Albuquerque, HélioSantos, Clementina M.M.Lima, Carlos F.R.A.C.Santos, Luís M.N.B.F.Cavaleiro, JoséSilva, Artur2017-09-222017-09-222017Albuquerque, Hélio; Santos, Clementina M.M.; Lima, Carlos F.R.A.C.; Santos, Luís M.N.B.F.; Cavaleiro, José; Silva, Artur (2017). 2-[(1E,3E)-4-Arylbuta-1,3-dien-1-yl]-4H-chromen-4-ones as dienes in Diels-Alder reactions - experimental and computational studies. European Journal of Organic Chemistry. ISSN 1434-193X. 1, p. 87–1011434-193Xhttp://hdl.handle.net/10198/14518The 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.engjournal article10.1002/ejoc.201601072