Eine einfache Synthese von Isoxazol-5-carbonsäure

Efficient synthesis and dehydration reaction of trichloromethylated 2‐(3‐phenyl‐5‐hydroxy‐4,5‐dihydro‐1H‐pyrazol‐1‐yl)‐4‐aryl‐5‐alkylthiazoles

“…In contrast with compound 1, compound 4 does not show the thioamide bond at N-1, and the new bond between the heterocycles 3 is extremely strong and allows the dehydration reaction in sulfuric acid medium. It is interesting that the CCl 3 substituent was not converted into carboxyl group, in contrast to the dehydration reaction described by Spiegler [7], which obtained isoxazole-5-carboxylic acid from the reaction of 5-trichloromethylisoxazole with 96% sulfuric acid at 110…”

“…For example, trichloromethyl substituted benzodiazepines [2,3], 4,5-dihydro-pyrazoles [4], and quinazolines [5] have exhibited activity as acetylcholinesterase and ATPDase inhibitors [2], anxiolytics [3], antiinflammatories [4], analgesics [4], and cyclindependent kinases (CDKs) inhibitors [5] in the cell cycle proteins. Thus, the possibility to obtain trichloromethyl-substituted heterocycles [6][7][8] combined with the versatility of the trichloromethyl group as precursor of carboxyl groups [9][10][11], prompted us to devote special attention to the chemistry of the trichloromethyl-contained building blocks. Although many methods for the synthesis of thiazoles and pyrazoles have been reported [12][13][14][15][16][17][18], the synthesis of noncondensed 5,5-bicycles, as 2-(1H-pyrazol-1-yl)-thiazoles, was little explored.…”

“…This approach relies on the trichloroacetylation of enol ethers or acetals to give, in one step and good yields, ␤-alkoxyvinyl trichloromethyl ketones, which proved to be useful building blocks for the synthesis of five [7,[24][25][26][27], six [8,[28][29][30], and seven [9,31] membered trichloromethylated heterocyclic compounds.…”

Regiospecific synthesis of 1,2-bis(azolyl)ethanes

“…The mild reaction condition used for the synthesis of 1,2-bis(isoxazolyl)ethanes 3-6 was appropriate to preserve the trichloromethyl group on the heterocycle and to define the regiochemistry of the cyclocondensation. 16,17 The structure of 4,5-dihydroisoxazole was evidenced by the presence of two doublets in the 1 H NMR spectrum in the range of δ 3.10 to 3.70 assigned to H4'a e H4'b. The observation of a peak around δ 47.0 in the 13 C NMR spectrum from methylene C4', further confirmed the structure of 4,5-dihydroisoxazoles 3 and 4 (Table 3).…”

“…Tetrahydropyrrolo [1,5-b] pyrazole (16) Hydrazine hydrate (2.1 mmol) was added drop wise at room temperature to a stirred solution of 1,1,1,10,10,10-hexachloro-4,7-dimethoxydeca-3,7-dien-2,9-dione (2) (2 mmol) in acetonitrile (20 mL). The mixture was stirred for 4 hours at room temperature.…”