The design and development of site-isolating and multifunctional catalysts for multistep sequential reactions at the molecular level is a significant challenge. Herein, we first report bifunctional metal NPs?chiral MOFs catalysts for asymmetric sequential reactions. Pd nanoparticles and chiral proline were successfully added to NH2-UiO-66 to construct two chiral bifunctional catalysts, in which active Pd nanoparticles were encapsulated into the frameworks via the "bottle-around-ship" method, and chiral proline was introduced into NH2-UiO-66 by coordination to zirconium nodes and postsynthetic modification (PSM) of the organic linkers. The chiral proline-decorated bifunctional Pd?NH2-UiO-66 catalysts were applied to sequential Suzuki coupling/asymmetric aldol reactions with excellent coupling performance (yields up to 99.9%) and good enantioselectivities (eeanti values up to 97%). The heterogeneous catalyst by coordination of proline can be reused, and the reaction activity was not significantly reduced after four cycles.
Sequential Suzuki/asymmetric aldol and Suzuki/Knoevenagel reactions under aqueous conditions
Here we describe for the first time a sequential Suzuki/asymmetric aldol reaction. Such sequential approach was achieved through the combined use of an ionic liquid supported palladium catalyst and the organocatalyst trans-4-(2,2-diphenylacetoxy)proline. Suzuki and asymmetric aldol reactions were performed under aqueous conditions. The use of a palladium catalyst under basic conditions allowed also the first example of sequential Suzuki/Knoevenagel reaction. Reactions were carried out under aqueous conditions and products were isolated in good to high yields and, in the case of the Suzuki/aldol reaction, with diastereoselectivities up to 91:9 and enantioselectivities up to at least 99%.