S. G. Pil'o

Synthesis of New 5-Mercapto-1,3-oxazole Derivatives on the Basis of 2-Acylamino-3,3-dichloroacrylonitriles and Their Analogs

Enamides of the general formula Cl2CÍC(X)NHCOR1, where X = CN, COOAlk, CONH2, P(O)(OEt)2, P(O)Ph2, +PPh3 Cl-, were treated in succession with alkane- or arenethiols and silver carbonate to obtain 5-alkyl(aryl)thio-2-R1-4-X-1,3-oxazoles with high selectivity. The latter were converted into the corresponding sulfonyl derivatives. Unlike 2-acylamino-3,3-dichloroacrylonitriles which react with sodium hydrogen sulfide in a nonselective fashion, reactions of derivatives like Cl(ArS)CÍC(CN)NHCOR1 with NaHS lead to hitherto unknown 5-arylthio-4-thiocarbamoyl-2-R1-1,3-oxazoles whose structure was confirmed both by spectral methods and by cyclocondensation with bromoacetophenone according to Hantzsch. Heating of some 2-aryl-5-mercapto-4-X-1,3-oxazoles with benzenethiols results in recyclization into the corresponding 2,4-disubstituted 5-arylthio-1,3-thiazoles, presumably due to prototropic tautomerism in the 5-mercaptooxazole fragment.

Recyclization of 2-Aryl-4-cyano-5-hydrazinooxazoles

The available 2-benzoylamino-3,3-dichloroacrylonitrile and its analogs when treated with excess hydrazine hydrate convert to 2-aryl-4-cyano-5-hydrazinooxazoles. The products are fairly stable in usual conditions but undergo recyclization on heating in acetic acid to give previously unknown derivatives of 2-methyl-1,3,4-oxadiazole with a 5-acylamino(carbamoyl)methyl substituent, whose structure was established by spectroscopy and X-ray diffraction. An important role in this complex transformation is probably played by prototropic forms of 4-cyano-5-hydrazinooxazoles, viz. hydrazones of substituted 2-oxazolin-5-ones which are not aromatic and thus can be cleaved with acetic acid and then recyclize.

Reaction of 3,3-Dichloro-2-dichloroacetylaminoacrylonitrile with Amines

Polychlorinated enamidonitrile Cl2CÍC(CN)NHCOCHCl2 readily reacts with primary aromatic amines, dialkylamines, piperidine, and morpholine. The reaction is accompanied by complete elimination of chlorine atoms as chloride ions with formation of 4-cyanooxazoles having the corresponding amine residue in position 5 of the ring and a CHÍN or diaminomethyl moiety in position 2. The structure of 5-arylamino(dialkylamino)-4-cyano-2-formyloxazoles was confirmed by their acid hydrolysis, as well as by the condensation with phenylhydrazine, N-alkylrhodanines, and ethyl acetoacetate in the presence of urea.

Synthesis and Transformations of 4-Phosphorylated 2-Alkyl(aryl)-5-hydrazinooxazoles

Treatment of 1-phosphorylated 2,2-dichloroethenylcarboxamides with excess hydrazine hydrate gives in high yields phosphorylated derivatives of 2-alkyl(aryl)-5-hydrazinooxazoles containing the P(O)(OCH3)2, P(O)(OC2H5)2, and P+(C6H5)3ClO4- groups in the 4-position of the ring. The presence of the hydrazine group in these oxazole derivatives was confirmed not only by the spectral data, but also by the reactions with p-toluic aldehyde, p-toluic chloride, and phenyl isothiocyanate.

Synthesis and Transformations of Two Types of 4-Phosphorylated Aldehydes of the Oxazole Series

Available N-(1,2,2,2-tetrachloroethyl)dichloroacetamide selectively reacts with trialkyl phosphites and triphenylphosphine, which was used for preparing polycentered electrophilic agents unusually reacting with piperidine and morpholine in the presence of water to give in high yields 4-dialkoxyphosphoryl- or 4-triphenylphosphonio-substituted oxazole-2-carbaldehydes containing piperidine or morpholine moiety in the 5-position. Their structure was determined by spectroscopy and also by chemical transformations into phenylhydrazones, thiosemicarbazones, aminals, and other functional derivatives of these two types of phosphorus-containing aldehydes of the oxazole series.