Sterically hindered p-nitrobenzylic chlorides (1) and
(2) react with the sodium salts of 2,4,6-trialkylbenzenethiols (3a)–(5a)
by the SRN1 reaction to give good yields of the
corresponding p-nitrobenzylic aryl sulfides
(6)–(10). For example, the reaction of sodium
2,4,6-triisopropylbenzenethiolate (4b) with
α-t-butyl-a-methyl-p-nitrobenzyl chloride (2)
gives the sulfide (10) in over 80% yield after 2 h at room temperature
in Me2SO. Only in reactions involving
2,4,6-tri-t-butylbenzenethiol (5a) are low yields or failed reactions
encountered. Qualitative examination of the dynamic nuclear magnetic resonance
spectra of the sulfides prepared in these reactions shows that up to three
restricted rotational phenomena can be identified. These are rotation about
the benzylic-carbon to p-nitrophenyl ring bond, rotation
about the sulfur to aromatic ring bond, and rotation about the bond joining
the t-butyl group to the benzylic carbon. The last phenomenon produces, in the
sulfide (9), the relatively rare and unusual situation wherein the t-butyl
group appears as three distinct methyl resonances at low temperatures.
受立体阻碍的对硝基苄基氯(1)和(2)
(2) 与 2,4,6-三烷基苯硫醇钠盐 (3a)-(5a) 通过 SRN1 反应
的钠盐发生 SRN1 反应,从而得到产率很高的
相应的对硝基苄基芳基硫化物
(6)-(10).例如,钠
2,4,6-三异丙基苯硫酚钠(4b)与
α-叔丁基-a-甲基对硝基苄基氯(2)反应
在室温下于 Me2SO 溶液中反应 2 小时后,得到硫化物 (10),收率超过 80%。
Me2SO。只有在涉及
2,4,6-三丁基苯硫酚 (5a) 的反应中,才会出现产率低或反应失败的情况。
或反应失败。动态核磁共振光谱的定性检查
光谱显示,在这些反应中制备的硫化物最多可发现三种
限制性旋转现象。这些旋转现象是
围绕苄碳到对硝基苯环键的旋转、围绕硫到芳香环键的旋转、围绕硫到芳香环键的旋转。
硫与芳香环键的旋转,以及连接叔丁基与苄基环键的旋转。
和连接叔丁基和苄基碳的键的旋转。最后一种现象在
硫化物 (9)中,出现了相对罕见和不寻常的情况,即叔丁基出现了三个不同的甲基共振。
基团在低温下出现三个不同的甲基共振。