Fused Tricyclic Disilenes with Highly Strained SiSi Double Bonds: Addition of a SiSi Single Bond to a SiSi Double Bond

Internal fusion: The stable fused tricyclic tetraalkyl disilenes cis-1 and trans-1 were synthesized as yellow and red-purple crystals, respectively (see picture). X-ray analysis has shown that the geometry around the SiSi bond in trans-1 is unusually distorted, but is rather normal in cis-1. Disilene trans-1 isomerizes stereospecifically to a tetracyclic isomer by unprecedented addition of a SiSi single bond to a SiSi double bond.