Nucleophilic activation of a nitrile group: Synthesis of trifluoromethyl substituted 4H-1,3,5-dioxazines

The negatively charged carbon atom of phosphorus ylides is capable of increasing the nucleophilicity of the triple CN bond. The nitrile group activated in this way can add two equivalents of hexafluoroacetone with the formation of trifluoromethyl substituted 4H-1,2,3-dioxazines. Due to delocalization of the ylidic negative charge one of the C–C bonds acquires a double bond character, the consequence of which is the existence of E/Z-isomerism in these compounds.