A concise entry into the bicyclic cyclopropyl ketone derivatives 5 and 6 by way of a gold-catalyzed Ohloff–Rautenstrauch-type enyne cycloisomerization is described. The required substrates were prepared by an asymmetric addition of the branched allylzinc reagent 21 to the alkynyl aldehyde 17 mediated by the deprotonated bisoxazoline (BOX) ligand 22. Compounds 5 and 6 were then converted into a host of different members of the sesquisabina- and sesquithuja families of terpenoids, inter alia with the aid of iron-catalyzed cross-coupling reactions. As the relative and absolute configuration of 5 and 6 could be unambiguously established, the synthetic samples allowed the previously unknown stereostructures of various such terpenoids to be unraveled, including cis-sesquisabinene hydrate (33), 7-epi-sesquithujene (36), sesquisabinene B (37) and epoxy-sesquithujene (45). Moreover, the preparation of 6 also constitutes a formal total synthesis of cedrene (11) and cedrol (12).
If you can't find a tool you're looking for, please click the link at the top of the page to "Go to old article view". Alternatively, view our Knowledge Base articles for additional help. Your feedback is important to us, so please let us know if you have comments or ideas for improvement.