Reagent/Substituent Switching Approach for the Synthesis of Substituted 1,3,4‐Oxadiazole/1,3,4‐Oxadiazoline and 1,2,4‐Triazole Derivatives from N‐Substituted Hydrazides

Abstract

A metal‐free method for the synthesis of substituted 1,3,4‐oxadiazole/1,3,4‐oxadiazoline and 1,2,4‐triazole derivatives from a common starting material via reagent/substituent switching is reported. In the presence of 2‐fluoropyridine/triflic anhydride, 1,3,4‐oxadiazole derivatives were exclusively formed from N′‐tert‐butylhydrazides and 1,3,4‐oxadiazoline derivatives were produced from N‐phenylhydrazides. On the other hand, when using pyridine/triflic anhydride, salts of 1,2,4‐triazoles were the sole products.magnified image

Cobalt(II) nitrate promoted cyclization of benzoyl hydrazone for the synthesis of 2,5-diphenyl-1,3,4-oxadiazole derivatives

“…Unless otherwise noted. All compounds were characterized by 1 H NMR and 13 C NMR, which are consistent with those reported in the literature.…”

“…(Table 1, entry 11). When the temperature was reduced to 80 °C and 100 °C or increased to 120 °C, the yield decreased to 57%, 78%, and 84%, respectively (Table 1, entries [12][13][14]. Considering the influence of cobalt salts, we found that Co(NO 3 ) 2 •6H 2 O is the only effective one (Table 1, entries 1, 15 −17).…”

“…4,5 In view of their great importance, the synthesis of 2,5-diaryl-1,3,4-oxadiazoles has gained much attention in recent decades and many useful synthetic procedures for their preparation have been developed. For example, arylation of 1,3,4-oxadiazoles (Scheme 1(a)), [6][7][8] aminocarbonylation reaction of aryl halides with chloroform and tetrazoles (Scheme 1(b)), [9][10][11][12] oxidative dehydrogenation of N-substituted hydrazides (Scheme 1(c)), 13 oxidations of aldehyde hydrazones and N, N-dimethylamides (Scheme 1(d)), 14 isocyanide insertion/cyclization sequence of hydrazides and aryl halide (Scheme 1(e)), 15 the use of Vilsmeier's reagent (Scheme 1(f)), 16,17 decarboxylation and cyclization of α-keto acids with acylhydrazines (Scheme 1(g)), 18,19 oxidative cyclization using aldehydes and acyl hydrazides (Scheme 1(h)). [20][21][22][23][24][25][26][27][28][29][30][31] As shown in Scheme 2, many different methods have been developed for the synthesis of 2,5-substituted-1,3,4-oxadiazoles from aldehydes and acyl hydrazides (Scheme 1(h)).…”

Facile Synthesis of Tricyclic 1,2,4-Oxadiazolines-Fused Tetrahydro-Isoquinolines from Oxime Chlorides with 3,4-Dihydroisoquinoline Imines

“…However, the imines compounds, especially for alkyl imines, are rather labile substrates for their preparation [ 15 ]. Another approach to the construction of 1,2,4-oxadiazole skeletons is produced by the condensation of amidoximes with a carbonyl compound [ 18 , 19 , 20 , 21 ]. These condensation reactions existed under often harsh reaction conditions.…”