Synthesis, structure and properties of N-acetylated derivatives of methyl 5-amino-1H-[1,2,4]triazole-3-carboxylate.
Methyl 5-amino-1H-[1,2,4]triazole-3-carboxylate hydrochloride (1). and free ester (2). were obtained and 2 was reacted with Ac(2)O to give the acetylated products 3-6. Compounds 1-6 were studied using HPLC, GC-MS, FTIR and multinuclear NMR spectroscopy, including the cross-polarisation magic angle spinning (CPMAS) technique. The results of the acetylation of 2 were compared to those of the acetylation of 5-amino-1H-[1,2,4]triazole, and for 2 a significant decrease in the susceptibility to acetylation was found. The reaction of 2 with Ac(2)O at 20 degrees C, regardless of the amount and the concentration of the latter, including neat Ac(2)O, proceeds fully regioselectively and leads to one product: methyl 1-acetyl-5-amino-1H-[1,2,4]triazole-3-carboxylate (3). In sharp contrast to 5-amino-1H-[1,2,4]triazole, neither an additional monoacetylated isomer, whether annular or exocyclic, nor any diacetylated derivative could be detected. The diacetylation of 2 requires the process to be carried out in neat boiling Ac(2)O and, as in the case of 5-amino-1H-[1,2,4]triazole, gives two diacetylated isomers. These are methyl 1-acetyl-3-(acetylamino)-1H-[1,2,4]triazole-5-carboxylate (4) and 1-acetyl-5-(acetylamino)-1H-[1,2,4]triazole-3-carboxylate (5). Hypothetical pathways of their formation have been suggested. A mixture of 4 and 5 upon hydrolysis of the ring acetyl group gives the monoacetylated derivative methyl 5-(acetylamino)-1H-[1,2,4]triazole-3-carboxylate (6). The spectroscopic, structural and conformational characteristics of compounds 1-6 have been given and methods for their preparation have been provided.
Dzygiel
Anetta
A
Institute of Chemistry, University of Opole, Opole, Poland.
Rzeszotarska
Barbara
B
Masiukiewicz
Elzbieta
E
Cmoch
Piotr
P
Kamieński
Bohdan
B
D000107:Acetylation; D002851:Chromatography, High Pressure Liquid; D004952:Esters / Q000138:chemical synthesis* / Q000737:chemistry; D008401:Gas Chromatography-Mass Spectrometry; D015394:Molecular Structure; D017550:Spectroscopy, Fourier Transform Infrared; D014230:Triazoles / Q000138:chemical synthesis* / Q000737:chemistry
D004952:Esters; D014230:Triazoles; C489867:methyl 5-amino-1H-(1,2,4)triazole-3-carboxylate