Angewandte Chemie International Edition
© WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Cover Picture (Angew. Chem. Int. Ed. Engl. 3/1993)
The cover picture shows the space-filling model of a tetraethynyltetrahydro annulene protected fourfold by Si(iPr3)3. Its core is a planar framework of 20 carbon atoms, as the superimposed structural formula clearly indicates. This representation is based on the X-ray crystallographic data of the compound, which is astonishingly stable despite the considerable strain of the central twelve-membered ring. Its electronic absorption spectrum indicates the presence of an antiaromatic [4n] π-electron perimeter, and its purple solutions look remarkably similar to the solutions of C60. More about this compound as well as the analogously constructed annulene, a very promising starting material for new planar hydrocarbon networks, are reported by F. Diederich et al. on pages 406 ff. Also A. de Meijere et al. show with their synthesis of the perspirocyclopropanated rotane (p. 401 ff) a route to new carbon modifications—since the C60 boom a topical field of research.