A catalyst don’t appear in the overall stoichiometry of the reaction it catalyzes, but it must appear in at least one of the elementary reactions in the mechanism for the catalyzed reaction. 96-47-9, Name is 2-Methyltetrahydrofuran, molecular formula is C5H10O. In an article, author is Wei, Liang,once mentioned of 96-47-9, Category: chiral-nitrogen-ligands.
Catalytic Asymmetric Reactions with N-Metallated Azomethine Ylides
Optically active nitrogen-containing compounds have attracted substantial attention due to their ubiquity in the cores of natural products and bioactive molecules. Among the various synthetic approaches to nitrogenous frameworks, catalytic asymmetric 1,3-dipolar cycloadditions are one of the most attractive methods because of their powerful ability to rapidly construct various chiral N-heterocydes. In particular, N-metallated azomethine ylides, common and readily available 1,3-dipoles, have been extensively applied in dipolar cydoaddition reactions. Despite the fact that asymmetric transformations of azomethine ylides have been investigated for decades, most of the efforts have been directed toward the preparation of pyrrolidines using glycinate-derived alpha-unsubstituted aldimine esters as the precursors of the azomethine ylides. While alpha-substituted azomethine ylides derived from amino esters other than glycinate have seldom been harnessed, the construction of non-five-membered chiral N-heterocycles via 1,3-dipolar cycloadditions remains underexplored. In addition, the asymmetric alpha-functionalization of aldimine esters to prepare acyclic nitrogenous compounds such as alpha-amino acids, in which an in situ-generated N-metallated azomethine ylide serves as the nucleophile, has not been sufficiently described. In this Account, we mainly discuss the achievements we have made in the past decade toward broadening the applications of N-metallated azomethine ylides for the preparation of nitrogen-containing compounds. We began our investigation with the design and synthesis of a new type of chiral ligand, TF-BiphamPhos, which not only coordinates with Lewis acids to activate dipolar species but also serves as an H-bond donor to increase the reactivity of dipolarophiles with significantly enhanced stereochemical control. Using the Cu(I) or Ag(I)/TF-BiphamPhos complex as the catalyst, we achieved highly stereoselective (3+2) cycloadditions of glycinate and non-glycinate-derived azomethine ylides with diverse dipolarophiles, producing a variety of enantioenriched pyrrolidines with multiple stereocenters in a single step. To further expand the synthetic utility of N-metallated azomethine ylides, we successfully developed higher order cycloadditions with fulvenes, tropone, 2-aryl cydoheptatrienes, and pyrazolidinium ylides serving as the reaction partner, and this reaction provides straightforward access to enantioenriched fused piperidines, bridged azabicyclic frameworks, and triazines via (3+6)- and (3+3)-type cycloadditions. Using N-metallated azomethine ylides as the nucleophile, we realized Cu(I)-catalyzed asymmetric 1,4-Michael additions with alpha,beta-unsaturated bisphosphates/Morita-Baylis-Hillman products, furnishing an array of structurally diverse unnatural alpha-amino acids. Based on the strategy of synergistic activation, we achieved highly efficient dual Cu/Pd and Cu/Ir catalysis for the alpha-functionalization of aldimine esters via the asymmetric allylic/allenylic allcylation of N-metallated azomethine ylides. Notably, Cu/Ir catalysis allowed the stereodivergent synthesis of alpha,alpha-disubstituted alpha-amino acids via a branched allylic alkylation reaction, in which the two distinct chiral metal catalysts independently have full stereochemical control over the corresponding nucleophile and electrophile. Furthermore, an expedient and stereodivergent preparation of biologically important tetrahydro-gamma-carbolines was realized through a Cu/Ir-catalyzed cascade allylation/iso-Pictet-Spengler cyclization. In addition, when the steric congestion in the allylation intermediates was increased, the combined Cu/Ir catalysts provided an asymmetric cascade allylation/2-aza-Cope rearrangement, producing various optically active homoallylic amines with impressive results.
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Reference:
Chiral nitrogen ligands in late transition metal-catalysed asymmetric synthesis¡ªI. Addressing the problem of ligand lability in rhodium-catalysed hydrosilations,
,Nitrogen-Containing Ligands for Asymmetric Homogeneous and Heterogeneous Catalysis