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Three stable 1-silapropadienes 1a−c were prepared by the intermolecular addition of organolithium reagents at the carbon−carbon triple bond of fluoroalkynylsilanes 3a,b followed by LiF elimination. The structure of 1a and of the intermediate α-lithiated fluorosilane 2a were determined by X-ray diffraction. The chemical behavior of 1-silapropadienes 1a−c differs greatly depending on the substituents on the silicon atom. When two triisopropylphenyl groups were present (1a), typical addition reactions of the SiC double bond were observed. Thermolysis of 1a yielded benzosilacyclobutene 7. For the more hindered 1-silapropadienes 1b and 1c, no reaction was observed with dioxygen, benzaldehyde, 2,3-dimethylbutadiene, or trimethylchlorosilane at room temperature. However, thermolysis of 1b or treatment with excess ethanol under neutral or acidic conditions produced 8b, the product of an intramolecular insertion of the SiC double bond into an adjoining primary C−H bond of one tert-butyl group in an ortho-position of the supermesityl substituent. In the presence of EtOD and catalytic D2SO4, this reaction occurred very rapidly at −78 °C with over 95% incorporation of deuterium in the product.

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The First Stable 1-Silaallene. -The title compound (II) is stable in the presence of air and water under nonacidic conditions. The structure of (II) is confirmed by X-ray analysis. -(MIRACLE, G. E.; BALL, J. L.; POWELL, D. R.; WEST, R.; J.