Highly efficient chiral polydentate sulfinyl ligands/catalysts containing prolinol moiety

Imidazolium-based ionic liquid functionalized chiral metal-organic framework as an efficient catalyst for asymmetric catalytic sulfoxidation

Ionic liquid (IL) units in heterogeneous catalysts exhibit synergistic effects to enhance catalytic performance and stabilize catalytically active centers, while also preventing the degradation of catalysts during the reaction process. Ionic liquid units in IL-functionalized CMOF catalysts enhance their catalytic performance in a synergistic manner. However, not only are the yields of IL-functionalized CMOFs obtained with post-synthesis methods low, but they also lead to blocking of the MOF pores and leaching of the ionic liquid. Hence, we designed and synthesized IL-functionalized chiral Ti(salen)-derivatized dicarboxylic acid as a linker coordinated with zinc nitrate to form ionic liquid functionalized CMOF (IL-Ti(salen) CMOF-n) (n = 1 and 2) catalysts. The synthesised IL-Ti(salen) CMOF-n catalyst was characterized by FT-IR, PXRD, SEM, TEM, TGA and N2 adsorption-desorption, and the catalytic performance of the IL-Ti(salen) CMOF-n was assessed using the asymmetric oxidation of methyl phenyl sulfide as a model reaction and H2O2 as an oxidant. (R)-Methyl phenyl sulfoxide with remarkable chemoselectivity (93%) and enantioselectivity (>99%) was obtained under the optimal reaction conditions. Furthermore, the catalysts demonstrated excellent recyclability after seven consecutive reuses without obvious loss of activity. This work highlights the significance of developing a new type of ionic liquid functionalized chiral heterogeneous catalyst with remarkable catalytic performance, and provides valuable guidance for the design and preparation of novel catalysts for asymmetric catalysis.

Recent advances and prospects in the Zn-catalysed Mannich reaction

Zn-catalysed reactions are ubiquitously important due to their inexpensive, generally less toxic and atom-economic nature. According to the modern criteria of sustainability, their use in a catalytic manner is a highly desirable goal, especially when using chiral ligands. Considering the relevance of well-established zinc-mediated C-C bond formation reactions, it is relatively surprising that the use of Zn as a catalyst is still underdeveloped, especially in comparison with other transition metals. The vast majority of natural molecules, including proteins, nucleic acids and most biologically active compounds, contain nitrogen. Consequently, developing new synthetic methods for the construction of nitrogenous molecules receives great attention from organic chemists. The Mannich reaction is a very basic and very useful platform for the development of several such nitrogen-containing molecules. In this review, we summarise the recent advancements in the Zn-catalysed Mannich reaction, covering the literature from 2011 to 2020.

Chiral Organosulfur Ligands/Catalysts with a Stereogenic Sulfur Atom: Applications in Asymmetric Synthesis

Asymmetric synthesis, in which chiral organocatalysts or metal complexes with chiral ligands are used, has become the most valuable methodology for the preparation of enantiomerically pure organic compounds. Among such catalysts/ligands, a growing number constitute various organosulfur compounds. This Review provides comprehensive and critical information on the plethora of sulfur-based chiral ligands and organocatalysts used in asymmetric synthesis, which have been published within the last 15 years. However, it is confined to the presentation of only those chiral catalysts/ligands that possess a stereogenic sulfur atom and includes sulfoxides, sulfinamides, N-sulfinyl ureas, sulfoximines, and some related S-chiral derivatives.