Enantioselective total synthesis of the potent antitumor agent (-)-mucocin using a temporary silicon-tethered ring-closing metathesis cross-coupling reaction.

The enantioselective total synthesis of the annonaceous acetogenin (-)-mucocin (1) was accomplished using a triply convergent 12-step sequence (longest linear sequence) in 13.6% overall yield. This represents the first application of the temporary silicon-tethered (TST) ring-closing metathesis (RCM) cross-coupling reaction and the enantioselective alkyne/aldehyde addition to the synthesis of a complex annonaceous acetogenin. Moreover, all three fragments required for the coupling reactions are conveniently prepared in 5-6 steps from two readily available enantiomerically enriched epoxides. Finally, this synthesis stimulated the development of a new approach for the construction of 3-hydroxy-2,6-disubstituted tetrahydropyrans, using the bismuth tribromide-mediated reductive etherification reaction, which represents a motif that is prevalent in a wide range of pharmacologically significant natural products.

Novel P,N-bidentate phosphite ligands in asymmetric catalysis.

Results achieved by the authors in the synthesis of chiral P,N-phosphite ligands are summarized. Three groups of new chiral P,N-phosphites are discussed, namely, ligands derived from 1,1'-bi-2-naphthol, ligands possessing an acyclic phosphorus center, and P*-chiral ligands derived from (S)-2-anilinomethylpyrrolidine. An overview of complexation of the ligands with Rh(I) and Pd(II) precursors is given. Accessibility and stability of chiral phosphite ligands possessing acyclic phosphorus was analyzed for the first time along with their efficiency in terms of stereoselectivity. The title ligands are shown to be highly efficient in the Pd-catalyzed allylic alkylation (up to 85% ee) and, especially, allylic sulfonylation (up to 97% ee) reactions in certain cases outperformed all known catalytic systems.