Flash vacuum pyrolysis of 1,2,5-oxadiazole 2-oxides and 1,2,3-triazole 1-oxides

Abstract

The flash vacuum pyrolysis (FVP, 450-600 ºC/10 -3 mmHg) of 3,4-diaryl-and 3,4-dialkyl-1,2,5-oxadiazole 2-oxides (furoxans) has been investigated. In all cases the 1,2,5-oxadiazole ring cleaved cleanly at O(1)-N(2) and C(3)-C(4) to afford two nitrile oxide fragments, which were trapped in high yield (75-97%) as their isoxazoline cycloadducts by reaction with alk-1-enes. At higher temperatures (700-800 ºC) isocyanates were formed as by-products. The dimerisation of acetonitrile oxide to dimethylfuroxan was followed by 1 H NMR spectroscopy, and the rate constant for the 2 nd order reaction determined. The furoxans were converted into isocyanates in good yield (61-95%) by FVP, followed by sulfur dioxide-mediated isomerisation of the resulting nitrile oxides. 2,4,5-Trisubstituted-1,2,3-triazole 1-oxides showed greater thermal stability, but at 700-800 ºC decomposition of the 4,5-dimethyl compound 25b lead to 1,2-di(5-methyl-2-phenyl-1,2,3-triazol-2-yl)ethane as the major product; attempts to trap acetonitrile oxide were unsuccessful.

Preparation of Viscosity-Sensitive Isoxazoline/Isoxazolyl-Based Molecular Rotors and Directly Linked BODIPY–Fulleroisoxazoline from the Stable meso-(Nitrile Oxide)-Substituted BODIPY

“…Because of their rapid dimerization to 1,2,5-oxadiazole 2-oxides (furoxans), they are usually prepared in situ, which often limits their use in organic synthesis. The spontaneous dimerization to furoxans can be prevented by steric shielding of the nitrile oxide fragment facilitated by the nearby substituents, in particular, by methyl groups …”

From Humorous Post to Detailed Quantum-Chemical Study: Isocyanate Synthesis Revisited

“…This assumption also bridges the suggested mechanism with a reaction between nitrile oxides and sulfinylamines that results in carbodiimides. [22,23] However, such a chemical transformation caused some confusion when one of our research team members came across a post on the VK social network. [15] Thus, an idea to create a crowd-effort project to study this rearrangement pathway came out.…”

From a humorous post to a detailed quantum-chemical study: isocyanate synthesis revisited

“…This assumption also bridges the suggested mechanism with a reaction between nitrile oxides and sulfinylamines that results in carbodiimides. 21,22 However, such a chemical transformation caused some confusion when one of our research team members came across a post on the VK social network. 23 Thus, an idea to create a crowd-effort project to study this rearrangement pathway came out.…”