the crucial metathesis reactions failed to deliver the target compounds in all cases