Unambiguous detection of 2,4,6-cycloheptatrien-1-ol by NMR spectroscopy and trapping with phenyltriazolinedione

For the first time, the title alcohol 3 was unambiguously detected as a transient intermediate leading to ditropylether (6) in a cation-anion reaction between the tropylium ion (5) and hydroxide ion in an aqueous solution by NMR spectroscopy. It was also found that 6 gives 3 as a transient product in acid-catalyzed disproportionation of 6 into a mixture of tropone (4) and 1,3,5-cycloheptatriene (7) in chloroform containing water. Furthermore the existence of 3 in the latter reaction was confirmed by trapping with 4-phenyl-1,2,4-triazoline-3,5-dione to afford the [4+2]cycloadduct of the norcaradiene form of 3. (C) 2003 Elsevier Science Ltd. All rights reserved.