Natural Deep Eutectic Solvents as an Efficient and Reusable Catalytic System for the Nazarov Cyclization

Natural Deep Eutectic Solvents have emerged as alternative non-toxic, non-aqueous solvents for an increasing number of synthetic transformations. Remarkably, in some cases one or more of the NaDES components plays an active role in the reaction mechanism and directly participates as either a catalyst or a reagent in the reaction. In this paper, we formulated several NaDES in which one of the components is a carboxylic acid and used them as medium to perform Nazarov cyclizations on divinyl ketones to obtain cyclopentenones, a widespread motif in natural compounds. The reaction conditions were optimized and the scope investigated on C-, O- and N-derived compounds. To assess the full sustainability of the proposed approach, the recyclability and scalability of the process were investigated, thus proving that multi-grams preparations are possible with complete recycle of the medium.