Oxazoles, 2-alkyl-4,5«dihydro preparation

Similar alkylations may be effected on oxygen. l-(2-Chloroethyl)imidazolidin-2-one (312) when treated with potassium hydroxide or sodium hydride underwent ring closure to the tetrahydroimidazo[2,l-6]oxazole (313) (57JA5276). This approach can be used for the preparation of bicyclic hydantoins and the corresponding dihydro derivatives of (313) using the mesylate of (312) and NaH (77JHC5U, 79JMC1030). 

Each desired enantiomer of 3-substituted dihydro-2(3.//)-furanones and 3-substituted tetrahydro-2//-pyran-2-ones was prepared starting either from 4,5-dihydro-2-(m-trimethylsilyloxy)oxazoles and alkylating with the corresponding alkyl halide, or by reversing the order of alkyl group introduction. Upon hydrolysis with dilute hydrochloric or sulfuric acid, 2-substituted cyclic lactones were obtained in 40-75% overall yield and 60-86% enantiomeric excess20. 

Treatment of aromatic carboxaldehyde (diaminomethylene)hydrazones (105) with hot acetic anhydride or benzoyl chloride affords l,4-diacyl-3-acylamino-5-ary 1-4,5-dihydro- 1H-1,2,4-traizoles (106) in 75-95% yields. In contrast, when the 4-pyridine analog of 105 was employed, the unusual hemianimal triazole derivative (107) was obtained. The structures of the novel compounds were determined by spectral methods and in several cases by x-ray structural analysis. Mechanistic considerations are discussed [95M733]. The oxazole-1,2,4-triazole (108) was prepared by cyclization of the corresponding oxazolecarbonyl-thiosemicarbazide with bicarbonate, alkylation at the sulfur and oxidation to the sulfoxide with MCPBA [95JHC1235]. 

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