2-[(1E,3E)-4-Arylbuta-1,3-dien-1-yl]-4H-chromen-4-ones as dienes in Diels–Alder reactions: experimental and computational studies
Conference Paper
Overview
Overview
abstract
Thanks are due to University of Aveiro and FCT/MEC for the financial support of the QOPNA research unit (FCT UID/QUI/00062/2013) and CIQ-UP (Pest-C/QUI/UI0081/2013) through national founds and, where applicable, co-financed by the FEDER, within the PT2020 Partnership Agreement, and to the Portuguese NMR Network, as well as to the Instituto Politécnico de Bragança. H.M.T.A. and C.F.R.A.C.L. are grateful to FCT for their PhD (SFRH/BD/86277/2012) and Post-doc (SFRH/BPD/77972/2011) grants,
respectively.
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.
