RESUMO
Hepta-2,3,5-trienedioates 1 have been employed as substrates to explore Lewis base-catalyzed annulation reactions. This leads to the discovery of a phosphine-catalyzed [3+2] annulation of 1 with electron-deficient alkenes for the construction of exocyclic olefinic cyclopentenes in good yields and moderate E:Z ratios under mild conditions. The annulation is believed to proceed in a tandem [3+2] cyclization and double bond migration in which the ε-ester is crucial to both processes. This reaction also showcases a substrate-controlled divergent reactivity compared to that of a previous report.
RESUMO
Herein we describe a catalyst-free regioselective [3 + 3] annulation/oxidation reaction of cyclic amidines such as DBU (1,8-diazabicyclo(5.4.0)undec-7-ene) and DBN (1,5-diazabicyclo(4.3.0)non-5-ene) with activated olefins, i.e., 2-arylidenemalononitriles and 2-cyano-3-aryl acrylates, to afford tricyclic 2-pyridones and pyridin-2(1H)-imines, respectively. The mechanism has been proposed based on DFT calculations. In the reaction, the cyclic amidines serve as C,N-bisnucleophiles for the cyclization, while the olefins play a dual role by acting as both reactants and oxidants.
RESUMO
A three-component reaction between one molecule of phosphorus ylides (P-ylides) and two molecules of isocyanates for the rapid assembly of 2-amino-3-carboxylate-4-quinolones is described. The mechanism may involve the addition of a P-ylide to an isocyanate followed by 1,3-H shift to form a carbamoyl stabilized P-ylide. The intermediate then reacts with another aryl isocyanate via Wittig/ketenimine-ketene rearrangement/6π-electrocyclization/1,3-H shift to finally afford the 4-quinolones.