Abstract
Abstract: A catalytic and highly stereoselective synthesis of a com-mon building block for the marine natural product puupehedione ( 1 )and its biologically more active 8-epimer is described. Our ap-proach features a copper-catalyzed allylic substitution reaction ofepoxyfarnesyl acetate and a diastereoselective titanocene-catalyzedepoxypolyene cyclization via radicals. The formal syntheses of 1 and 2 are completed by highly diastereoselective ring closures to therequired benzodihydropyran units. Key words: catalysis, cuprates, epoxypolyene cyclization, naturalproducts Many biologically active compounds, some of them ofmarine origin, are composed of sesquiterpene units linkedto phenolic structures. 1 Prominent examples includepuupehedione ( 1 ), 2a its 8-epimer 2 , 2b and numerousderivatives with varying oxidation patterns on the arenemoiety. 3 They possess important biological properties,e.g. antitumor, 4 antiviral, 5 and antibiotic activities. 6 Over the last years the radical chemistry originating fromtitanocene-catalyzed epoxide opening has attracted a greatdeal of attention.
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