EXPLORATORY SYNTHETIC STUDIES INVOLVING THE TRICYCLO[9.3.0.0(2,8)]TETRADECANE RING-SYSTEM PECULIAR TO THE CYATHINS

Following an improved preparation of 2-methylene-1,3-dithiolane, this ketene acetal was shown to undergo inverse-electron-demand Diels-Alder cycloaddition to tropone. Regiocontrolled copper hydride reduction and resolution via sulfoximine adducts was readily achieved to give (-)-9. Addition to 9 of the chiral nonracemic vinyl bromides 21 and 22 proceeded with endo capture of the nucleophilic vinyllithium to give carbinols that underwent anionic oxy-Cope rearrangement at somewhat elevated temperatures. The [3,3] sigmatropic event delivered cis,syn,cis-tricyclo[9.3.0.0(2,8)]tetradecnones possessing structural frameworks related to the cyathins. Once 31 was in hand, it proved an easy matter to introduce added unsaturation and oxygen substituents. The tendency of certain derivatives for transannular cyclization was made quite apparent. Attempts to introduce a C(6)-alpha-methyl substituent was not achieved, chiefly as the result of the overall molecular concavity of this class of intermediates. A variety of reactions aimed at enhancing the level of functionality in rings B and C was explored and processes conducive to the attainment of these goals were developed.