The selective synthesis of new types of alumosiloxanes can be achieved by the reaction of the bicyclic compound Al2[(OPh2Si)2O]3·2 Et2O (3) with water in donor solvents like acetone or THF, leading to the polycyclic THF adduct [(Ph2SiO)8(AlO1,5)4]·2 THF, (7), and to the polycyclic alumosiloxane [(Ph2SiO)8(AlO(OH))4]·4 Me2C{double bond, long}O (8), respectively. In the presence of the base triethylamine, the starting compound3gives rise to two other condensation products. At medium temperatures (50–60 °C) in toluene the dispiro "alumosilicate" [(Ph2SiO)2O]2{Al[(Ph2SiO)2OH·NEt3]}2(9) is formed and at higher temperatures under reflux in toluene, the product [(Ph2SiO)2O]Al[(Ph2SiO)2OH·NEt3] (10) is generated. The spirocyclic compounds9and10present the first isolated "alumosilicates" with six-membered O(SiO)2Al cycles. These new types of alumosiloxanes and "alumosilicates" have been characterised by spectroscopic methods as well as by single crystal X-ray analyses.