4,5‐Dihydro‐1,2,3‐oxadiazole: A Very Elusive Key Intermediate in Various Important Chemical Transformations

Abstract

4,5-Dihydro-1,2,3-oxadiazoles are postulated to be key intermediates in the industrial synthesis of ketones from alkenes, in the alkylation of DNA in vivo, and in the decomposition of N-nitrosoureas; they are also a subject of great interest for theoretical chemists. In the presented report, the formation of 4,5-dihydro-1,2,3-oxadiazole and the subsequent decay into secondary products have been studied by NMR monitoring analysis. The elusive properties evading characterization have now been confirmed by (1) H, (13) C, and (15) N NMR spectroscopy, and relevant 2D experiments at very low temperatures. Our experiments with suitably substituted N-nitrosoureas using thallium(I) alkoxides as bases under apolar conditions answer important questions on the existence and the secondary products of 4,5-dihydro-1,2,3-oxadiazole.

Experimental observation and quantum chemical investigation of thallium(i) (Z)-methanediazotate: synthesis of a long sought and highly reactive species

“…Therefore, 15 N-labelled N-methyl-N-nitrosourea (7) was synthesised and reacted with TlOEt at À40 C in CD 2 Cl 2 , under constant monitoring by low-temperature NMR spectroscopy. 10 In this case, we could only observe the doublet for CH 2 N 15 11 This result is in complete agreement with the known methods for the synthesis of diazotates and the observed secondary products in the absence of electrophiles (Scheme 2). 11 However, owing to our previous experience with thallium(I) alkoxides, it is known that TlOEt and thallium(I) propoxide (TlOPr) 9a react differently, probably because of their varying association nature.…”

The Effect of 1,2- and trans-1,4-Units on Ketonization of Polybutadienes by Nitrous Oxide

“…The results on the oxygenation of trans -PB rubber by N 2 O can be described by a mechanism similar to that for ketonization of internal and terminal olefins , and polydienes like cis -1,4-butadiene rubber. , The reaction most likely proceeds through the 1,3-dipolar cycloaddition of N 2 O to the double bond involving the formation of the unstable 4,5-dihydro-[1,2,3]-oxadiazole intermediate, which decomposes to yield a carbonyl product. ,,− …”

Liquid-Phase Oxidation of Butene–Butane Mixtures with N2O to Ketones and Aldehydes

“…Since 1990s, nitrous oxide (N 2 O) has also attracted growing interest not only as a climate-relevant greenhouse gas generated as a waste product in some chemical processes − but also as an efficient oxygen donor due to its promise for selective oxidation. ,− In particular, the non-catalytic oxidation of olefins with N 2 O via the 1,3-dipolar cycloaddition mechanism − (e.g., Scheme ) opens a route for the direct synthesis of valuable carbonyl compounds (ketones and aldehydes). ,,,− …”