The selective synthesis of new types of alumosiloxanes can be achieved by the reaction of the bicyclic compound Al
2
[(OPh
2
Si)
2
O]
3
·2 Et
2
O (
3
) with water in donor solvents like acetone or THF, leading to the polycyclic THF adduct [(Ph
2
SiO)
8
(AlO
1,5
)
4
]·2 THF, (
7
), and to the polycyclic alumosiloxane [(Ph
2
SiO)
8
(AlO(OH))
4
]·4 Me
2
C{double bond, long}O (
8
), respectively. In the presence of the base triethylamine, the starting compound
3
gives rise to two other condensation products. At medium temperatures (50–60 °C) in toluene the dispiro alumosilicate [(Ph
2
SiO)
2
O]
2
{Al[(Ph
2
SiO)
2
OH·NEt
3
]}
2
(
9
) is formed and at higher temperatures under reflux in toluene, the product [(Ph
2
SiO)
2
O]Al[(Ph
2
SiO)
2
OH·NEt
3
] (
10
) is generated. The spirocyclic compounds
9
and
10
present the first isolated alumosilicates with six-membered O(SiO)
2
Al cycles. These new types of alumosiloxanes and alumosilicates have been characterised by spectroscopic methods as well as by single crystal X-ray analyses.