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 γ-substituted γ-butyrolactones through the arylation-lactonization reaction of the corresponding γ-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.