Synthesis of functionalised pyrido[4,3-b][1,4]oxazine and imidazo[1,2-a]pyridine derivatives

Design, synthesis, and herbicidal activity of novel 2-(arylamino)-5-methyl-4-methylene-7-(methylthio)-4H-pyrido[4,3-d][1,3]oxazine-8-carbonitrile derivatives

A series of 5-methyl-4-methylene-7-methylthio-2-arylmino-4 H-pyrido[4,3- d][1,3]oxazine-8-carbonitrile derivatives were synthesized via tandem aza-Wittig and annulation reactions with { N-[3-acetyl-5-cyano-2-methyl-6-(methylthio)pyridin-4-yl]imino}triphenylphosphorane and aryl isocyanate in dry dichloromethane. Their structures were clearly confirmed by infrared, 1H NMR, 13C NMR, high-resolution mass spectrometry, and X-ray single-crystal diffraction. All newly synthesized compounds were screened for herbicidal activities against monocotyledonous and dicotyledonous plants. The results indicated that the target compound 2-[(4-methoxyphenyl)amino]-5-methyl-4-methylene-7-(methylthio)-4 H-pyrido[4,3- d][1,3]oxazine-8-carbonitrile showed 100% inhibition rate to grain sorghum (monocotyledonous) at the concentration of 100 mg L−1.

Pd-Catalysed One-Pot Synthesis of 2H-1,4-benzoxazin-3-(4H)-ones from o-halophenols and 2-chloroacetamides

A Pd-catalysed cascade protocol, consisting of intermolecular O-alkylation and spontaneous intramolecular amidation, has been established for efficient synthesis of 2 H-1,4-benzoxazin-3-(4 H)-ones from o-halophenols and 2-chloroacetamides. A varity of substrates afford the desired products in good to excellent yields. It is particularly attractive for synthesis of a library of 2 H-1,4-benzoxazin-3-(4 H)-ones.

A One-Pot Synthesis of Pyrido[2,3-b][1,4]oxazin-2-ones

Pyrido[2,3-b][1,4]oxazin-2-ones are conveniently prepared in excellent yields by a one-pot annulation of N-substituted-2-chloroacetamides with 2-halo-3-hydroxypyridines with use of cesium carbonate in refluxing acetonitrile. The key transformation features a Smiles rearrangement of the initial O-alkylation product and subsequent cyclization.