The osmylation of dienic sulfone 4, a potential key intermediate in fo
rskolin 1 and polyhydroxylated drimanes or labdanes derivatives, occur
red exclusively on the Delta(6-7) double bound and preferentially from
the alpha-face of the molecule (40-100% de). The influence of the sub
stituent at C-l on the stereoselectivity of the reaction is studied.