The oxidation of o‐alkynylarenecarbaldehydes into tricarbonyl compounds by an iodine/water system is described. The reaction takes place via isochromenol intermediates formed by intramolecular assistance of the formyl group. The procedure was applied to various o‐alkynylarenecarbaldehydes to afford the corresponding products in good to excellent yields.
A facile iodine/water‐mediated oxidation of the triple bond of o‐alkynylaroyl compounds to furnish tricarbonyl compounds is reported. The reaction proceeds through the formation of isochromenol intermediates by the assistance of the neighbouring aroyl group. The product tricarbonyl compounds are versatile synthetic precursors that, upon treatment with mono‐ and diamines, hydrazines and amino alcohols, afford various heterocyclic scaffolds such as isoindolinones, phthalazines, benzimidazoisoquinolinones, quinoxalines and benzimidazole‐quinoxaline hybrid compounds. Mechanistic aspects of the formation of the above heterocycles are discussed. Finally, a short synthetic route to the isoindolinone natural product, aristolactam BII is reported.
Indium(III) triflate is found to be an effective catalyst for the benzannulation reactions of o-alkynylbenzaldehydes with enolisable aldehydes, ketones, 1,3-diketones and β-keto esters. The reactions produce naphthyl ketones through ring opening of adducts arising from the inverse electron demand Diels-Alder reactions between in situ generated isochromenylium cations and enols. The main feature of the method is selective formation of naphthyl ketones in a highly regioselective manner without any decarbonylation.
The action of a Reformatsky reagent on o-alkynylarenenitriles provides a convenient access to naphthalene amino esters via tandem 6-endo-dig carbannulation of in situ generated Blaise reaction intermediates. The products are formed in moderate to good yields with high chemo- and regioselectivity.
o-Alkynylarenenitriles when heated with Pd(OAc)2/H2O/(±)-CSA in DMSO undergo simultaneous alkyne oxidation and nitrile hydration to give 3-aryl-3-hydroxy-2,3-dihydroazanaphthoquinones. Upon treatment with (±)-CSA, these compounds form 3-arylazanaphthoquinones in situ, which add to electron-rich aromatics and terminal alkene/alkyne to afford 3,3-disubstituted-2,3-dihydroazanaphthoquinones.
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