Regioselective Syntheses of 2- and 4-Formylpyrido[2,1-b]benzoxazoles

Abstract

o-Acetaminophenols (2) reacted with Vilsmeier reagent under Meth-Cohn conditions to yield 2-formylpyrido[2,1-b]benzoxazoles (5) unexpectedly besides the known compounds 2-(benzoxazol-2'-yl)-3-dimethylaminoacroleins (4). Refluxing 4 in acetic anhydride gave 4-formylpyrido[2,1-b]benzoxazoles (6), an isomer of 5. Both 5a and 6a were structurally characterized by X-ray crystallography. A mechanism for the formation of 5 involving sequential chlorination, dimerization, intramolecular elimination of HCl to form the oxazole ring, formylation twice, and regioselective intramolecular nucleophilic cyclization to construct the pyridone ring is proposed.

K10 montmorillonite clays as environmentally benign catalysts for organic reactions

“…74 Benzoxazole, benzothiazole, oxazolopyridine and imidazopyridine derivatives are prepared from 2-aminophenol, 2-aminothiophenol, o-hydroxyaminopyridine, and 2,3-diaminopyridine as the respective starting precursors. These amines can be coupled with carboxylic acid or carboxylic acid derivatives and followed by dehydration, generally catalyzed by strong acids such as polyphosphoric acid, 75 sulfuric acid, 76 phosphorous oxychloride 77 and Lewis acids. 78 2-Aminophenol or diamine treated with trimethylorthoesters in the presence of an acid catalyst such as sulfuric acid, BF 3 •EtO 2 and hydrochloric acid gave the corresponding benzoxazoles and benzimidazoles.…”

Synthesis, Structural Characterization and Metal Inclusion Properties of 18‐, 20‐ and 22‐Membered Oxaazacyclophanes and Oxaazacalix[4]arene Analogues: Macrocyclic Amine and Schiff Base Receptors with Variable NxOy Donor Sets

“…Treatment of 2-(acetylamino)-phenol (1) with suitable alkyl dihalides in a 2:1 molar ratio gave the corresponding ethers 2-5, which were then deprotected to afford the corresponding diamine derivatives 6-9. Compounds 1-2, 5-7 and 9 had been reported in the literature previously, [29][30][31][32][33][34][35] but the diamines 3, 4 and 8 had not. The dialdehyde building blocks 10-13 were prepared by an analogous Williamson ether synthesis with salicylaldehyde in place of the N-protected amine 1.…”

“…[29] A solution of acetic anhydride (0.11 g, 14.7 mmol) in methanol (3 mL) was added slowly to a suspension of 2-aminophenol (0.70 g, 6.42 mmol) in water (20 mL). The reaction mixture was then stirred for 5 h at room temperature.…”

Method for the Synthesis of Phenothiazines via a Domino Iron-Catalyzed C–S/C–N Cross-Coupling Reaction

“…Given that there are no reports in the literature to date pertaining to the use of iron as a catalyst for the coupling reaction of an arylamine and aryl halide, we used an acyl-protected arylamine to investigate this reaction because it could be readily removed upon completion of the coupling reaction . The reaction of 1a with 1,2-dibromobenzene was used as the model transformation to identify the optimum reaction conditions by screening a variety of different iron salts, bases, ligands and solvents (Table ).…”