NMR and DFT studies on persistent carbocations derived from benzo[kl]xanthene, dibenzo[d,d ']benzo[1,2-b:4,3-b ']difuran, and dibenzo[d,d']benzo[1,2-b:4,5-b ']difuran in superacidic media

作者：Okazaki Takao^*; Nakagawa Madoka; Futemma Takeshi; Kitagawa Toshikazu

来源：Journal of Physical Organic Chemistry, 2016, 29(2): 107-111.

DOI：10.1002/poc.3505

• carbocation
• DFT
• NMR
• polycyclic aromatic compound
• superacid

Persistent carbocations generated by the protonation of hetero-polycyclic aromatic compounds with oxygen atom(s) were studied by experimental NMR and density function theory calculations. Benzo[kl]xanthene (1), dibenzo[d,d']benzo[1,2b: 4,3-b']difuran (2), and dibenzo[d,d']benzo[1,2-b:4,5-b']difuran (3) were synthesized by the annulation of arenediazonium salts. Compound 1 in FSO3H-SbF5 (4: 1)/SO2ClF and 3 in FSO3H-SbF5 (1:1)/SO2ClF ionized to 1aH(+) with protonation at C(4) and to 3aH(+) with protonation at C(6), and these cations were successfully observed by NMR at low temperatures. The density function theory calculations indicated that 1aH(+) and 3aH(+) were the most stable protonated carbocations and that 2 should ionize to 2aH(+) with protonation at C(6). According to the changes in C-13 chemical shifts (Delta delta C-13), the positive charge was delocalized into the naphthalene unit for 1aH(+), into one benzo[b,d]furan unit for 2aH(+), and into one benzo[b,d]furan unit for 3aH(+).

• 出版日期2016-2