Cobalt-Catalyzed Chemo- and Stereoselective Transfer Semihydrogenation of 1,3-Dienes with Water as a Hydrogen Source

(Z)-1,2-Disubstituted, trisubstituted, and tetrasubstituted alkenes are not only important units in medicinal chemistry, natural product synthesis, and material science but also useful intermediates in organic synthesis. Development of catalytic stereoselective transformations to access multisubstituted alkenes with various substitution patterns from easily accessible modular starting materials and readily available catalysts is a crucial goal in the field of catalysis. Water is an ideal hydrogen source for catalytic transfer hydrogenation despite of the high difficulty to activate water. Here, we report a cobalt-catalyzed protocol for regio- and stereoselective transfer semihydrogenation of 1,3-dienes to construct a broad scope of (Z)-1,2-disubstituted, (Z)-, (E)-trisubstituted, and tetrasubstituted alkenes in high stereoselectivity with H2O as the hydrogen source. Mechanistic studies revealed that the reactions proceeded through a unique Co(I)/Co(III) cycle and involved a 1,4-cobalt shift process, which is an unprecedented reaction pathway, providing a new platform for modular synthesis of multisubstituted alkenes as well as opportunities for designing novel reaction modes and pushing forward the advancement in organocobalt chemistry.

Palladium-Catalyzed Regiodivergent Three-Component Alkenylamination of 1,3-Dienes with Alkyl and Aryl Amines

We report a palladium-catalyzed method for 4,3- or 4,1-selective alkenylamination of terminal dienes. Three-component couplings proceed with alkenyl triflates and several amines, giving vicinal carboamination with a Xantphos-supported catalyst and distal difunctionalization with a phosphoramidite ligand. A number of constitutionally different disubstituted dienes also participate in regiodivergent carboaminations. Experimental evidence indicates that selectivity in the Xantphos reactions is largely influenced by the substrate, whereas the phosphoramidite-promoted process is catalyst controlled, orchestrated by a key π-stacking interaction among the ligand, solvent, and substrate.

Switch in Selectivities by Dinuclear Nickel Catalysis: 1,4-Hydroarylation of 1,3-Dienes to Z-Olefins

One of the most challenging tasks in organic synthesis is to control selectivities, especially switching the well-known selectivity to obtain new isomers that were previously inaccessible. Inspired by biological catalysis involving multiple metal centers, catalysis enabled by binuclear metal complexes offers the potential to induce reactivity and selectivity that might not be available to mononuclear catalysts. Herein, we describe that using a macrocyclic bis pyridyl diimine dinickel complex as the catalyst, the commonly observed 4,3-regioselectivity of hydroarylation of 1,3-dienes is switched to 1,4-hydroarylation with thermodynamically less stable Z-stereoselectivity, offering challenging synthetic target Z-olefins. DFT calculations show that the activation of 1,3-diene proceeds through dinuclear Ni-diolefin coordination, and the synergistic effects of two Ni nuclei enable reactivity and selectivity of this binuclear catalysis substantially different from those of mononuclear nickel complexes in the current reaction.

Nickel/Brønsted acid dual-catalyzed regioselective C–H bond allylation of phenols with 1,3-dienes

A nickel/Brønsted acid dual-catalyzed C-H bond ortho-allylation of phenols with 1,3-dienes has been developed. This methodology is readily applicable to the modification of complex pharmaceutical molecules.

Orthogonal Regulation of Nucleophilic and Electrophilic Sites in Pd-Catalyzed Regiodivergent Couplings between Indazoles and Isoprene

Depending on the reactant property and reaction mechanism, one major regioisomer can be favored in a reaction that involves multiple active sites. Herein, an orthogonal regulation of nucleophilic and electrophilic sites in the regiodivergent hydroamination of isoprene with indazoles is demonstrated. Under Pd-hydride catalysis, the 1,2- or 4,3-insertion pathway with respect to the electrophilic sites on isoprene could be controlled by the choice of ligands. In terms of the nucleophilic sites on indazoles, the reaction occurs at either the N¹ - or N² -position of indazoles is governed by the acid co-catalysts. Preliminary experimental studies have been performed to rationalize the mechanism and regioselectivity. This study not only contributes a practical tool for selective functionalization of isoprene, but also provides a guide to manipulate the regioselectivity for the N-functionalization of indazoles.

External electric field: a new catalytic strategy for the anti-Markovnikov hydrohydrazination of parent hydrazine

The anti-Markovnikov hydroamination reaction is considered to be a particular challenge, and one of the reactants, parent hydrazine, is also regarded as a troubling reagent. In this study, we first studied the hydrohydrazination of parent hydrazine via an effective and green catalyst—external electric field (EEF). The calculation results demonstrated that the anti-Markovnikov and Markovnikov pathways are competitive when there was no catalyst. EEF oriented along the negative direction of the X axis (F_x) accelerated the anti-Markovnikov addition reaction. Moreover, it lowered the barrier height of the first step by 16.0 kcal mol⁻¹ (from 27.8 to 11.8 kcal mol⁻¹) when the field strength was 180 (×10⁻⁴) au. Under the same conditions, the Markovnikov reaction pathway was inhibited, which means that EEF achieved the specificity of hydrohydrazination. The solvents are favorable for the first step addition reaction, particularly the synergy between solvents and F_x lowered the barrier heights by 8.3 (C₆H₆) and 10.7 (DMSO) kcal mol⁻¹ for an F_x = −60 (×10⁻⁴) au. Besides, the introduction of the electron-withdrawing substituent (trifluoromethyl) is also a good strategy to catalyze hydrohydrazination, while the electron-donating group (methoxy) is unfavorable.

The anti-Markovnikov hydrohydrazination of parent hydrazine were catalyzed by external electric field (EEF) to a large extent. Furthermore, the solvent effects and the substituent effects of the hydrohydrazination were enhanced in the presence of EEF.

Photocatalytic Generation of Aminium Radical Cations for C─N Bond Formation

Aminium radical cations have been extensively studied as electrophilic aminating species that readily participate in C─N bond forming processes with alkenes and arenes. However, their utility in synthesis has been limited, as their generation required unstable, reactive starting materials and harsh reaction conditions. Visible-light photoredox catalysis has emerged as a platform for the mild production of aminium radical cations from either unfunctionalized or N-functionalized amines. This Perspective covers recent synthetic methods that rely on the photocatalytic generation of aminium radical cations for C─N bond formation, specifically in the context of alkene hydroamination, arene C─H bond amination, and the mesolytic bond cleavage of alkoxyamines.

Catalysis and regioselectivity in hydrofunctionalization reactions of unsaturated carbon bonds. Part II. Hydroamination

This review continues consideration of the regioselectivity problem in the catalyzed hydrofunctionalization of unsaturated organic compounds and addresses hydroamination of unsaturated hydrocarbons. Particular parts of the review deal with reactions of alkenes, alkynes, allenes and dienes. It is shown that the selectivity of hydroamination depends on the natures of the reactants and the catalyst. Conditions of the reactions are described; in some cases, reaction mechanisms are discussed. Reactions for which divergent regioselectivity is possible are noted.

The bibliography includes 249 references.

Dedicated to the memory of V.V.Markovnikov.

Pd-Catalyzed Stereodivergent Allylic Amination of α-Tertiary Allylic Alcohols towards α,β-Unsaturated γ-Amino Acids

Tertiary allylic alcohols were conveniently converted into either (Z)- or (E)-configured α,β-unsaturated γ-amino acids by treatment with secondary amines under Pd catalysis at ambient conditions. The key to control the stereochemical course of these formal allylic aminations was the presence of a suitable diphosphine ligand, with dppp [1,3-bis(diphenylphosphino)propane, L12] providing high yields and selectivities for the (Z) isomers, whereas the bis[(2-diphenylphosphino)phenyl]ether (DPEPhos) derivative L1' allowed for selective formation of the corresponding (E) isomeric products. This ligand-controlled, stereodivergent protocol thus shows promise for the stereoselective preparation of allylic amine products from a common substrate precursor.

Mechanistically Guided Design of Ligands That Significantly Improve the Efficiency of CuH-Catalyzed Hydroamination Reactions

Using a mechanically guided ligand design approach, a new ligand (SEGFAST) for the CuH-catalyzed hydroamination reaction of unactivated terminal olefins has been developed, providing a 62-fold rate increase over reactions compared to DTBM-SEGPHOS, the previous optimal ligand. Combining the respective strengths of computational chemistry and experimental kinetic measurements, we were able to quickly identify potential modifications that lead to more effective ligands, thus avoiding synthesizing and testing a large library of ligands. By optimizing the combination of attractive, noncovalent ligand-substrate interactions and the stability of the catalyst under the reaction conditions, we were able to identify a finely tuned hybrid ligand that greatly enables accelerated hydrocupration rates with unactivated alkenes. Moreover, a modular and robust synthetic sequence was devised, which allowed for the practical, gram-scale synthesis of these novel hybrid ligand structures.

Valorization of Biomass Derived Terpene Compounds by Catalytic Amination

This review fills an apparent gap existing in the literature by providing an overview of the readily available terpenes and existing catalytic protocols for preparation of terpene-derived amines. To address the role of solid catalysts in amination of terpenes the same reactions with homogeneous counterparts are also discussed. Such catalysts can be considered as a benchmark, which solid catalysts should match. Although catalytic systems based on transition metal complexes have been developed for synthesis of amines to a larger extent, there is an apparent need to reduce the production costs. Subsequently, homogenous systems based on cheaper metals operating by nucleophilic substitution (e.g., Ni, Co, Cu, Fe) with a possibility of easy recycling, as well as metal nanoparticles (e.g., Pd, Au) supported on amphoteric oxides should be developed. These catalysts will allow synthesis of amine derivatives of terpenes which have a broad range of applications as specialty chemicals (e.g., pesticides, surfactants, etc.) and pharmaceuticals. The review will be useful in selection and design of appropriate solid materials with tailored properties as efficient catalysts for amination of terpenes.

Intermolecular Hydroamination of 1,3-Dienes To Generate Homoallylic Amines

We report a Rh-catalyzed hydroamination of 1,3-dienes to generate homoallylic amines. Our work showcases the first case of anti-Markovnikov selectivity in the intermolecular coupling of amines and 1,3-dienes. By tuning the ligand properties and Brønsted acid additive, we find that a combination of rac-BINAP and mandelic acid is critical for achieving anti-Markovnikov selectivity.

Enantioselective Intermolecular Addition of Aliphatic Amines to Acyclic Dienes with a Pd-PHOX Catalyst

We report a method for the catalytic, enantioselective intermolecular addition of aliphatic amines to acyclic 1,3-dienes. In most cases, reactions proceed efficiently at or below room temperature in the presence of 5 mol % of a Pd catalyst bearing a PHOX ligand, generating allylic amines in up to 97:3 er. The presence of an electron-deficient phosphine within the ligand not only leads to a more active catalyst but also is critical for achieving high site selectivity in the transformation.

Rhodium-Catalyzed Hydrofunctionalization: Enantioselective Coupling of Indolines and 1,3-Dienes

We communicate a strategy for the hydrofunctionalization of 1,3-dienes via Rh-hydride catalysis. Conjugated dienes are coupled to nucleophiles to demonstrate the feasibility of novel C-C, C-O, C-S, and C-N bond forming processes. In the presence of a chiral JoSPOphos ligand, hydroamination generates chiral allylic amines with high regio- and enantioselectivity. Tuning both the pKa and steric properties of an acid-additive is critical for enantiocontrol.

An Efficient Amide-Aldehyde-Alkene Condensation: Synthesis for the N-Allyl Amides

The allylamine skeleton represents a significant class of biologically active nitrogen compounds that are found in various natural products and drugs with well-recognized pharmacological properties. In this personal account, we will briefly discuss the synthesis of allylamine skeletons. We will focus on showing a general protocol for Lewis acid-catalyzed N-allylation of electron-poor N-heterocyclic amides and sulfonamide via an amide-aldehyde-alkene condensation reaction. The substrate scope with respect to N-heterocyclic amides, aldehydes, and alkenes will be discussed. This method is also capable of preparing the Naftifine motif from N-methyl-1-naphthamide or methyl (naphthalene-1-ylmethyl)carbamate, with paraformaldehyde and styrene in a one-pot manner.

Anti-Markovnikov Hydroamination of Homoallylic Amines

The development of an anti-Markovnikov-selective hydroamination of unactivated alkenes is a significant challenge in organometallic chemistry. Herein, we present the rhodium-catalyzed anti-Markovnikov-selective hydroamination of homoallylic amines. The proximal Lewis basic amine serves to promote reactivity and enforce regioselectivity through the formation of the favored metallacycle, thus over-riding the inherent reactivity of the alkene. The scope of both the amine nucleophiles and homoallylic amines that participate in the reaction is demonstrated.

Enantioselective 1,2-Difunctionalization of Dienes Enabled by Chiral Palladium Complex-Catalyzed Cascade Arylation/Allylic Alkylation Reaction

A Pd-catalyzed highly enantioselective three-component coupling of 1,3-dienes with aryl iodines and sodium dialkyl malonates has been successfully established by using a H8-BINOL-based phosphoramidite ligand. This reaction proceeded via a Pd-catalyzed cascade arylation and asymmetric allylic alkylation reaction, providing an efficient strategy for the enantioselective 1,2-difunctionalization of 1,3-dienes.

P-stereogenic PNP pincer-Pd catalyzed intramolecular hydroamination of amino-1,3-dienes

A new P-stereogenic PNP pincer-Pd complex was readily prepared and was used in the asymmetric intramolecular hydroamination of amino-1,3-dienes, with the desired products being obtained in good yields and with excellent regioselectivities and up to moderate enantioselectivities.