脒二阳离子作为超亲电试剂。

WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, United Kingdom.

J Am Chem Soc. 2009 Dec 16;131(49):17980-5. doi: 10.1021/ja908191k.

2-Dimethylalkylammonium pyridinium and 2-dimethylalkylammonium pyrimidinium ditriflate salts are very powerful methylating agents toward phosphorus (triphenylphosphine) and nitrogen (triethylamine) nucleophiles. In competition experiments with triethylamine as nucleophile, these N-methyl disalts are more reactive methylating agents than dimethyl sulfate. Reaction of the pyridinium dications with water as an oxygen nucleophile leads to attack at the 2-position of the heteroaromatic ring and displacement of an ammonium group; 2-hydroxypyridinium compounds are formed in the first instance, which are easily converted to 2-pyridones. Extending the scope of the reactions, a tricationic 2,6-bis(dimethylalkylammonium)pyridinium salt has also been prepared and characterized and its reactivity as a methylating agent assessed in comparison with that of the dications.

2-二甲基烷基铵吡啶鎓和 2-二甲基烷基铵嘧啶鎓三氟甲磺酸酯盐是非常有效的磷（三苯基膦）和氮（三乙胺）亲核试剂的甲基化试剂。在与三乙胺作为亲核试剂的竞争实验中，这些 N-甲基双盐是比硫酸二甲酯更具反应性的甲基化试剂。吡啶鎓二阳离子与水作为氧亲核试剂反应导致在杂芳环的 2-位进行攻击，并取代铵基团；首先形成 2-羟基吡啶化合物，其容易转化为 2-吡啶酮。扩展反应范围，还制备和表征了一种三阳离子 2,6-双（二甲基烷基铵）吡啶鎓盐，并评估了其作为甲基化试剂的反应性，与二阳离子进行了比较。