Thionation of the monoacetal of pentacyclo[5.4.0.02,6.03,10.55,9]undecane-8,11-dione

As part of a programme to synthesize thione derivatives with pentacyclo[5.4.0.0 2 , 6 .0 3 , 1 0 .0 5 , 9 ]undecane moieties it was decided to sulfurize the monoacetal 6 of pentacyclo[5.4.0. 2 , 6 .0 3 , 1 0 .0 5 , 9 ]undecane-8,11-dione 2. Unexpectedly the diol 9 was isolated as the product.