Platinnm-catalyzed multistep reactions of indoles with alkynyl alcohols
Platinnm-catalyzed multistep reactions of indoles with alkynyl alcohols
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DOI：
10.1002/chem.200700589
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发表时间：
2007-01-01
影响因子：
4.3
通讯作者：
Cheng, Chien-Hong
中科院分区：
文献类型：
--
作者：
Bhuvaneswari, Sivakolundu;Jeganmohan, Masilamani;Cheng, Chien-Hong
PtCl_2有效地催化N-甲基吲哚（1a）与3-炔-1-醇（2a）在THF中的多步反应，在室温下反应21 t，以93%的产率得到C3位含五元环醚基的吲哚衍生物3a。在类似的反应条件下，各种取代的N-甲基吲哚1b-h和吲哚（1 i）与2a有效地反应，在48-91中得到相应的吲哚衍生物3b-h和M。72%的收益率。结果表明，含供电子取代基的N-甲基吲哚比含吸电子取代基的N-甲基吲哚反应活性更高，产物收率更高。同样地，各种取代的丁-3-炔-1-醇2b-e和其它较长链炔基醇2f-i也与N-甲基吲哚（1a）进行环化-加成反应，以良好至优异的产率提供相应的环化-加成产物3 j-m和3a、3 j和3 n-o。本发明的铂催化环化加成反应可以进一步扩展到N-甲基吡咯。从机理上讲，催化反应通过炔醇的分子内氢烷氧基化进行，得到环状烯醇醚，然后将吲哚的C-H键加成到环状烯醇醚的不饱和部分上，得到最终产物。实验证据支持这一建议的机制。
PtCl2 effectively catalyzes the multistep reaction of N-methyl indole (1a) with pent-3-yn-1-ol (2a) in THF at room temperature for 2 It to give indole derivative 3a, which contains a five-membered cyclic ether group at C3 in 93% yield. Under similar reaction conditions, various substituted N-methyl indoles 1b-h and indole (1i) reacted efficiently with 2a to afford the corresponding indole derivatives 3b-h and M in 48-91. and 72% yields. The results showed that N-methyl indoles with electron-donating substituents were more reactive affording higher product yields than those with electron-withdrawing groups. Likewise, various substituted but-3-yn-1-ols 2b-e and other longer chain alkynyl alcohols 2f-i also underwent a cyclization-addition reaction with N-methyl indole (1a) to provide the corresponding cyclization-addition products 3j-m and 3a, 3j, and 3n-o in good to excellent yields. The present platinum-catalyzed cyclization-addition reaction can be further extended into N-methyl pyrrole. Mechanistically, the catalytic reaction proceeds by an intramolecular hydroalkoxylation of alkynyl alcohol to afford cyclic enol ether followed by the addition of the C-H bond of indole to the unsaturated moiety of cyclic enol ether providing the final product. Experimental evidence to support this proposed mechanism is provided.