2-acetyl-10-acetoxy-6-(tert-butyldimethylsiloxy)-3,4-(isopropylidenedioxy)-12,12-(2',2'-dimethylpropane-1',3'-diyldioxy)-11-oxo-3(S*),4(R*),4a(S*),5,5a(S*),6(S*),11a(R*),12,12a(S*)-decahydronaphthacene