The dihedral angles of Si‐Si‐Si‐Si frameworks were controlled to ∼10°(S), 180°(A), and ∼120°(E) by the use of the syn‐ and anti‐disilane units that are configurationally constrained by two pentamethylene tethers. The UV absorption spectra of the tetrasilanes (see picture) were found to be consistent with the new explanation proposed by Michl and co‐workers for the UV absorption of polysilane compounds.

On the basis of the UV absorption spectra of the anti,cisoid alternating oligosilanes, the first experimental clear-cut evidence was presented for the generally accepted idea that the sigma conjugation in polysilanes does not effectively extend through a tetrasilane fragment with a small dihedral angle such as a cisoid turn.

No abstract

Steric protection of the selenium atom in the episelenonium ion intermediate by the bulky 2,4,6-tri-tert-butylphenyl (TTBP) group has been utilized in the selective formation of carbocyclic compounds from the substrate bearing a β-oxyselenide unit and a double bond in the same molecule.