Stereoselective, oxidative C-C bond coupling of naphthopyran induced by DDQ: Stereocontrolled total synthesis of deoxyfrenolicin

A formal total synthesis of pyranonaphthoquinone natural product deoxyfreno licin 1 is described. The key step in the synthesis involves the use of ste reoselective 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)-induced C-C bo nd coupling of the naphthopyran 10 with allyltriphenyltin to give exclusive ly 1,3 trans naphthopyran derivative 23, The naphthopyran 10 was obtained v ia oxa-Pictet-Spengler cyclization of substituted naphthalene 22, which was derived by regioselective benzannulation of chromium carbene complex 12 wi th acetylene 18, This newly developed synthetic route employing a tandem be nzannulation/oxa-Pictet-Spengler cyclization/DDQ-induced coupling strategy should also be applicable to the synthesis of other pyranonaphthoquinone na tural products such as kalafungin 4 and nanaomycin 5.