[reaction: see text] A synthesis of the tricyclic [5-7-6] skeleton of guanacastepene A is described. The six-membered ring of guanacastepene A was constructed by a Diels-Alder reaction. After several functional group transformations, it was coupled to beta-iodocyclopentenone. Lithium dimethylcuprate conjugate addition followed by an intramolecular Mukaiyama aldol reaction furnished the desired [5-7-6] tricyclic ring system.
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