Bicyclo(3.3.1)nonanes as synthetic intermediates. XVII. A novel interconversion between bicyclo(4.3.1)decane and tricyclo(4.3.1.0)decane systems via the dual mode of aldol cyclization of bicyclo(4.3.1)decane-3,8-dione.

The characteristics intramolecular aldol cyclization of bicyclo[4.3.1]decanedione to two novel tricyclic systems, protoadamantanone and isotwistanone, is described. Both systems were reconverted to bicyclo[4.3.1]decanones by the Grob fragmentation.