ChemInform Abstract: SYNTHESIS OF 2,5‐SUBSTITUTED 1,3,4‐OXADIAZOLES

Abstract

Die Umsetzung der Carbonsäuren (I) mit Hydrazinhydrochlorid (II) in Phosphoroxychlorid bei Temperaturen von 85 ‐ 120°C evtl. in Gegenwart von Phosphorpentachlorid führt zu den Oxadiazolen (III).

2,5-Bis(trifluoromethyl)-1,3,4-oxadiazole

“…3 The syntheses of other 2,5-bis(perfluoroalkyl)-1,3,4-oxadiazoles by the intramolecular dehydration of N,N 1 -diacylhydrazines have been reported, 4,5 including a case in which PCl 5 was used to effect cyclization. 6 A different approach involves controlled heating (95 • C, 30 min + 105 • C, 30 min + 200 • C, 30 min) of 5-(trifluoromethyl)-3H-1,2,3,4-tetrazole (3) with trifluoroacetyl chloride thereby forming the N-acyl derivative 4 which ejects dinitrogen to form a putative 1,3-dipolar species. 7 Intramolecular electrophilic attack at oxygen in the 1,3-dipole produces 2 in 95% yield (eq 1, part b).…”

“…The synthesis of 3,6-bis(trifluoromethyl)-s-tetrazine (7) was achieved in a two-step procedure from 2 involving formation of dihydrotetrazine (6), by treatment with hydrazine in ethanol, followed by oxidation with FeCl 3 (eq 1, part c). 4 Subsequently, the reaction was re-investigated using 19 F NMR analysis of reaction mixtures and products.…”