A bowl-shaped, bicyclic diol compound was synthesized by intramolecular twofold aldol condensation reaction of a decane-2,4,7,9-tetraone derivative. Two hydroxy groups at the concave side of the bicyclic compound provided convergent reaction sites for silylation. Reaction with tetrachlorosilane furnished two spirosilicate-type dimers that were remarkably stable toward hydrolysis as compared to other tetraalkoxysilanes.