title: Bromination of unsaturated dodecahedranes--en route to C20 fullerene.
abstract: As part of a study to achieve selective oligo(poly)bromination-ultimately perbromination-of the dodecahedral C(20) skeleton, the extent and direction of the ionic bromination of dodecahedrene and 1,16-dodecahedradiene were explored. Along sequences of Br(+) additions/deprotonations and allylic rearrangements, up to ten hydrogen atoms were substituted (traces of C(20)H(x)Br(10)). Tetrabromododecahedrenes obtained under defined conditions in up to 50 % total yield with three and four allylic bromine substituents protecting the extremely bent C==C bonds, proved highly unreactive even towards oxygen but reacted rapidly with CH(2)N(2). Upon electron impact ionization (MS) of the newly secured oligo(poly)bromododecahedra(e)nes, sequential loss of the substituents ended generally in polyunsaturated dodecahedranes (in the extreme C(20)H(4), "tetrahydro-C(20) fullerenes"). Only subsequently did skeletal fragmentations occur. From X-ray crystal-structure analyses, more information was obtained on the structural response of the dodecahedral skeleton to the strain induced by the voluminous substituents. As Appendix, the forcing radical bromination of 1,6-dibromododecahedrane and exploratory cis-beta-HBr/cis-beta-Br(2) eliminations in bromododecahedranes with [Fe(2)(CO)(9)], P(2)F/[FeCp(2)] and [Fe(tmeda)Cp*Cl] (in situ protection) are presented.
authors.affiliation: Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, 79104 Freiburg, Germany.
authors.forename: Emmerich
authors.initials: E
authors.lastname: Sackers
authors.forename: Thomas
authors.initials: T
authors.lastname: Osswald
authors.forename: Klaus
authors.initials: K
authors.lastname: Weber
authors.forename: Manfred
authors.initials: M
authors.lastname: Keller
authors.forename: Dieter
authors.initials: D
authors.lastname: Hunkler
authors.forename: Jürgen
authors.initials: J
authors.lastname: Wörth
authors.forename: Lothar
authors.initials: L
authors.lastname: Knothe
authors.forename: Horst
authors.initials: H
authors.lastname: Prinzbach