A regioselective [3+2] cycloaddition (32CA) reaction to synthesize unsymmetric spiro-barbituric pyrazolines containing a chromone or phenolic pyrazole moiety was achieved, providing good to excellent yields.
A convenient regio- and diastereoselective synthesis of functionalized 5a,5b-dihydro-5H,13H-naphtho[1′′,8′′:4′,5′,6′]pentaleno[1′:3,4]pyrrolo[2,1-a]isoquinolin-5-ones via 1,3-dipolar cycloaddition reaction of 8H-cyclopenta[a]acenaphthylen-8-ones with carbonyl-stabilized isoquinolinium N-ylides, is described. Based on DFT calculations at b3lyp/6-311+g(d,p) level of theory, a nonconcerted mechanism is proposed to explain the regioselectivity of this reaction. The structure of a typical product was confirmed by X-ray crystallographic analysis.
A convenient and novel 1,3-dimethylbarbituric acid-mediated methodology for constructing diverse benzimidazole-fused heteroaromatics has been developed. This metal-free cascade annulation of readily available 3-formylchromones, 1,2-diaminoarenes, and cyclic 1,3-dicarbonyl compounds provides an alternative synthetic route in the green conditions. 1,3-Dimeth-ylbarbituric acid acts as a protecting group and accelerates intramolecular cyclization. This one-pot protocol proceeds through cascade nucleophilic addition, ring-opening, Michaeltype addition, intramolecular cyclization, elimination, and air oxidation reactions.
A piperidine-catalyzed reaction between 3-formylchromone, 1,3-dimethyl barbituric acid, and ylidenemalononitriles is developed that offers chromonyl diene products in good yields.
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