CROSS CAGE INTERACTIONS IN SUBSTITUTED BICYCLO[1.1.]PENT-1-YL RADICALS - DISSOCIATION TO [1.1.1]PROPELLANE

A series of 3-substituted bicyclo[1.1.1]pent-1-yl radicals, including the 3-fluoro derivative, was generated by bromine atom abstraction fro m 1-bromo-3-substituted-bicyclo[1.1.1]pent and examined by EPR spectro scopy. The exceptionally large hyperfine splittings obtained from magn etic nuclei of the 3-substituents indicated that cross cage electronic interactions were substantial in these species. Bromine atom abstract ion by triethylsilyl radicals from 1-bromo-3-fluorobicyclo[1.1.1]penta ne was found to take place more rapidly than bromine abstraction from the unsubstituted parent, i.e., the fluorine substituent mediated a si gnificant polar effect. Evidence was found of a novel disproportionati on process in which the gamma-fluorine atom was transferred from the 3 -fluoro radical to a triethylsilyl or to a second bicyclo[1.1.1]pent-1 -yl radical; an analogous chlorine atom transfer process was found for the 3-chloro radical. Ab initio MO calculations (6-31G basis with el ectron correlation up to MP4) on the 3-fluoro- and 3-methyl-substitute d radicals indicated that loss of the substituent to give [1.1.1]prope llane would be comparatively easy for both species.