Toward the Total Synthesis of Vinigrol: Synthesis of epi-C-8-Dihydrovinigrol

Two approaches to vinigrol starting from the advanced tricyclic core 7 have been explored using as key intermediates epoxide 12 and diol 17. The preparation of the properly functionalized epoxide 12 has been achieved in a straightforward fashion. However, all attempts to prepare tertiary alcohol 14 by reductive opening of 12 failed. In alternative exploratory efforts to achieve the same goal, allylic alcohols 16 and 29 were prepared by regioselective dehydration of diol 17. Whereas endo-isomer 16 was found to be reluctant to undergo catalytic hydrogenation, the exo counterpart 29 led to the undesired isomer affording after hydrolysis epi-C-8-dihydrovinigrol 32.