The molecular and crystal structures of two derivatives containing 8,11-dioxa[4.3.3]propellane moiety: 8,11-dioxa[3,4-(4 0 -methylbenzo)]-[4.3.3]propellane and 8,11-dioxa[3,4-(4 0

tert -butylbenzo)]-[4.3.3]pro- pellane, were determined and compared with those found for 1,2,4,5-bis{8 0 ,11 0 -dioxa[4.3.3]propel- la(3 0 ,4 0 )}benzene. The discussion of the most stable conformation of cyclohexene and tetrahydrofurane rings for isolated 8,11-dioxa(3,4-benzo)]-[4.3.3]propellane molecule was made using the DFT calcula- tions. The results were compared with those performed for tetraline and 2,2,3,3-tetramethyltetraline. 8,11-Dioxa[3,4-(4 0 -methylbenzo)]-[4.3.3]propellane is important as a reference compound because the unsubstituted 8,11-dioxa(3,4-benzo)-[4.3.3]propellane cannot be obtained in the form of crystalline phase suitable for X-ray diffraction. 1 H NMR spectroscopic analysis showed that the methyl group does not induce expected splitting of the appropriate signals, observed in the case of tert -butyl derivative.