Silaheterocycles. 21. Silene to Silene Rearrangement: Intramolecular [1,3]-Migration of Alkoxy groups

By addition of tert-butyllithium to 1-(trichlorosilyl)-1-(tert-butoxydimethylsilyl)ethene (2) and subsequent LiCl elimination the intermediate 2-(tert-butoxydhnethylsilyl)-1,1-dichloro-2-neopentylsilene (5) is formed. Fast intramolecular [1,3]-migration of the tert-butoxy group yields the unexpected 2-(tert-butoxydichlorosilyl)-1,1-dimethyl-2-neopentylsilene (6), which is trapped by methoxytrimethylsilane, dienes, and quadricyclane. Blocking the target position of the migration by bulky tert-butoxy groups in the silenes Cl_2-n(OBu^t)_nSi=C(SiMe₂OBu^t)CH₂Bu^t (n = 1, 20; n = 2, 27) cannot prevent the rearrangement from taking place. X-ray diffraction studies of the quadricyclane cycloadduct from 2-(di-tert-butoxychlorosilyl)-1,1-dimethyl-2-neopentylsilene (25, C₂₃H₄₃ClO₂Si₂) and NMR spectroscopic studies support these findings. Compound 25 crystallizes in the monoclinic space group P2₁/n and a = 1000.7 (3) pm, b = 1463.5 (3) pm, c = 1780.9 (7) pm, β = 98.02 (1)°, V = 2583 × 10⁶ pm³, and Z -4. A model explaining the reactivity of the C-alkoxysilyl-substituted silenes 5, 17a, 20, and 27 is proposed.