Exploring Oxidant-Free Au(I)-Catalyzed C-Heteroatom Cross-CouplingReactions under CO Atmosphere

Abstract

Gold has been always considered a noble metal and traditionally, because of that, it had never been used in catalysis until about two decades ago, when first evidences of catalytic activity of some Au(I) complexes were reported. Since then, gold emerged as a late transition metal capable to catalyze reactions. Throughout the years, Au-based catalysis has experienced a fast growth and nowadays it is a promising field under deep investigation. Taking inspiration from recently reported oxidant-free Au(I)-catalyzed C-O bond forming crosscoupling reactions and well-known Pd-catalyzed carbonylative cross-coupling reactions, this work wants to be a first approach to undergo oxidant-free gold-catalyzed carbonylative crosscoupling reactions. These reactions were performed using a well studied model aryl halide macrocyclic substrate synthesized in our research group, a variety of O-nucleophiles and catalytic amounts of a Au(I) complex under CO atmosphere. The desired products were not obtained but, in contrast, the corresponding Ar-Nu coupling products were. From a synthetic point of view, it should be pointed out the importance of having synthesized a phenol as a coupling product between the aryl halide substrate and hydroxide in water. Moreover, in order to test the viability of performing carbonylative cross-coupling reactions using N-nucleophiles in a near future, we wanted to explore first the ability of gold to catalyze C-N bond forming cross-coupling reactions within the same model aryl halide substrate making use of N-nucleophiles. Here we report two N-nucleophiles (cyclohexylamine and p-nitroaniline) that did not afford the desired products and a third one (2-pyridone) that did. The corresponding coupling product had already been reported but it was synthesized via Cu(I)/Cu(III) catalysis so, to the best of our knowledge, this is the first time that this product is obtained via Au(I)/Au(III) catalysis within the macrocyclic platform. The synthesis of the substrates and the catalyst was also carried out. These compounds, together with the products of the catalyzed reactions, were all characterized by 1H-NMR and ESI-MS or ESI-HRMS