Zeh Dennis, Bast Marcel, Martens Jonathan, Berden Giel, Oomens Jos, Brünken Sandra, Schlemmer Stephan, Schäfer Mathias, Kuck Dietmar
Department of Chemistry, Institute of Organic Chemistry, University of Cologne, Greinstraße 4, 50939 Köln, Germany.
I. Physikalisches Institut, University of Cologne, Zülpicher Straße 77, 50937 Köln, Germany.
J Am Soc Mass Spectrom. 2022 Aug 3;33(8):1377-1392. doi: 10.1021/jasms.2c00039. Epub 2022 Apr 26.
Unidirectional double-hydrogen (2H) and triple-hydrogen (3H) rearrangement reactions occur upon electron-ionization-induced fragmentation of -2-(4-,-dimethylaminobenzyl)-1-indanol (), -2-(4-methoxybenzyl)-1-indanol (), 4-(4-,-dimethylaminophenyl)-2-butanol (), and related compounds, as reported some 35 years ago (Kuck, D.; Filges, U. , , 643-653). These unusual intramolecular redox processes were found to dominate the mass spectra of long-lived, metastable ions. The present report provides independent evidence for the structures of the product ions formed by the 2H and 3H rearrangement in an ion trap instrument. The radical cations and as well as ionized 1-(4-,-dimethylaminophenyl)-5-(4-methoxyphenyl)-3-pentanol, , were generated by electrospray ionization from anhydrous acetonitrile solutions. The 2H and 3H fragment ions were obtained by collision-induced dissociation and characterized by IR ion spectroscopy and density functional theory calculations. Comparison of the experimental and calculated infrared ion spectra enabled the identification of the 2H rearrangement product ion, CHN (/ 136), as an ,-dimethyl--toluidinium ion bearing the extra proton to the amino group, a tautomer which was calculated to be 31 kJ/mol less stable than the corresponding -protonated form. The 3H rearrangement product ion, CHN (/ 123), formerly assumed to be a distonic ammonium ion bearing a cyclohexadienyl radical, was now identified as a conventional radical cation, ionized ,-dimethyl-2,3-dihydro--toluidine. Thus, the 3H rearrangement represents an intramolecular transfer hydrogenation between a secondary alcohol and an ionized aromatic ring. Based on these structural assignments, more detailed mechanisms for the unidirectional 2H and 3H rearrangement reactions are proposed.
约35年前已有报道（库克，D.；菲尔格斯，U. ， ，643 - 653），-2-(4-，-二甲基氨基苄基)-1-茚满醇（）、-2-(4-甲氧基苄基)-1-茚满醇（）、4-(4-，-二甲基氨基苯基)-2-丁醇（）及相关化合物在电子电离诱导裂解时会发生单向双氢（2H）和三氢（3H）重排反应。这些不同寻常的分子内氧化还原过程在长寿命亚稳离子的质谱中占主导地位。本报告为离子阱仪器中由2H和3H重排形成的产物离子结构提供了独立证据。通过电喷雾电离从无水乙腈溶液中产生了自由基阳离子和以及离子化的1-(4-，-二甲基氨基苯基)-5-(4-甲氧基苯基)-3-戊醇（）。通过碰撞诱导解离获得2H和3H碎片离子，并通过红外离子光谱和密度泛函理论计算对其进行表征。实验红外离子光谱与计算光谱的比较使得能够鉴定2H重排产物离子CHN（/ 136）为在氨基上带有额外质子的，-二甲基- -甲苯铵离子异构体，计算得出该异构体比相应的-质子化形式稳定性低31 kJ/mol。3H重排产物离子CHN（/ 123），以前被认为是带有环己二烯基自由基的远距铵离子，现在被鉴定为常规自由基阳离子，即离子化的，-二甲基-2,3-二氢- -甲苯胺。因此，3H重排代表仲醇与离子化芳环之间的分子内转移氢化反应。基于这些结构归属，提出了单向2H和3H重排反应更详细的机理。
