Enantioselective Synthesis of Guaianolides in the Osmitopsin Family by Domino Metathesis

Relay metathesis
enabled an improved access from (S)-citronellal to
the marine trisnorguaiane (−)-clavukerin
A. This hydroazulene was applied as an advantageously functionalized
building block for the asymmetric synthesis of the sesquiterpene lactone
osmitopsin and the proposed structure of 4,5-epoxyosmitopsin using
a chemo-, regio-, and diastereoselective diepoxide opening as the
key step.