A CONCISE ROUTE TO THE TETRACYCLIC CORE OF PHORBOL

Article abstract of DOI:10.1016/S0040-4020(01)86705-3

The tetracyclic ketone 17, which possesses a framework closely related to phorbol, has been prepared in enantiomerically pure condition.Condensation of the dichlorocerate derived from 3 with 2-chlorocyclohexanone leads to chlorohydrins 4 and 5 in a 1:1 ratio.Treatment of 5 with excess vinylmagnesium bromide delivers 7, thereby setting the stage for anionic oxy-Cope rearrangement to 9.Epoxidation of 9 and base-promoted cyclization of the α-isomer (15) under kinetically controlled conditions eventuates in the formation of 17.A companion set of reactions was performed on 4 with the result that hemiketal 11 is formed following transannular ring closure.Lastly, one of the first intramolecularly competitive anionic oxy-Cope rearrangements is described.