Synthesis of highly hindered oxepins and an azepine from bis-trityl carbenium ions: structural characterisation by NMR and X-ray crystallography
作者:Kieran A. Carey、William Clegg、Mark R. J. Elsegood、Bernard T. Golding、M. N. Stuart Hill、Howard Maskill
DOI:10.1039/b207108h
日期:2002.11.26
Reactions of the bis-carbenium ion 2,2′-bis[bis(p-methoxyphenyl)methyl]biphenyl ditetrafluoroborate with ammonia, n-propylamine and benzylamine have been studied with the aim of developing an acid-labile protecting group for primary amines that masks both hydrogen atoms of the NH2 group. Although the parent 5,5,7,7-tetrakis(p-methoxyphenyl)-5,7-dihydrodibenzo[c,e]azepine was isolated and fully characterised, the corresponding azepines could not be obtained in a pure state from the reactions with the primary amines. The bis-carbenium ion was prepared from the treatment of 2,2′-bis[bis(p-methoxyphenyl)hydroxymethyl]biphenyl with fluoroboric acid. Attempts to prepare the corresponding diphenyl analogue were unsuccessful using either fluoroboric acid or boron trifluoride. The only product isolated from these reactions was 5,5,7,7-tetraphenyl-5,7-dihydrodibenzo[c,e]oxepin. The oxepin and its phenyl-p-methoxyphenyl and bis(p-methoxyphenyl) analogues were efficiently obtained by dehydration of the corresponding diol, e.g. 2,2′-bis[bis(p-methoxyphenyl)hydroxymethyl]biphenyl, in the presence of 3 Å molecular sieves or Amberlite IR-200 resin. The compounds 2,2′-bis[bis(p-methoxyphenyl)hydroxymethyl]biphenyl, (R,R/S,S)-2,2′-[bis(phenyl-p-methoxyphenyl)hydroxymethyl]biphenyl, 5,5,7,7-tetraphenyl-5,7-dihydrodibenzo[c,e]oxepin, 5,5,7,7-tetrakis(p-methoxyphenyl)-5,7-dihydrodibenzo[c,e]oxepin and 5,5,7,7-tetrakis(p-methoxyphenyl)-5,7-dihydrodibenzo[c,e]azepine were characterised by crystal structure analyses. 2,2′-Bis[bis(p-methoxyphenyl)hydroxymethyl]biphenyl and 5,5,7,7-tetrakis(p-methoxyphenyl)-5,7-dihydrodibenzo[c,e]oxepin exhibited dynamic NMR properties, and free energy barriers have been determined.
我们研究了双硒离子 2,2′-双[双(对甲氧基苯基)甲基]联苯二四氟硼酸盐与氨、正丙胺和苄胺的反应,目的是开发一种可掩盖 NH2 基团两个氢原子的伯胺酸性保护基团。虽然母体 5,5,7,7-四(对甲氧基苯基)-5,7-二氢二苯并[c,e]氮杂卓已经分离出来并完全定性,但相应的氮杂卓却无法从与伯胺的反应中获得纯净的状态。氟硼酸处理 2,2′-双[双(对甲氧基苯基)羟甲基]联苯后制备出了双羧鎓离子。使用氟硼酸或三氟化硼制备相应的二苯基类似物的尝试都不成功。从这些反应中分离出的唯一产物是 5,5,7,7-四苯基-5,7-二氢二苯并[c,e]氧杂卓。在 3 Å 分子筛或 Amberlite IR-200 树脂存在的情况下,通过对相应的二元醇(如 2,2′-双[双(对甲氧基苯基)羟甲基]联苯)进行脱水,可以有效地获得氧杂卓及其苯基-对甲氧基苯基和双(对甲氧基苯基)类似物。化合物 2,2′-双[双(对甲氧基苯基)羟甲基]联苯、(R,R/S,S)-2,2′-[双(苯基-对甲氧基苯基)羟甲基]联苯、5,5,7,7-四苯基-5,7-二氢二苯并[c,e]氧杂卓、5,5,7,7-四(对甲氧基苯基)-5,7-二氢二苯并[c,e]氧杂卓和 5,5,7,7-四(对甲氧基苯基)-5,7-二氢二苯并[c,e]氮杂卓的晶体结构分析。2,2′-双[双(对甲氧基苯基)羟甲基]联苯和 5,5,7,7-四(对甲氧基苯基)-5,7-二氢二苯并[c,e]氮杂卓显示了动态核磁共振特性,并测定了自由能垒。