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.