Chromone derivatives as novel dienes in Diels-Alder reactions Conference Paper uri icon


  • Chromones are a group of heterocyclic compounds widespread in Nature and an interesting scaffold because they have been involved in a range of chemical transformations [1]. Following our previous studies on Diels‒Alder (DA) reactions of chromone derivatives [2], novel 2-[(1E,3E)-4-arylbuta-1,3-dien- 1-yl]-4H-chromen-4-ones 1 were synthesized to further study the reactivity of their two diene systems (α,β:γ,δ versus 2,3:α,β) in DA reactions (Fig.1). A series of dienophiles were reacted with chromones 1 under microwave-assisted conditions. The best yields of adducts 2 were achieved using N-methylmaleimide as dienophile and Sc(OTf)3 as Lewis acid in solvent-free conditions. The crucial role of Sc(OTf)3 relies on the chelation with carbonyl group of adducts 2 avoiding both the occurrence of a second DA reaction and the formation of bisadducts 6. The α,β:γ,δ-diunsaturated system of chromones 1 showed to be the most reactive diene for maleimides, dicarboxylates and azo-dicarboxylates, affording adducts 2, 4 and 5, respectively. Adducts 2 were dehydrogenated to the corresponding flavone derivatives 3 using DDQ as oxidizing agent (Fig.1). Computational calculations confirmed the experimental findings on DA reactions and helped to explain the unexpected lack of reactivity of some dienophiles. All the experimental procedures and extensive 1D and 2D NMR characterization of the final adducts and intermediates will be presented and discussed.
  • 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, cofinanced 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.

publication date

  • January 1, 2016