Hemilabile MIC∧N ligands allow oxidant-free Au(i)/Au(iii) arylation-lactonization of γ-alkenoic acids

Oxidant-free Au-catalyzed reactions are emerging as a new synthetic tool for innovative organic transformations. Oxidant-free Au-catalyzed reactions are emerging as a new synthetic tool for innovative organic transformations. Still, a deeper mechanistic understanding is needed for a rational design of these processes. Here we describe the synthesis of two Au(i) complexes bearing bidentated hemilabile MIC<^>N ligands, [Au-I(MIC<^>N)Cl], and their ability to stabilize square-planar Au(iii) species (MIC = mesoionic carbene). The presence of the hemilabile N-ligand contributed to stabilize the ensuing Au(iii) species acting as a five-membered ring chelate upon its coordination to the metal center. The Au(iii) complexes can be obtained either by using external oxidants or, alternatively, by means of feasible oxidative addition with strained biphenylene C-sp(2)-C-sp(2) bonds as well as with aryl iodides. Based on the fundamental knowledge gained on the redox properties on these Au(i)/Au(iii) systems, we successfully develop a novel Au(i)-catalytic procedure for the synthesis of gamma-substituted gamma-butyrolactones through the arylation-lactonization reaction of the corresponding gamma-alkenoic acid. The oxidative addition of the aryl iodide, which in turn is allowed by the hemilabile nature of the MIC<^>N ligand, is an essential step for this transformation.

Automated summary

Oxidant-free Au-catalyzed reactions are gaining attention as a new tool for innovative organic transformations. This study successfully demonstrated the synthesis of two Au(i) complexes and proposed a rational design for oxidant-free Au-catalyzed reactions. A novel Au(i)-catalytic procedure for the synthesis of gamma-substituted gamma-butyrolactones was developed based on the fundamental knowledge gained on the redox properties of Au(i)/Au(iii) systems.