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Browsing by Author "Lima, Carlos F.R.A.C."

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  • 2-[(1E,3E)-4-Arylbuta-1,3-dien-1-yl]-4H-chromen-4-ones as dienes in Diels-Alder reactions - experimental and computational studies
    Publication . Albuquerque, Hélio; Santos, Clementina M.M.; Lima, Carlos F.R.A.C.; Santos, Luís M.N.B.F.; Cavaleiro, José; Silva, Artur
    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, :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.
    2017Journal article Open access Show more
  • 2-[(1E,3E)-4-Arylbuta-1,3-dien-1-yl]-4H-chromen-4-ones as dienes in Diels–Alder reactions: experimental and computational studies
    Publication . Albuquerque, Hélio; Santos, Clementina M.M.; Lima, Carlos F.R.A.C.; Santos, Luís M.N.B.F.; Cavaleiro, José; Silva, Artur
    The synthesis and reactivity of 2-[(1 £,3£)-4-arylbuta-1 ,3-dien-l-yl]-4H-chromen-4-ones 1 as dienes in Diets-Alder (DA) reactions towards several electron-poor and electron-rich dienophiles under microwave irradiation was studied. The optimized reaction conditions were achieved by using N-methylmaleimide2 as dienophile and Sc(0Tf)3 as Lewis acid under microwave-assisted and solvent-free conditions. The Lewis acid improved the reaction yields since it prevented the adducts obtained to undergo a second DA reaction, thus avoiding formation of a bisadduct. The a,~:y ,o-diene of the starting chromones showed to be the most reactive and the computational results confirmed the experimental findings. Theoretical calculations also allowed explaining some unexpected lack of reactivity by some dienophiles. The adducts prepared were dehydrogenated by using DDQ, however, the aza-adducts showed to be sensitive to the high energetic reaction conditions necessary to perform the aromatization.
    2016Conference object Open access Show more