Enantioselective synthesis of the originally proposed usneoidone structure:: Evidence for a structural revision

The enantioselective synthesis of the initially proposed structure of usneoidone has been completed according to a convergent strategy in which the key steps were an enantioselective Michael addition involving chiral imines to set up the C12 quaternary center, and the final assembly of the chiral pyran moiety with the aromatic subunit through a cyanohyd-rin anion alkylation step. The obtained product displays spectroscopic data that significantly differ from the reported values. A putative revised structure in which the pyran ring is opened is proposed for usneoidones. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).