OXIDATION OF STERICALLY CROWDED ALKYL(CYCLOALKYL)PYRENES - PERSISTENT DICATIONS IN SBF5/SO2CLF AND RADICAL CATIONS IN FSO3H/SO2

Sterically crowded alkylpyrenes 2-7 undergo two-electron oxidation with SbF5/SO2ClF (or SbF5.FSO3H (9:1)/SO2ClF) to give persistent alkylpyrene dications. In agreement with the charge distribution pattern observed in the parent pyrene dication and with semiempirical calculations (AM1) on isomeric monoisopropylpyrenes dications; the deshielding order C(alpha) > C(alphabeta) > C(beta) was found in their carbon-13 NMR spectra regardless of the number and position of the alkyl substituents. In most cases, the observed DELTAdelta13C for the aromatic ipso-carbon signals of the alkylpyrenium dications relative to those of 1(+2) were slightly larger than expected for a normal substituent effect in the alkylpyrene precursors. Only minor changes (DELTAdelta13C) in the unsubstituted positions were observed, except for the ring carbons in highly crowded locations for which a noticeable upfield shift was detected. The H-1 NMR spectra of alkylpyrenium dications showed a much greater substituent dependency. Low temperature reactions of the less-reactive pyrene and 2,7-di-tert-butylpyrene with SbF5/SO2ClF led primaryl to sulfonylation sigma-complexes rather than oxidation dications. Persistent alkylpyrene radical cations were found to coexist with the alkylpyrenium ions of protonation in FSO3H/SO2 (ESR detection) without any noticeable line broadening in the NMR spectra of the Wheland intermediates.