2-[(1E,3E)-4-Arylbuta-1,3-dien-1-yl]-4H-chromen-4-ones as Dienes in Diels-Alder Reactions - Experimental and Computational Studies
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- 作者：Hé ; lio M. T. Albuquerque ; Clementina M. M. Santos ; Carlos F. R. A. C. Lima ; Luí ; s M. N. B. F. Santos ; José ; A. S. Cavaleiro and Artur M. S. Silva
- 刊名：European Journal of Organic Chemistry
- 出版年：2017
- 出版时间：January 3, 2017
- 年：2017
- 卷：2017
- 期：1
- 页码：87-101
- 全文大小：1850K
- ISSN：1099-0690
文摘
The synthesis and reactivity of 2-[(1E,3E)-4-arylbuta-1,3-dien-1-yl]-4H-chromen-4-ones as dienes in Diels–Alder (DA) reactions with several electron-poor and electron-rich dienophiles under microwave irradiation was studied. The optimized reaction conditions were achieved with N-methylmaleimide as the dienophile and Sc(OTf)3 (OTf = triflate) as a Lewis acid under microwave-assisted and solvent-free conditions. The Lewis acid improved the reaction yields as it prevented the adducts obtained from undergoing a second DA reaction; thus, the formation of a bisadduct was avoided. The α,β:γ,δ-diene of the starting chromones was the most reactive, and the computational results confirmed the experimental findings. Theoretical calculations also provided a rationale for the unexpected lack of reactivity shown by some dienophiles. The adducts prepared were dehydrogenated with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ); however, the aza adducts were sensitive to the highly energetic reaction conditions necessary for the aromatization.