IPSO NITRATION OF PARA-TERT-BUTYLCALIX[4]ARENES
IPSO NITRATION OF PARA-TERT-BUTYLCALIX[4]ARENES
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DOI：
10.1021/jo00030a050
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发表时间：
1992-02-14
影响因子：
3.6
通讯作者：
REINHOUDT, DN
中科院分区：
文献类型：
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作者：
VERBOOM, W;DURIE, A;REINHOUDT, DN
功能化杯芳烃是一类能络合阳离子和中性分子的重要化合物。1,2杯芳烃可以很容易地在酚羟基（下环）和（部分）去除叔丁基后，在酚环的对位（上环）上官能化。已经报道了几种（选择性）在上缘引入硝基的方法，即直接硝化游离位3、4和取代对磺酸基。在上缘有一个或两个硝基的杯状[4]芳烃也用分步合成法制备了。6,7在本文中，我们描述了（选择性）引入一个或多个硝基，直接取代(a)叔丁基(s)通过对羟基芳香硝化。经过还原后，这些化合物是杯芳烃分子受体的重要起始材料。构象柔韧的5,11,17,23 -四叔丁基- 25,26,27,28 -四甲氧基杯[4]芳烃(1)在二氯甲烷和乙酸1:1的混合物中与过量（20等量）的1007c HN03反应2 h，由乙醇生成四异丙基硝化杯[4]芳烃2，产率为757o。根据核磁共振谱，2以93:7的部分锥形和锥形构象的混合物存在，前者对亚甲基桥质子在4.11和3.45 （AB q）和3.84 (s)的特征吸收，而其中一个甲氧基在3.05的典型单重态吸收。Shinkai等人9将2描述为对四硝基芳烃甲基化后的构象同分异构体的复杂混合物（未进一步分配）。我们还反应了其他四烷基化杯[4]芳烃3,5,7（都是锥形构象）10**得到四硝基杯[4]芳烃4,6，
Functionalized calixarenes represent an important class of compounds that can complex cations and neutral molecules. 1, 2 Calix [4] arenes can easily be functionalized both at the phenolic OH groups (lower rim) and, after (partial) removal of tert-butyl groups, at the para positions of the phenol rings (upper rim). Several methods have been reported for the (selective) introduction ofnitro groups at the upper rim viz. direct nitration of free para positions3, 4 and replacement of p-sulfonate moieties. 1 2345 Calix [4] arenes having one or two nitro groups at the upper rim have also been prepared by a stepwise synthesis. 6, 7 In this paper we describe the (selective) introduction of one or more nitro groups by direct replacement of (a) tert-butyl group (s) via an ipso aromatic nitration. 8 After reduction these compounds are important startingmaterials for molecular receptors based on calixarenes.Results and Discussion Reaction of conformationally flexible 5, 11, 17, 23-tetra-tert-butyl-25, 26, 27, 28-tetramethoxycalix [4] arene (1) with an excess (20 equiv) of 1007c HN03 in a 1: 1 mixture of dichloromethane and acetic acid for 2 h gave upon crys-tallization of the crude reactionmixture from ethanol the tetra-ipso-nitrated calix [4] arene 2 in 757o yield. According to the NMR spectrum, 2 exists as a 93: 7 mixture of the partial cone and cone conformation with for the former characteristic absorptions for the methylene bridge protons at 4.11 and 3.45 (AB q) and 3.84 (s) and the typical singlet of one of the methoxy groups at 3.05. Shinkai et al. 9 described 2 as a complex mixture of conformational iso-mers (not further assigned) upon methylation of p-tetra-nitrocalix [4] arene. We have also reacted the other tetraalkylated calix [4] arenes 3, 5, and 7 (all in the cone conformation) 10** to give thetetranitrocalix [4] arenes 4, 6,