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[reaction: see text] A 12-step synthesis of 26, the functionalized hydroazulenone ring of guanacastepene (1), has been completed using the EtAlCl(2)-initiated cyclization of gamma,delta-unsaturated ketone 13 to construct 2,2,3-trisubstituted cyclopentanone 14, the palladium-catalyzed coupling of vinylmagnesium bromide with enol triflate 17 to prepare triene 21, and olefin metathesis of triene 21 to form the key hydroazulene 20.
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