Intramolecular [3 + 2]-Hetero-Annulation of Allylsilanes with 1,3-Cyclohexanediones and its Application in the Synthesis of Hexacyclic Hopane Triterpenes - Schinzer, Dieter; Müller, Norbert; Fischer, Axel K; Prieß, Jan W (Synlett, 2000)