PENTAGONAL DODECAHEDRANES - NOVEL SUBSTITUTION PATTERNS - MS FRAGMENTATION AND UNSATURATION

For two-to six-fold functionalised dodecahedranes (7-10) the chances f or selective variation of their substitution have been explored, as pa rt of a program directed at homododecahedranes and at highly unsaturat ed dodecahedranes, ultimately C-20 fullerene. With 1,6-dimethyl ester 7 several side chain transformations next to the very bulky dodecahedr al cage were effected (1,6-bismethylene derivatives 25-31). In changin g environments, Barton-type halogenative/hydrogenative decarboxylation s (15-17, 38, 49, 59, 60, 77) as well as various nucleophilic substitu tions (18, 20, 23, 39, 61-64) were achieved, mostly with good to high efficiency and retention of the substitution patterns. For the cage ol efins 8/9 and the diepoxide 10, front-side cis-1,2-addition faced only slight competition in the reactions with HBr and CF3CO2H, but was onl y a minor pathway in the reaction with Br-2, In the latter case, by a sequence of Br+ addition/HBr elimination steps, up to nine vicinally p laced bromine substituents were implanted upon the C-20 skeleton. The fate of variously functionalised dodecahedranes upon electron impact w as studied-the competition between external (C-X/Y) and internal (C-C) bond cleavage was found to be typically dependent on the nature and r elative orientation of the functionalities (X,Y) involved. There is go od evidence that ions between m/z 242 (C20H2) and 256 (C20H16) resulti ng from the elimination of the respective Br, CO2CH3, CO2NH2, OCOCF3 s ubstituents represent unsaturated dodecahedranes with up to nine C=C d ouble bonds.