Pyridine‐Hydrazone Ligands in Asymmetric Palladium‐Catalyzed 1,4‐ and 1,6‐Additions of Arylboronic Acids to Cyclic (Di)enones

Enantioselective synthesis of α-aryl α-hydrazino phosphonates

Catalysts generated in situ by the combination of pyridine-hydrazone N,N-ligands and Pd(TFA)2 have been applied to the addition of arylboronic acids to formylphosphonate-derived hydrazones, yielding α-aryl α-hydrazino phosphonates in excellent enantioselectivities (96 → 99% ee). Subsequent removal of the benzyloxycarbonyl (Cbz) N-protecting group afforded key building blocks en route to appealing artificial peptides, herbicides and antitumoral derivatives. Experimental and computational data support a stereochemical model based on aryl-palladium intermediates in which the phosphono hydrazone coordinates in its Z-configuration, maximizing the interactions between the substrate and the pyridine-hydrazone ligand.

Enantioselective construction of ortho-substituted benzylic quaternary centers using a phenanthroline-Pd catalyst

An efficient and enantioselective construction of ortho-substituted benzylic all-carbon quaternary centers via chiral phenanthroline-Pd complex catalyzed conjugate addition has been developed.

Recent advances in palladium-catalysed asymmetric 1,4-additions of arylboronic acids to conjugated enones and chromones

The transition metal (palladium)-catalysed asymmetric 1,4-addition of arylboronic acids to conjugated enones belong to the most important and emerging strategies for the construction of C-C bonds in an asymmetric fashion. This review covers known catalytic systems used for this transformation. For clarity, we are using the type of ligand as a sorting criterion. Finally, we attempted to create a flowchart facilitating the selection of a suitable ligand for a given combination of enone and arylboronic acid.

Stereoselectivity Predictions for the Pd-Catalyzed 1,4-Conjugate Addition Using Quantum-Guided Molecular Mechanics

The conjugate addition of aryl boronic acids to enones is a powerful synthetic tool to introduce quaternary chiral centers, but the experimentally observed stereoselectivities vary widely, and the identification of suitable substrate-ligand combinations requires significant effort. We describe the development and application of a transition-state force field (TSFF) by the quantum-guided molecular mechanics (Q2MM) method that is validated using an automated screen of 9 ligands, 38 aryl boronic acids, and 22 enones, leading to a MUE of 1.8 kJ/mol and a R² value of 0.877 over 82 examples. A detailed error analysis identified the structural origin for the deviations in the small group of outliers. The TSFF was then used to predict the stereoselectivity for 27 ligands and 59 enones. The vast majority of the virtual screening results are in line with the expected results. Selected results for 6-substituted pyrox ligands, which were not part of the training set, were followed up by density functional theory and experimental studies.

Iron-Catalyzed Conjugate Addition of Aryl Iodides onto Activated Alkenes under Air in Water

The combination of commercially available FeCl3·6H2O with a water-soluble cationic 2,2′-bipyridyl catalytic system was found to enable the direct conjugate addition of aryl iodides onto activated alkenes, such as an α,β-unsaturated ester and a ketone, in a weakly acidic aqueous solution. This operationally simple protocol was carried out at 80 °C under air atmosphere in a potassium acetate-buffered aqueous solution for 12 h in the presence of Zn dust as a reductant to provide the desired 1,4-adducts in good yields.

Asymmetric Synthesis of 1-Tetralones Bearing A Remote Quaternary Stereocenter through Rh-Catalyzed C-C Activation of Cyclopentanones

Herein, we describe the preparation of 1-tetralones bearing a remote quaternary stereocenter in a highly enantioselective manner. A sequence of Pd-catalyzed asymmetric 1,4-addition and Rh-catalyzed enantiospecific C-C/C-H activation delivers diverse 1-tetralones with a C4 quaternary stereocenter, which are prepared in good overall yields and high enantioselectivity.

Natural carbolines inspired the discovery of chiral CarOx ligands for asymmetric synthesis and antifungal leads

Natural carboline-inspired novel chiral β-CarOx ligands were designed and synthesized for asymmetric synthesis and discovery of antifungal leads.

Catalytic enantioselective synthesis of α-aryl α-hydrazino esters and amides

Asymmetric 1,2-addition of aryl boronic acids to N-carbamoyl (Cbz and Fmoc) protected glyoxylate-derived hydrazones affords α-aryl α-hydrazino esters/amides, key building blocks en route to artificial peptides.

Pd(II)-Catalyzed Enantioselective Desymmetrization of Polycyclic Cyclohexenediones: Conjugate Addition versus Oxidative Heck

Pd(II)-catalyzed desymmetrization of polycyclic cyclohexenediones has been achieved with high enantio- and diastereoselectivities. Up to five contiguous stereocenters are desymmetrized, while simultaneously, an additional stereocenter is created by the enantioselective conjugate addition. Surprisingly, the conjugate addition products dominate even under typical oxidative Heck conditions, and these observations may provide some insight into the competition between the two related reactions.