Synthesis of benzoxazoles from imino esters I. 2-Alkyl(aryl)-substituted benzoxazoles

It is found that condensation of esters of iminocarboxylic and iminoperfluorocarboxylic acids with o-aminophenol is a convenient general method for preparing 2-alkyl, 2-perfluoroalkyl, and 2-aryl substituted benzoxazoles. Hydrochlorides of esters of iminocarboxylic acids react smoothly with o-aminophenol even at room temperature. Condensation of esters of iminoperfluorocarboxylic acids, whose hydrochlorides are unstable, is suitably carried out in the presence of an equimolecular quantity of the corresponding perfluorocarboxylic acid. 2-Alkyl(aryl) substituted benzoxazoles can also be obtained by heating o-aminophenol with esters of iminocarboxylic acids in the form of free bases. Esters of iminoperfluorocarboxylic acids also react similarly. Under similar conditions diesters of bisiminocarboxylic and bisiminoperfluorocarboxylic acids and o-aminophenol give, -di(benzoxazolyl-2) alkanes, and, -di(benzoxazolyl-2) perfluoroalkanes respectively.The synthetic part of the work was communicated at the conference on Heterocycles in Organic Synthesis, Kiev, June 1964. For a preliminary communication see [1].     

Synthesis of 2- and 2,5-substituted benzoxazoles and benzothiazoles

A number of 2- and 2,5-perfluoroalkyl and perfluoroalkylether substituted benzoxazoles and benzothiazoles have been prepared. Their relative hydrolytic stability has been examined. In all cases the benzothiazoles were more stable that the benzoxazoles. Substituents in the 2-position offering steric hindrance improve hydrolytic stability.     

Synthesis of benzoxazoles from imino esters I. 2-Alkyl(aryl)-substituted benzoxazoles

It is found that condensation of esters of iminocarboxylic and iminoperfluorocarboxylic acids with o-aminophenol is a convenient general method for preparing 2-alkyl, 2-perfluoroalkyl, and 2-aryl substituted benzoxazoles. Hydrochlorides of esters of iminocarboxylic acids react smoothly with o-aminophenol even at room temperature. Condensation of esters of iminoperfluorocarboxylic acids, whose hydrochlorides are unstable, is suitably carried out in the presence of an equimolecular quantity of the corresponding perfluorocarboxylic acid. 2-Alkyl(aryl) substituted benzoxazoles can also be obtained by heating o-aminophenol with esters of iminocarboxylic acids in the form of free bases. Esters of iminoperfluorocarboxylic acids also react similarly. Under similar conditions diesters of bisiminocarboxylic and bisiminoperfluorocarboxylic acids and o-aminophenol giveα, ω-di(benzoxazolyl-2) alkanes, andα, ω-di(benzoxazolyl-2) perfluoroalkanes respectively.     

Liquid-phase synthesis of 2-substituted benzimidazoles, benzoxazoles and benzothiazoles

A novel acid fluoride for use in the liquid-phase synthesis of substituted benzimidazoles, benzoxazoles and benzothiazoles was developed. Its synthetic utility is exemplified by a structurally diverse set of aromatic heterocycles. Final cleavage is achieved by treatment with sodium methoxide in methanol for 12 h. The corresponding benzimidazoles, benzoxazoles and benzothiazoles were obtained in good isolated yields (22-62%, four steps).     

Synthesis and optical properties of 5-substituted 2-(2-tosylaminophenyl)benzoxazoles

Various 5-substituted 2-(2-tosylaminophenyl)benzoxazoles were synthesized. The presence of intramolecular hydrogen bonding, the strength of which depends on the nature of the substituent, was shown by means of the IR spectra of the investigated series of compounds. A correlation between v _NH and the Taft substituent constants was found. The investigated benzoxazoles have fluorescence in the yellow-green region of the spectrum; an anomalously large Stokes shift is characteristic for them. The position of the fluorescence spectrum depends on the strength of the hydrogen bond: when it becomes weaker, the spectrum is shifted bathochromically.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 472–478, April, 1973.     

Cyclization Studies with N-Mannich bases of 2-substituted indoles

The synthesis of the indoles 7 , 15 , 16 with a 3-methoxyphenyl group, attached via an α-side chain of 1,2,or 3 CH₂ units, is reported. These compounds, after appropriate protection at C(3), were transformed into the N-[(dimethylamino)methyl]indoles 22 , 23 , and 24 , respectively. When treated with AcCl, these N-Mannich bases gave, in two cases, stable N-(chloromethyl)indoles 25 and 26 . In the presence of SnCl₄, ring closure occurred via electrophilic attack of 1-methylideneindolium ions on the methoxyphenyl group. Formation of seven-membered rings (→ 27 , 28 ) and eight-membered rings (→ 29 ) was found to be a favorable process. Cyclization to six-membered rings did not occur within this series.     

Synthesis of 6-substituted 2-pyrrolyl and indolyl benzoxazoles by intramolecular O-arylation in photostimulated reactions

The synthesis of a series of 6-substituted 2-pyrrolyl and 2-indolyl benzoxazoles by photostimulated C-O cyclization of anions from 2-pyrrole carboxamides, 2-indole carboxamides, or 3-indole carboxamides has been found to proceed in good to excellent yields (41-100%) in DMSO and liquid ammonia. The pyrrole and indole carboxamides are obtained in good to very good isolated yields by an amidation reaction of different 2-haloanilines with 2-carboxylic acid of pyrrole and 2- or 3-carboxylic acid of indole. To explain the regiochemical outcome of these reactions (C-O arylation vs C-N or C-C arylation), a theoretical analysis was performed using DFT methods and the B3LYP functional.     

Synthesis and properties of furan derivatives. 5. Synthesis of 2-substituted benzoxazoles containing furan fragments

The condensation of imidates and imidate hydrochlorides of furan acids with o-aminophenols gives furyl derivatives of 2-substituted benzoxazoles. Such compounds are also formed in the reaction of furan acids with o-aminophenol in the presence of boric acid.Communication 4, see [1].I. M. Gubkin State Petroleum and Gas Academy, 117917 Moscow. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 896–901, July, 1996. Original article submitted April 16, 1996.     

Synthesis of 2-(3-phenoxyphenyl)-substituted benzoxazoles,based on nitriles containing the diphenyl oxide fragment

A method is proposed for the preparation of 2-(3-phenoxyphenyl)-substituted benzoxazoles, which are of interest as structural blocks for the synthesis of compounds possessing potential biological activity.     

Synthese de F-alkyl-2 benzoxazoles

N-(2-hydroxy phenyl) F-alkylamides obtained by the action of F-acyl chlorides with various substituted 2-aminophenols led by distillation over phosphoric anhydride to substituted 2-F-alkyl benzoxazoles. This method gave improved results compared with the existing processes in the literature. The results are discussed with respect to different structural characteristics such as the nature of the benzene substituents, the length of the F-alkyl chain, etc.     

Oxidative cyclization of thiophenolic and phenolic Schiff's bases promoted by PCC: a new oxidant for 2-substituted benzothiazoles and benzoxazoles

Pyridinium chlorochromate (PCC) supported on silica gel effects the oxidative cyclization of structurally diverse thiophenolic and phenolic Schiff's bases, thereby providing an efficient and convenient method for the synthesis of a library of 2-arylbenzothiazoles and 2-arylbenzoxazoles.     

Iron-catalyzed intramolecular o-arylation: synthesis of 2-aryl benzoxazoles

A practical iron-catalyzed intramolecular O-arylation reaction and its application in the synthesis of benzoxazole derivatives, starting from the readily available 2-haloanilines, is presented. The key cyclization step involves the use of a combination of the cheap and environmentally friendly FeCl(3) and 2,2,6,6-tetramethyl-3,5 heptanedione (TMHD) as the catalyst system.     

化学修饰在质谱中的应用 3: 环丙烷脂肪酸的苯并 唑衍生物的质谱特征

本文作者曾成功地利用苯并 唑衍生物直接鉴定出不饱和脂肪酸中酸双键位置。本文在该基础上继续研究了长链环丙烷酸的苯并 唑衍生物的质谱, 结果证明脂肪链上的环丙烷基部位在其质谱上可得到特征的反映, 根据谱中碳链系列离子峰的质量间隔, 就可确定出环丙烷基在脂肪链的位置。     

Tandem migration-carboalkoxylation of o-isocyanophenyl acetals leading to benzoxazoles

An efficient approach to benzoxazoles via tandem migration-carboalkoxylation of o-isocyanophenyl acetals has been developed. Both a Lewis acid and base are essential for this reaction, and the BF(3)·OEt(2)/2,4,6-collidine combination is the best choice for cooperative transformation.     

可见光诱导邻烯基甲酰苯胺环化合成2-喹啉酮

使用廉价易得的邻烯基甲酰苯胺在可见光的诱导下发生自由基环化反应, 以良好至优秀的产率合成了15种2-喹啉酮衍生物. 该方法简单高效、 条件温和、 产率较高, 具有优异的官能团兼容性, 不仅拓展了邻烯基甲酰苯胺参与的新型有机反应, 也为光催化合成喹啉酮类化合物提供了一条新途径.     

Transcyclization of benzoxazoles

The reaction of benzoxazoles with aromatic and aliphatic acids, which gives transcyclization products — 2-substituted benzoxazoles — was studied. The reaction of 2-hydroxyacetanilide with aliphatic acids gives a mixture of 2-substituted benzoxazoles. Under similar conditions, 2-methylbenzothiazole, 2-alkyl-²-oxazolines, and 2-alkyl-²-thiazolines do not undergo transcyclization, but ring opening is observed in the latter two cases.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1480–1482, November, 1972.