Search for Long-Lived 1,3-Carbodications and Preparation of the Persistent 1,1,3,3-Tetracyclopropyl-1,3-propanediyl Dication1

Abstract

Several substituted versions of 1,3-propanediol were ionized under a variety of superacidic conditions, and the product carbocations and carboxonium species were characterized by 13C 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 °C gave the disproportionated cationic species, 1,1-diphenylethyl cation (24) and protonated benzaldehyde (25) or protonated benzophenone (26). At lower temperatures (−130 °C) they yielded the allyl cations, 29 and 30, as the only products. Diol 23 was also ionized at −78 °C to give a 1:1 mixture of tricyclopropylmethyl cation (27) and O-protonated dicyclopropyl ketone (28). The ionization of 1,1,3,3-tetracyclopropyl-1,3-propanediol (21) in SbF5/SO2ClF, on the other hand, gave the stable 1,3-carbodication, that is, 1,1,3,3-tetracyclopropyl-1,3-propanediyl dication (33). The structures and the 13C NMR chemical shifts for the carbodication ...