Synthesis of Pyrroles through a 4蟺-Electrocyclic Ring-Closure Reaction of 1-Azapentadienyl Cations

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• 作者：Rishikesh Narayan ; Roland Fr枚hlich ; Ernst-Ulrich W眉rthwein
• 刊名：The Journal of Organic Chemistry
• 出版年：2012
• 出版时间：February 17, 2012
• 年：2012
• 卷：77
• 期：4
• 页码：1868-1879
• 全文大小：465K
• 年卷期：v.77,no.4(February 17, 2012)
• ISSN：1520-6904

文摘

1-Azapenta-1,4-diene-3-ols 4a鈥?b>m are easily accessible from 1-azapenta-1,4-dien-3-ones 3a鈥?b>i and organolithium compounds. Treatment of the compounds 4a鈥?b>m with strong acid (triflic acid) generates 1-azapentadienyl cations in situ upon protonation at the hydroxyl oxygen atom and subsequent water elimination. The intermediate cations undergo facile 4蟺-electrocyclization under ambient condition to give diversely substituted pyrroles 6a鈥?b>m in moderate to good yield. The product pyrrole 6k could be characterized by X-ray diffraction. Quantum chemical calculations were performed to elucidate the mechanism of this reaction with respect to starting compounds, transition states, and products. They support the proposed mechanism of a 4蟺-conrotatory M枚bius-type electrocyclic ring-closure reaction.