A series of C-silylated enynols, e.g. 6-methyl-l-trimethylsilyl-hept-5-en-l-yn-4-ol ( rac - A ) was prepared and submitted to N -iodosuccinimide mediated iodoalkoxylation of tri- O -acetylglycal Thanks to the presence of the silyl group the resulting diastereomeric glycosides (S) A 1 and (R) A 1 were readily separated. Triethylborane/oxygen/ethyl iodide promoted iodine transfer afforded doubly annulated glycosides in a 5-exo-trigonal, 6-endo-digonal cascade. The required re-protection of the three acetoxy groups was carried out orthogonally. The newly installed iodocyclohexene moiety served as site for further functionalization, which was accomplished by metal-halogen exchange followed by electrophilic capture or by reduction/epoxidation.
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