An Enantioselective Central-Axial-Central Chiral Element Transfer Process Leading to a Concise Synthesis of (+)-Sterpurene: Intramolecular Diels-Alder Reactions of Vinylallene Sulfoxides

Article abstract of DOI:10.1021/ja00192a033

The intramolecular Diels-Alder (IMDA) reaction of vinylallene sulfoxide 19 as the diene component occurs in a rapid and stereoselective manner at room temperature to give tricyclic 20 in good yield.Sulfoxide 19 cyclizes ca. 140 times faster than the corresponding hydrocarbon 15a.It was also shown that gem-dimethyl substitution on the tether linking the vinylallene and vinyl group accelerates the rate of cyclization by only a factor of ca. 2.6.Treatment of enantiomerically enriched diene propargyl alcohol 6 with benzenesulfenyl chloride gave vinylallene sulfoxide 4which cyclized in a highly enantio- and diastereoselective fashion to afford optically active tricyclic sulfoxide 5.Sulfoxide 5 was converted in two steps to the novel sesquiterpene fungal metabolite (+)-sterpurene, thus establishing its absolute configuration.By use of 2D NMR techniques, most of the proton and carbon signals in the (1)H and (13)C NMR spectra of sterpurene (8) and the precursor diene 33 were assigned.