EXPERIMENTAL
1H NMR spectra of compound solutions were measured on a Bruker AM 300 (300 MHz) instrument
using CDCl3. Calibration was carried out using the signal for the residual protons of the solvent at 7.27 ppm.
29Si NMR spectra were recorded using selective polarization transfer from the protons. TLC was carried out on
Silufol UV-254 plates and CHCl3–MeOH (10:1).
Preparation of Compounds 2a-c. Each of compound 1a-c (8.15 mmol) was dissolved in CH2Cl2
(15 ml). (Me3Si)2NH (2 ml, 1.54 g, 9.5 mmol) was added followed by trimethylchlorosilane (1.35 ml, 1.15 g,
10.6 mmol) dropwise with stirring. The reaction product was stirred at room temperature for a further 1 h and
the NH4Cl precipitate was filtered off. The filtrate was evaporated in vacuo and the product was washed with
ether and dried in a desiccator over NaOH.
4,6,8-Trimethyl-2-trimethylsilyl-2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7-dione (2a). Yield 93%;
mp 55°C (decomp.), Rf 0.64. 29Si NMR spectrum, δ, ppm: 9.90 (s, SiMe). Found, %: C 46.75; H 7.94; N 21.93.
C10H20N4O2Si. Calculated, %: C 46.88; H 7.81; N 21.88.
4-Ethyl-6,8-dimethyl-2-trimethylsilyl-2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7-dione (2b). Yield 91%;
mp 58°C (decomp.), Rf 0.72. Found, %: C 48.82; H 8.23; N 20.83. C11H22N4O2Si. Calculated, %: C 48.89;
H 8.15; N 20.74.
6,8-Diethyl-4-methyl-2-trimethylsilyl-2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7-dione (2c). Yield 85%;
mp 52°C (decomp.), Rf 0.81. Found, %: C 50.63; H 8.52; N 19.87. C12H24N4O2Si. Calculated, %: C 50.70;
H 8.45; N 19.72.
Preparation of Compound 3a. Compound 2a (1 g, 3.9 mmol) was dissolved in CH3I (5 ml). AgClO4
(0.9 g, 4.3 mmol) was added with stirring. The reaction mixture was left at room temperature for 2 h and then
diluted with MeOH (10 ml). The precipitated AgI was filtered off, the filtrate evaporated, and the product was
washed with Et2O to give compound 3a (0.41 g, 53%); mp 230-232°C (mp 231-232°C in [6]), Rf 0.54.
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