strategy for the synthesis of 1,3,4-oxadiazoles was established through direct annulation of hydrazides with methylketones. It was found that the use of K2CO3 as a base achieves an unexpected and highly efficient C–C bondcleavage. This reaction is proposed to go through oxidativecleavage of Csp3–H bonds, followed by cyclization and deacylation.
通过将酰肼与甲基酮直接环合,建立了一种合成1,3,4-恶二唑的新策略。发现使用K 2 CO 3作为碱可以实现意想不到且高效的C–C键裂解。建议该反应通过C sp 3 -H键的氧化裂解,然后环化和脱酰基。
DMF as Methine Source: Copper‐Catalyzed Direct Annulation of Hydrazides to 1,3,4‐Oxadiazoles
作者:Shoucai Wang、Kai Wang、Xiangfei Kong、Shuhua Zhang、Guangbin Jiang、Fanghua Ji
DOI:10.1002/adsc.201900395
日期:2019.9.3
unprecedented Cu‐catalyzeddirectannulation of hydrazides with N,N‐dimethylformamide (DMF) was developed, providing an efficient synthesis of valuable 1,3,4‐oxadiazoles. This process features the short reaction time and can be safely conducted on gram scale. The reaction also facilitated the convenient synthesis of 1,3,4‐oxadiazole‐2(3H)‐ones. Moreover, the mechanistic studies suggest that the source of CH is
[4 + 1] Cyclization of benzohydrazide and ClCF2COONa towards 1,3,4-oxadiazoles and 1,3,4-oxadiazoles-d5
作者:Ya Wang、Shiqiang Mu、Xin Li、Qiuling Song
DOI:10.1016/j.cclet.2021.08.089
日期:2022.3
A facilesynthesis of 1,3,4-oxadiazoles and 1,3,4-oxadiazoles-d5 via [4 + 1] cyclization of ClCF2COONa with non-amine compounds containing amino groups is developed. Of note, this is the first time that halofluorinated compounds are used as C1 synthon to construct deuterated nitrogen-heterocyclic compounds. The current protocol features simple operation, readily accessible raw materials, wide substrate
Three series of substituted1,3,4-oxadiazoles were studied by (17)O NMR spectroscopy. Chemical shifts values were correlated with empirical Hammett parameters as well as calculated bond lengths and chemical shielding values.
15N NMR chemicalshifts of 2‐aryl‐1,3,4‐oxadiazoles were assigned on the basis of the 1H–15N HMBC experiment. Chemicalshifts of the nitrogen and carbon atoms in the oxadiazole ring correlate with the Hammett σ‐constants of substituents in the aryl ring (r2 ≥ 0.966 for N atoms). 15N NMR data are a suitable and sensitive means for characterizing long‐range electronic substituenteffects. Additionally