Double A³ -Coupling of Primary Amines Catalysed by Gold Complexes

A novel family of dipropargylamines has been synthesised in one pot through a double catalytic A³ -coupling of five components. Cationic [Au^I -L][SbF₆ ] complexes (L=JohnPhos) are extremely active catalysts for the double A³ -coupling of primary amines (aliphatic or aromatic), formaldehyde and trimethylsilylacetylene. Several reactions of LAu-amine complexes with organic reagents were studied and followed by NMR and HRMS (ESI) analyses, providing information about the reaction mechanism. Specifically, the role of the π-gold(I) acetylide complexes as active catalyst species was firmly confirmed. Most of the intermediates of this five-component coupling were identified by GC-MS spectrometry, lending support to the mechanistic proposal. In some cases, cationic amine-gold(I)-L complexes corresponding to the activated reagent or intermediate were isolated and characterised by single-crystal X-ray diffraction analysis, their spectroscopic properties were recorded, and their catalytic activity evaluated. Protic solvents influence the course of the reaction by effecting the double deprotection of dipropargylamines, providing a convenient route to dipropargylamines with double-deprotected silyl moieties. When NaOH is present in the reaction media, formation of cationic acetylide-dipropargylamine gold(I) and neutral hydroxide LAuOH complexes, respectively, as high and less active intermediate catalyst forms occur.