Pd catalyzed couplings of “superactive esters” and terminal alkynes: Application to flavones and γ-benzopyranones construction

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• 作者：Dandan Yang ; Zhenhua Wang ; Xiu Wang ; Huaming Sun ; Zunyuan Xie ; Juan Fan ; Guofang Zhang ; Weiqiang Zhang ; ^{zwq@snnu.edu.cn} ; Ziwei Gao ; ^{zwgao@snnu.edu.cn}
• 关键词：Palladium catalyzed alkynlation ; 1 ; 3-Ynones ; 6-Endo cyclization ; Flavones ; γ-Benzopyranones
• 刊名：Journal of Molecular Catalysis A: Chemical
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：426
• 期：part_PA
• 页码：24-29
• 全文大小：1858 K
• 卷排序：426

文摘

The flavones and γ-benzopyranones represent one of the most prevalent structural heterocycles in natural products. In this manuscript, the diversity oriented synthesis of the flavones and γ-benzopyranones was accomplished by palladium catalyzed Sonogashira coupling reactions of o-acylated salicacly acid triazine esters and terminal alkynes, and sequentially, piperidine catalyzed 6-endo cyclization. N-Methylmorpholine (NMM) significantly accelerated Pd catalyzed cross-coupling of the steric hindrined triazine esters and terminal alkynes with high efficiency and regioselectivity. The new Pd/NMM catalyst system showed excellent functional groups tolerance for 24 examples of acylated o-alkynoylphenols derivatives. The mechanistic experiments clearly demonstrated that NNM stabilized the catalytic palladium species, and promoted the leaving of triazine moiety during the catalytic cycle. Under very mild condition, piperazine efficiently catalyzed 6-endo cyclization of the acylated o-alkynoylphenols derivatives, affording 24 examples of γ-benzopyranones with excellent yields.