A variety of 2‐halo‐5‐thiazolecarboxylates was prepared from substituted‐3‐aminoacrylates and 3‐ketoes‐ters. Selective reduction of 2‐chloro‐5‐thiazolecarboxylates 4a, 4i and 4j with sodium borohydride in ethanol provided the corresponding 2‐halo‐5‐thiazolemethanols 27‐29. Nucleophilic displacements on [2‐chloro‐4‐(trifluoromethyl)‐5‐thiazolyl]methyl methanesulfonate (32c) occurred selectively at the 5‐substituent to provide 2‐chloro‐4‐(trifluoromethyl)‐5‐(heteroatom‐substituted‐methyl)thiazoles 32d‐f.
Reaction of ethyl 4,4,4‐trifluoroacetoacetate with methylhydrazine produced not only the previously reported 5‐hydroxy‐3‐(trifluoromethyl)pyrazole 1 but also its unknown isomer the 3‐hydroxy‐5‐(trifluoromethyl)pyrazole 4. The structure assignments are established based on 13C nmr spectra. Compound 1 was converted to 5‐chloro‐3‐(trifluoromethyl)pyrazolecarboxylic acid 3 in two steps.
Cycloaddition of aromatic nitrile oxides to methyl o‐vinylbenzoate produced methyl 2‐(3‐aryl‐2‐isoxazolin‐5‐yl)benzoates; the isoxazolines were converted to methyl 2‐(3‐arylisoxazol‐5‐yl)benzoates. Reaction of the nitrile oxide from o‐methoxycarbonylbenzohydroximinoyl chloride (11) with phenylacetylene, styrenes, and aromatic nitriles resulted in methyl 2‐(5‐phenylisoxazol‐3‐yl)benzoate, methyl 2‐(5‐aryl‐2‐isoxazolin‐3‐yl)‐benzoates (15), and methyl 2‐(5‐aryl‐1,2,4‐oxadiazol‐3‐yl)benzoates, respectively. The isoxazolines 15 were converted to the corresponding isoxazoles 16.
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