Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore.
Chemistry. 2011 Aug 29;17(36):10081-8. doi: 10.1002/chem.201101363. Epub 2011 Jul 21.
A synthetic method that relies on gold-catalysed cyclopropyl carbinol rearrangement of 2-tosylaminophenyl cyclopropylmethanols to prepare 2,3-dihydro-1H-benzo[b]azepines and 2-vinylindolines efficiently is reported. The reactions were shown to be chemoselective, with secondary and tertiary alcohol substrates exclusively providing benzo-fused five- and seven-membered ring products, respectively. The ring-forming process was also found to proceed in moderate to excellent yields under mild conditions only in the presence of the gold and silver catalyst combination. The mechanism is thought to involve activation of the alcohol by the (p-CF(3)C(6)H(4))(3)PAuCl/AgOTf (Tf = triflate) catalyst, resulting in ionization of the starting material. The tertiary carbocationic intermediate generated in situ in this manner then triggers ring-opening of the cyclopropane moiety and trapping by the tethered aniline group to give the 2,3-dihydro-1H-benzo[b]azepine. Cyclopropane ring fragmentation of the secondary carbocationic analogue, on the other hand, results in diene formation followed by subsequent intramolecular hydroamination to afford the 2-vinylindoline.
本文报道了一种通过金催化的 2-对甲苯磺酰氨基苯基环丙甲醇的环丙基甲醇重排反应来高效制备 2,3-二氢-1H-苯并[b]氮杂卓和 2-乙烯基吲哚啉的合成方法。反应具有化学选择性，只有仲醇和叔醇底物分别提供苯并稠合的五元环和七元环产物。研究还发现，在温和条件下，仅在金和银催化剂组合的存在下，该环形成过程就能以中等至优异的产率进行。该反应的机理被认为涉及醇被（p-CF3C6H4）3PAuCl/AgOTf（Tf = 三氟甲磺酸根）催化剂活化，从而导致起始物质的电离。以这种方式原位生成的叔碳阳离子中间体随后引发环丙烷部分的开环，并与连接的苯胺基团发生捕获反应，得到 2,3-二氢-1H-苯并[b]氮杂卓。另一方面，仲碳阳离子类似物的环丙烷环断裂导致二烯形成，随后进行分子内氢胺化，得到 2-乙烯基吲哚啉。
