GENERATION OF 4,5-DIAZACYCLOPENTANE-1,3-DIYL RADICAL CATIONS BY CHEMICAL ELECTRON-TRANSFER (CET) OXIDATION OF URAZOLE-BRIDGED BICYCLIC HOUSANES (BICYCLO[2.1.0]PENTANES) AND THEIR CHEMICAL-TRANSFORMATIONS

4,5-Diazacyclopentane-1,3-diyl radical cations 3(.+) were generated fr om urazole-bridged bicyclic housanes 3 through chemical oxidation by u sing tris(4-bromophenyl)aminium hexachloroantimonate as oxidant to aff ord the two olefinic products 4 and 5. Product studies establish that the bisolefins 5 are the result of double oxidation of the housanes 3, whereas the monoolefins 4 are formed by acid-catalyzed rearrangement, which can be suppressed by excess of base (2,6-di-tert-butylpyridine) . In the case of dibenzyl substitution (Sc), disproportionation of two monoradical species 5(H)c(.) serves as an alternative pathway to the corresponding olefins 4 and 5 because higher amounts of double oxidati on product were isolated in the absence of base than expected if only a stoichiometric reaction were operating. Semiempirical MO calculation s suggest that ionization takes place from one of the nitrogen lone pa irs rather than from the strained central C-C bond as implied by the s ignificantly lower (by ca. 0.5 eV) ionization potential. Furthermore, in the initially puckered radical cation, the positive charge is mainl y located at the two nitrogen atoms, while after relaxation to the pla nar geometry, the charge shifts essentially entirely to the radical ca tion carbon atoms. The trapping reaction with methanol leads to the he miaminal-type products 6 and 7, which establish the involvement of the cationic intermediates 3(H)(+) and 5(H)(+). In addition, C-13 NMR spe ctroscopy confirmed these cationic intermediates [3(H)(+) and 5(H)(+)] by detection of the characteristic signals below delta 250 for carben ium ions. Unquestionably, the urazole ring significantly influences th e radical cation reactivity of the housanes 3. Thus, in contrast to th e corresponding homocyclic tricyclooctane derivatives, stoichiometric instead of catalytic amounts of CET oxidant are needed, the two nitrog en atoms of the hydrazino bridge stabilize the radical cation 3(.+) by conjugation, and the carbonyl groups of the urazole moiety assist the deprotonation to the exocyclic double bonds to prevent 1,2 alkyl migr ation.