Search for long-lived 1,3-carbodications and preparation of the persistent1,1,3,3-tetracyclopropyl-1,3-propanediyl dication

Several substituted versions of 1,3-propanediol were ionized under a variet y of superacidic conditions, and the product carbocations and carboxonium s pecies were characterized by C-13 NMR spectroscopy at low temperatures. 1,1 ,3-Triphenyl-1,3-propanediol(19), and 1,1,3,3-tetraphenyl-1,3-propanediol ( 20), upon ionization in FSO3H/SO2ClF or SbF5-FSO3H/SO2ClF solution at -78 d egrees C gave the disproportionated cationic species, 1,1-diphenylethyl cat ion (24) and protonated benzaldehyde (25) or protonated benzophenone (26). At lower temperatures (-130 degrees C) they yielded the allyl cations, 29 a nd 30, as the only products. Diol 23 was also ionized at -78 degrees C to g ive a I:1 mixture of tricyclopropylmethyl cation (27) and O-protonated dicy clopropyl ketone (28). The ionization of 1,1,3,3-tetracyclopropy1-1,3-propa nediol (21) in SbF5/SO2ClF, on the other hand, gave the stable 1,3-carbodic ation, that is, 1,1,3,3-tetracyclopropy1-1,3-propanediyl dication (33). The structures and the C-13 NMR chemical shifts for the carbodication 33 and t he allyl cations 29 and 30 were also computed using DFT/IGLO methods.