RESUMEN
Azomethine imines can be accessed upon heating appropriate alkynylhydrazide precursors. This simple thermal hydroamination approach allows the formation of five- and six-membered dipoles in modest to excellent yields. The structure of the acyl group is important to minimize side reactions and allow the isolation of the azomethine imines by column chromatography.
Asunto(s)
Alquinos/química , Compuestos Azo/síntesis química , Hidralazina/química , Iminas/síntesis química , Tiosemicarbazonas/síntesis química , Compuestos Azo/química , Iminas/química , Estructura Molecular , Tiosemicarbazonas/químicaRESUMEN
Benzoic hydrazides (R = Ph), which are remarkably bench and thermally stable reagents (often up to 230 degrees C), afford intramolecular hydroamination products upon heating at high temperatures (120-235 degrees C). A concerted Cope-type hydroamination event, followed by a hydrazide-mediated proton transfer step of the hydrazinium ylide intermediate, is proposed and supported by DFT calculations. In contrast, a simple modification of the reagent structure (R = Ot-Bu or NH(2)) favors the formation of aminocarbonylation products at 200 degrees C, and the latter reaction is shown to be stereospecific.