Although protic solvents are generally not preferred for nucleophilic displacement reactions because of their partial positive charge and hydrogen-bonding capacity that solvate the nucleophile and reduce its reactivity, we recently reported a remarkably beneficial effect of using tertiary alcohols as a reaction media for nucleophilic fluorination with alkali metal fluorides, as well as fluorine-18 radiolabeling with [¹⁸F]fluoride ion for the preparation of PET radiopharmaceuticals. In this work, we investigate further the influence of the tert-alcohol reaction medium for nucleophilic fluorination with alkali metal fluorides by studying various interactions among tert-alcohols, the alkali metal fluoride (CsF), and the sulfonyloxy substrate. Factors such as hydrogen bonding between CsF and the tert-alcohol solvent, the formation of a tert-alcohol solvated fluoride, and hydrogen bonding between the sulfonate leaving group and the tert-alcohol appear to contribute to the dramatic increase in the rate of the nucleophilic fluorination reaction in the absence of any kind of catalyst. We found that fluorination of 1-(2-mesyloxyethyl)naphthalene (5) and N-5-bromopentanoyl-3,4-dimethoxyaniline (8) with Bu₄N⁺F^- in a tert-alcohol afforded the corresponding fluoro products in much higher yield than obtained by the conventional methods using dipolar aprotic solvents. The protic medium also suppresses formation of byproducts, such as alkenes, ethers, and cyclic adducts.

中文翻译：

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使用叔醇作为反应介质的容易的亲核氟化反应：显着增强了碱金属氟化物的反应性并提高了选择性

尽管质子溶剂通常不优选用于亲核取代反应，因为它们具有部分正电荷和氢键合能力，可溶解亲核试剂并降低其反应性，但我们最近报道了使用叔醇作为反应介质进行亲核氟化的显着有益效果。碱金属氟化物，以及[ ¹⁸ F]氟离子对¹⁸氟进行放射性标记，以制备PET放射性药物。在这项工作中，我们进一步研究的影响叔通过研究之间的各种相互作用与碱金属氟化物亲核氟化-醇反应介质叔-醇，碱金属氟化物（CsF）和磺酰氧基底物。诸如CsF和叔醇溶剂之间的氢键，叔醇溶剂化氟化物的形成以及磺酸盐离去基团和叔醇之间的氢键等因素似乎有助于亲核试剂速率的急剧增加。在没有任何催化剂的情况下进行氟化反应。我们发现1-（2- mesyloxyethyl）萘（那氟化5）和Ñ -5-溴戊基-3,4-二甲氧基苯胺（8）配有卜₄ Ñ ⁺ ˚F ^-在叔-醇比使用偶极非质子溶剂的常规方法获得的产率高得多，提供了相应的氟代产物。质子介质还抑制副产物的形成，例如烯烃，醚和环状加合物。