2,1-Bensoidoxazoles [anthranils]. Synthesis and opening of the isoxazole ring (review)
The present review covers the literature on the synthesis of 2,l-benzoisoxazoles (anthranils) (I), and reactions of this bicyclic system which involve opening of the isoxazole ring. Since a detailed and satisfactorily full review of the chemistry of 2, l-benzoisoxazoles was published in 1967 [96], the main thrust of the present review is to cover the literature of the last twenty years. It has nevertheless been necessary to include earlier publications, especially when these deal with general methods of synthesis of anthranils. t i. Synthesis of 2~l-Benzisoxazoles
Ring opening reactions of 6H‐anthra[1,9‐cd]isoxazol‐6‐ones and related compounds
Nucleophilic attack of anthra[1,9-cd]isoxazol-6-ones, and of anthra[1,9-cd:5,10-c'd']isoxazole by various sulfoxides, triphenyl phosphine, and aliphatic or aromatic phosphites proceeded with cleavage of the nitrogenoxygen bond of the isoxazole ring. This method provided ready access to substituted anthraquinones bearing sulfoximido-, triphenylphosphazo-, and dialkyl(aryl)phosphoramidic groups attached to the 1- and the 1,5-positions of the anthraquinone system. The structures of the newly synthesized anthraquinone derivatives were supported by analytical and spectral data. l-S,S-dimethyl-N-(5-benzamidoanthraquinon-1-yl)-sulfoximide yielded in 90% sulfuric acid the l-amino-5-sulfoximido anthraquinone without hydrolyzing the sulfoximido group.
Studies in azide chemistry. Part V. Synthesis of 4-azido-2,3,5,6-tetrafluoro-, 4-azido-3-chloro-2,5,6-trifluoro-, and 4-azido-3,5-dichloro-2,6-difluoro-pyridine, and some thermal reactions of the tetrafluoro-compound
4-Azido-2,3,5,6-tetrafluoropyridine can be prepared by nitrosation of 2,3,5,6-tetrafluoro-4-hydrazinopyridine or, preferably, treatment of pentafluoropyridine with sodium azide in acetonitrile, a reagent that converts 3-chloro-2,4,5,6-tetrafluoro- and 3,5-dichloro-2,4,6-trifluoro-pyridine into 4-azido-3-chloro-2,5,6-trifluoro- and 4-azido-3,5-dichloro-2,6-difluoro-pyridine, respectively. 4-Azido-2,3,5,6-tetrafluoropyridine decomposes smoothly into nitrogen and an intractable solid at temperatures above ca. 130 °C, undergoes the Staudinger reaction with tri-phenylphosphine at room temperature, reacts with dimethyl sulphoxide at elevated temperatures to give a sulphoximide, partakes in 1,3-dipolar cycloaddition reactions with benzyne, diphenylacetylene, phenylacetylene, cyclopentadiene dimer, and norbornene, yields 4-anilino-2,3,5,6-tetrafluoropyridine with benzene at 175 °C, and reacts with cyclohexane to give the C–H ‘insertion’ product 4-(cyclohexylamino)-2,3,5,6-tetrafluoropyridine and 4-amino-2,3,5,6-tetrafluoropyridine. Thermal decomposition of the azide in a mixture of cyclo-hexane, -heptane, and -octane reveals that C–H ‘insertion’ is encouraged by increase in ring size, and thermolysis experiments with cis- and trans-1,2-dimethylcyclohexane show that this type of reaction lacks stereospecificity. The results of reactions between the azide and trans-4-methylpent-2-ene at elevated temperatures indicate that 1,3-dipolar cycloaddition occurs before nitrene generation can be achieved. Authentic samples of the new amino-pyridines [PhNHpyF, cyclo-CnH2n–1·NHpyF(n= 6, 7, or 8), cis- and trans-cyclo-1,2-Me2C6H9·NHpyF, and cis- and trans-Pri[graphic omitted]pyF(pyF= 2,3,5,6-tetrafluoro-4-pyridyl)] encountered in this work can be obtained via nucleophilic attack by the appropriate amines on pentafluoropyridine.