2,4-dione (2,4-stelladione, 3), tri-toelectron spectra of 3, 5, and 4-methylenetricyclo-[3.3.0.0 3,7 ]octan-2-one (9) were recorded and interpreted on cyclo[3.3.0.0 3,7 ]octane-2,6-dione (2,6-stelladione, 4), and 2oxotricyclo[3.3.0.0 3,7 ]octane-6-thione (5) were synthesized.
the basis of quantum-mechanical calculations (HF-SCF, 6-31G* basis). The large energy difference between the first Key steps in the procedures were a Paterno-BΓΌchi reaction followed by an oxetane splitting with a strong base. Structure PE bands of 3 (0.8 eV) is due to a strong interaction between the lone pairs on the oxygen atoms and the Ο frame. analysis on single crystals of 4 and 5 revealed long central CΟͺC bonds (1.59 A Λ) of the stellane skeleton. The He(I) pho-
We have synthesized and investigated a number of hydro-Nakazaki et al. [7] . The starting point in this protocol was endo-2-acetylbicyclo[2.2.1]hept-5-ene (6) [7] which was trans-carbons containing the tricyclo[3.3.0.0 3,7 ]octane (stellane) skeleton [1] in the past years. These investigations were formed to 2-methyl-3-oxatetracyclo[4.2.1.0 2,5 .0 4,8 ]nonane ( 7) by an intramolecular Paterno-BΓΌchi reaction (Scheme undertaken for several reasons: Calculations suggested a strong interaction between two exo double bonds in 2,6-1). Treatment of 7 with a strong base allowed the abstraction of a proton from the CH 3 group and opened the oxet-and 2,4-stelladienes (1, 2) which could be verified by means of PE spectroscopy [2] . A second point of interest was that ane ring. The resulting 4-methylenetricyclo[3.3.0.0 3,7 ]octan-2-ol (8) was readily oxidized to 9. Further oxidation with two stellanes could be coupled together to build a rigid molecular scaffold to study long range interactions [3] . Further-ozone yielded tricyclo[3.3.0.0 3,7 ]octane-2,4-dione (3). more 1, 2, and its congeners proved to be interesting models Scheme 1 for studying a stepwise Cope rearrangement [4] . Key compounds in the syntheses of the model systems were the corresponding diketones tricyclo[3.3.0.0 3,7 ]octane-2,4-dione (2,4-stelladione, 3) and tricyclo[3.3.0.0 3,7 ]octane-2,6-dione (2,6-stelladione, 4). In this paper we report on the syntheses of 3, 4, and the thioketone 5.