Generation of 1,6-Disilahexapentaene in the Reduction of an Overcrowded Bis(bromodiaryl) butadiyne Leading to the Unexpected Formation of 2-Allenyl-1-benzosilole

When the reductive debromination of an overcrowded bis(bromodiarylsilyl)butadiyne (2) bearing Tbt and Mes groups was performed with potassium graphite, the corresponding 2-allenyl-1-benzosilole (3) was isolated as a main product. The formation of 3 was most likely interpreted in terms of the initial generation of 1,6-disilahexapentaene (1) followed by the intramolecular double cyclization.