Studies toward the Synthesis of Vinigrol. First Construction of the Tricyclic Ring System

The first synthesis of a functionalized tricyclic skeleton of vinigrol is described. The key step involved an anionic oxy-Cope rearrangement of bicyclic allylic alcohol 18, readily prepared by highly stereoselective addition of vinyl magnesium chloride to the hydroxy enone 15b . Introduction of the tertiary hydroxy group at carbon 8a was achieved by an unexpected hydration of 30 with aqueous trifluoroacetic acid.