Rhodium-Catalyzed Asymmetric C-H Functionalization Reactions.

This review summarizes the advancements in rhodium-catalyzed asymmetric C-H functionalization reactions during the last two decades. Parallel to the rapidly developed palladium catalysis, rhodium catalysis has attracted extensive attention because of its unique reactivity and selectivity in asymmetric C-H functionalization reactions. In recent years, Rh-catalyzed asymmetric C-H functionalization reactions have been significantly developed in many respects, including catalyst design, reaction development, mechanistic investigation, and application in the synthesis of complex functional molecules. This review presents an explicit outline of catalysts and ligands, mechanism, the scope of coupling reagents, and applications.

Electrophile-Arene Affinity: An Energy Scale for Evaluating the Thermodynamics of Electrophilic Dearomatization Reactions.

Rational design and development of organic reactions are lofty goals in synthetic chemistry. Quantitative description of the properties of molecules and reactions by physical organic parameters plays an important role in this regard. In this Article, we report an energy scale, namely, electrophile-arene affinity (EAA), for evaluating the thermodynamics of electrophilic dearomatization reactions, a class of important transformations that can rapidly build up molecular complexity and structural diversity by converting planar aromatic compounds into three-dimensional cyclic molecules. The acquisition of EAA data can be readily achieved by theoretically calculating the enthalpy changes (ΔH) of the hypothetical reactions of various (cationic) electrophiles with aromatic systems (taking the 1-methylnaphthalen-2-olate ion as an example in this study). Linear correlations are found between the calculated ΔH values and established physical organic parameters such as the percentage of buried volume %VBur (steric effect), Hammett's σ or Brown's σ+ (electronic effect), and Mayr's E (reaction kinetics). Careful analysis of the ΔH values leads to the rational design of a dearomative alkynylation reaction using alkynyl hypervalent iodonium reagents as the electrophiles.

Explicit Mechanism of Rh(I)-Catalyzed Asymmetric C-H Arylation and Facile Synthesis of Planar Chiral Ferrocenophanes.

Mechanism-guided reaction development is a well-appreciated research paradigm in chemistry since the merging of mechanistic knowledge would accelerate the discovery of new synthetic methods. Low-valent transition metals such as Pd(0)- and Rh(I)-catalyzed C-H arylation with aryl (pseudo)halides is among the enabling reactions for the exclusive cross-coupling of two different aryl partners. However, different from the situation of Pd(0)-catalysis, the mechanism of Rh(I)-catalyzed C-H arylation is underexplored. The sequence of the elementary steps of aryl C-H activation and oxidative addition of aryl (pseudo)halides remains unclear. Herein, we report comprehensive experimental and computational studies toward explicit mechanistic understandings of Rh(I)-catalyzed intermolecular asymmetric C-H arylation between 2-pyridinylferrocenes and aryl bromides. The identification of each elementary step in the catalytic cycle and the structural characterization of the key intermediates and transition states allow the rational design and development of challenging intramolecular reactions. The successful realization of this reaction mode set the foundation for the facile synthesis of planar chiral [m]ferrocenophanes (m = 6-8), a class of rarely explored target molecules with strained structures and intriguing molecular topology.

Visible-light induced dearomatization reactions.

Dearomatization reactions provide rapid access to structurally complex three-dimensional molecules from simple aromatic compounds. Plenty of reports have demonstrated their utilities in the synthesis of natural products, medicinal chemistry, and materials science in the last decades. Recently, visible-light mediated photocatalysis has emerged as a powerful tool to promote many kinds of transformations. The dearomatization reactions induced by visible-light have also made significant progress during the past several years. This review provides an overview of visible-light induced dearomatization reactions classified based on the manner in which aromaticity is disrupted.

Stereodivergent Construction of 1,3-Chiral Centers via Tandem Asymmetric Conjugate Addition and Allylic Substitution Reaction.

Herein, we report a synthesis of cyclohexanones bearing multi-continuous stereocenters by combining copper-catalyzed asymmetric conjugate addition of dialkylzinc reagents to cyclic enones with iridium-catalyzed asymmetric allylic substitution reaction. Good to excellent yields, diastereoselectivity and enantioselectivity can be obtained. Unlike the stereodivergent construction of adjacent stereocenters (1,2-position) reported in the literature, the current reaction can achieve the stereodivergent construction of nonadjacent stereocenters (1,3-position) by a proper combination of two chiral catalysts with different enantiomers.