Gold-Catalyzed Heterocyclic Compounds Synthesis – Synt-Het-Au

The scientific approach used in this project was based on our extensive experience in the field of gold chemistry combined with our expertise in the heterogeneous and homogeneous catalysis. With these skills, we found unpublished reactivity by systematic evaluation of simple molecules with hetero atoms and carbon-carbon double bonds. The carbophilic versus oxo/azaphilic characters of gold catalysts (known as «multifaceted catalyst«) thus highlighted, allowed us to surpass their high cost. In parallel, heterogeneous and recyclable catalysts based on gold(I) associated to polyoxometalate recovery media were synthesized (hybrid organic-inorganic), characterized and tested to determine their catalytic properties, particularly compared to the literature. Their durability and resistance were evaluated by recycling cycles and post-reaction characterizations.

The duality of gold catalysts (I) has exhibited new chemical pathways to novel heterocyclic molecules of biological interest. Moreover, the design of new, stable and active gold(III) complexes, which was not originally planned, gave an additional lever of action to modulate this duality. The innovative synthesis of hybrid complexes ligand-gold(I)-polyoxometalate and their applications in heterogeneous catalysis have opened a clear gap to the design of new multifunctional molecular machines on polyoxometalates support.

Conceptually demonstrated, this duality of gold catalysts opens multiple possibilities in the development of new methods of synthesis.
The efforts focused on the design and synthesis of novel gold complexes NHC (III) to modulate the ambivalence of gold catalysts furnished the foundation for future applications, including in asymmetric gold catalysis.
Mastering a simple and effective pathway to synthetized and characterized new organic-inorganic non-covalent hybrids based on gold-polyoxometalate complexes and their applications in heterogeneous catalysis opens very interesting perspectives for both the design of others hybrids and the preparation of multifunctional molecular machinery.

Ten articles in very good peer-reviewed scientific journals have attested the excellent results obtained. Already under investigation at the beginning of the project, the multifaceted catalysis was the first provider of publications (6). Our unique strategy for non-covalent gold-based and hybrid polyoxometalates has led to 1 publication and 1 under submission. Moreover, 2 publications on the synthesis of new gold complexes (III) have been added to the assembly.

In the past decade, gold catalysts have become the reagents of choice for a variety of reactions, such as hydrogenation, C-H insertion, and nucleophilic additions, leading to a real “gold rush”. In this context, we became first interested in the possibility to find new heterocyclization reactions, highly regioselective, using catalytic amount of gold salts or complexes. Indeed, developing new cyclization methodologies is a crucial point for easily accessing to heterocyclic compounds like tetrahydrofurans or lactones. Such motifs are widespread among natural product exhibiting various biological activities (ionophore antibiotics, antiparasitic, etc...). We will then apply these novel ring forming reactions to the synthesis of such compounds. Gold catalysis is increasingly gaining interest in organic chemistry due to the efficiency, the mildness and the peculiar properties associated with gold atoms. Among these properties, alkynophilicity of gold salts or complexes already led to numerous applications, usually based on nucleophilic addition to intermediate alkyne-gold complex. In contrast, oxophilicity of gold species was far less investigated and only few examples were reported in the literature mainly based on Lewis acid activation of carbonyl compounds. In the first instance, we thus wondered if such properties, i.e. Lewis acid and alkynophilicity, could be combined, leading to new chemistry promoted by gold salts or complexes. In order to achieve this goal, we need to develop new tools, i.e. more efficient and selective catalysts, and to study mechanistically such type of domino process. Moreover, as their applications in asymmetric reactions and in natural products are still underdeveloped, gold catalyzed reactions should have the highest potential for future contributions in these fields. In the second instance, we expect to apply these new methodologies to heterogeneous catalysis using an new type of catalysts easy to handle and if possible recyclable, which can replace environmentally unfriendly reagents, and at the same time, carry out the desired organic reactions with higher yield and better selectivity. This aspect is actually a main challenge in sustainable organic chemistry.