A Simple, Broad-Scope Nickel(0) Precatalyst System for the Direct Amination of Allyl Alcohols

Nickel-Catalyzed Enantioconvergent Allenylic Amination of Allenols Activated by Hydrogen-Bonding Interaction with Methanol

The ubiquitous nature of amines in drug compounds, bioactive molecules and natural products has fueled intense interest in their synthesis. Herein, we introduce a nickel-catalyzed enantioconvergent allenylic amination of methanol-activated allenols. This protocol affords a diverse array of functionalized allenylic amines in high yields and with excellent enantioselectivities. The synthetic potential of this method is demonstrated by employing bioactive amines as nucleophiles and conducting gram-scale reactions. Furthermore, mechanistic investigations and DFT calculations elucidate the role of methanol as an activator in the nickel-catalyzed reaction, facilitating the oxidative addition of the C-O bond of allenols through hydrogen-bonding interactions. The remarkable outcomes arise from a rapid racemization of allenols enabled by the nickel catalyst and from highly enantioselective dynamic kinetic asymmetric transformation of η3-alkadienylnickel intermediates.

Primary Allylic Amine Synthesis via Pd-Catalyzed Direct Amination of Allylic Alcohols with Ammonium Acetate

Pd/DPEphos-catalyzed direct amination of allylic alcohols with readily available ammonium acetate as a nitrogen source provides access to convenient and scalable syntheses of primary allylic amines with high monoallylation selectivity. Mechanistic studies revealed that ammonium acetate functions as a Brønsted acid to activate the hydroxyl groups and inhibit overreaction.

Neutral nickel-catalyzed dehydrosulfonylation of unactivated allylic alcohols under mild conditions

Allyl sulfones are important sulfur-containing compounds that have widespread applications in organic synthesis, medicinal chemistry and materials science. Herein, nickel-catalysed dehydrosulfonylation of unactivated allyl alcohols with aryl sulfonyl hydrazides without additional active agents under mild conditions was developed. A variety of functional allyl sulfones could be efficiently synthesized in the presence of air-stable Ni(acac)2 as the catalyst and 1,1'-bis(diphenylphosphino)ferrocene (DPPF) as the ligand.

Practical synthesis of allylic amines via nickel-catalysed multicomponent coupling of alkenes, aldehydes, and amides

Molecules with an allylic amine motif provide access to important building blocks and versatile applications of biologically relevant chemical space. The need for diverse allylic amines requires the development of increasingly general and modular multicomponent reactions for allylic amine synthesis. Herein, we report an efficient catalytic multicomponent coupling reaction of simple alkenes, aldehydes, and amides by combining nickel catalysis and Lewis acid catalysis, thus providing a practical, environmentally friendly, and modular protocol to build architecturally complex and functionally diverse allylic amines in a single step. The method is remarkably simple, shows broad functional-group tolerance, and facilitates the synthesis of drug-like allylic amines that are not readily accessible by other methods. The utilization of accessible starting materials and inexpensive Ni(ii) salt as the alternative precatalyst offers a significant practical advantage. In addition, the practicality of the process was also demonstrated in an efficient, gram-scale preparation of the prostaglandin agonist.

Palladium-catalysed selective oxidative amination of olefins with Lewis basic amines

Amines are prominent in natural products, pharmaceutical agents and agrochemicals. Moreover, they are synthetically valuable building blocks for the construction of complex organic molecules and functional materials. However, amines, especially aliphatic and aromatic amines with free N-H bonds, tend to coordinate with transition metals and deactivate the catalyst, posing a tremendous challenge to applying Lewis basic amines in the amination of olefins. Here we present an example of oxidative amination of simple olefins with various Lewis basic amines. The combination of a palladium catalyst, 2,6-dimethyl-1,4-benzoquinone and a phosphorous ligand leads to the efficient synthesis of alkyl and aryl allylamines. A series of allylamines were obtained with good yields and excellent regio- and stereoselectivities. Intramolecular amination to synthesize tetrahydropyrrole and piperidine derivatives was also realized. Mechanistic investigations reveal that the reaction undergoes allylic C(sp³)-H activation and subsequent functionalization.

Biomacromolecule-Assisted Screening for Reaction Discovery and Catalyst Optimization

Reaction discovery and catalyst screening lie at the heart of synthetic organic chemistry. While there are efforts at de novo catalyst design using computation/artificial intelligence, at its core, synthetic chemistry is an experimental science. This review overviews biomacromolecule-assisted screening methods and the follow-on elaboration of chemistry so discovered. All three types of biomacromolecules discussed─enzymes, antibodies, and nucleic acids─have been used as "sensors" to provide a readout on product chirality exploiting their native chirality. Enzymatic sensing methods yield both UV-spectrophotometric and visible, colorimetric readouts. Antibody sensors provide direct fluorescent readout upon analyte binding in some cases or provide for cat-ELISA (Enzyme-Linked ImmunoSorbent Assay)-type readouts. DNA biomacromolecule-assisted screening allows for templation to facilitate reaction discovery, driving bimolecular reactions into a pseudo-unimolecular format. In addition, the ability to use DNA-encoded libraries permits the barcoding of reactants. All three types of biomacromolecule-based screens afford high sensitivity and selectivity. Among the chemical transformations discovered by enzymatic screening methods are the first Ni(0)-mediated asymmetric allylic amination and a new thiocyanopalladation/carbocyclization transformation in which both C-SCN and C-C bonds are fashioned sequentially. Cat-ELISA screening has identified new classes of sydnone-alkyne cycloadditions, and DNA-encoded screening has been exploited to uncover interesting oxidative Pd-mediated amido-alkyne/alkene coupling reactions.

Selective monoallylation of anilines to N-allyl anilines using reusable zirconium dioxide supported tungsten oxide solid catalyst

The monoallylation of aniline to give N-allyl aniline is a fundamental transformation process that results in various kinds of valuable building block allyl compounds, which can be used in the production of pharmaceuticals and electronic materials. For decades, sustainable syntheses have been gaining much attention, and the employment of allyl alcohol as an allyl source can follow the sustainability due to the formation of only water as a coproduct through dehydrative monoallylation. Although the use of homogeneous metal complex catalysts is a straightforward choice for the acceleration of dehydrative monoallylation, the use of soluble catalysts tends to contaminate products. We herein present a 10 wt% WO3/ZrO2 catalyzed monoallylation process of aniline to give N-allyl anilines in good yields with excellent selectivity, which enables the continuous selective flow syntheses of N-allyl aniline with 97-99% selectivity. The performed detailed study about the catalytic mechanism suggests that the dispersed WO3 with the preservation of the W(vi) oxidation state of 10 wt% WO3/ZrO2 with appropriate acidity and basicity is crucial for the monoallylation. The inhibition of the over allylation of the N-allyl anilines is explained by the unwilling contact of the N-allyl aniline with the active sites of WO3/ZrO2 due to the steric hindrance.

Diastereoselective construction of structurally diverse 2,3-dihydroquinolin-4-one scaffolds via redox neutral cascade [1,7]-hydride transfer/cyclization

The 2,3-dihydroquinolin-4-one scaffolds were constructed diastereoselectively via cascade Knoevengel condensation/[1,7]-HT/cyclization/transesterification featuring novel structures and diastereoselective construction of all-carbon quaternary centers.

Synthesis of medicinally relevant oxalylamines via copper/Lewis acid synergistic catalysis

Allylamines have long been recognized as valuable synthons because of their excellent reactivity in organic synthesis. Here, an efficient amination reaction of allenyl ethers via copper/Lewis acid synergistic catalysis has been established, providing straightforward access to diverse functionalized Z-oxalylamines and E -halogenated oxalylamines in good to excellent yields with high regio- and stereoselectivities. The developed method tolerates more than 100 examples that include late-stage functionalization of bioactive molecules, and features gram-scale synthesis of oxalylamines with high turnover number (TON > 1000) under mild and simple conditions. The applicability of the protocol is further demonstrated with the construction of drug molecules.

Catalytic Asymmetric Allylic Amination with Isatins, Sulfonamides, Imides, Amines, and N-Heterocycles

A generally useful palladium-catalyzed method for the asymmetric allylic amination with a large variety of isatins, sulfonamides, imides, amines, and N-heterocycles is introduced. A single protocol with a readily available catalyst accomplishes this reaction at room temperature with high yields and enantioselectivities often exceeding 90%, which is demonstrated with 31 examples.

General and selective synthesis of primary amines using Ni-based homogeneous catalysts

The development of base metal catalysts for industrially relevant amination and hydrogenation reactions by applying abundant and atom economical reagents continues to be important for the cost-effective and sustainable synthesis of amines which represent highly essential chemicals. In particular, the synthesis of primary amines is of central importance because these compounds serve as key precursors and central intermediates to produce value-added fine and bulk chemicals as well as pharmaceuticals, agrochemicals and materials. Here we report a Ni-triphos complex as the first Ni-based homogeneous catalyst for both reductive amination of carbonyl compounds with ammonia and hydrogenation of nitroarenes to prepare all kinds of primary amines. Remarkably, this Ni-complex enabled the synthesis of functionalized and structurally diverse benzylic, heterocyclic and aliphatic linear and branched primary amines as well as aromatic primary amines starting from inexpensive and easily accessible carbonyl compounds (aldehydes and ketones) and nitroarenes using ammonia and molecular hydrogen. This Ni-catalyzed reductive amination methodology has been applied for the amination of more complex pharmaceuticals and steroid derivatives. Detailed DFT computations have been performed for the Ni-triphos based reductive amination reaction, and they revealed that the overall reaction has an inner-sphere mechanism with H₂ metathesis as the rate-determining step.

A Ni-triphos based homogeneous catalyst enabled the synthesis of all kinds of primary amines by reductive amination of carbonyl compounds with ammonia and hydrogenation of nitroarenes.

Boron-Catalyzed N-Alkylation of Arylamines and Arylamides with Benzylic Alcohols

A sustainable boron-based catalytic approach for chemoselective N-alkylation of primary and secondary aromatic amines and amides with primary, secondary, and tertiary benzylic alcohols has been presented. The metal-free protocol operates at low catalyst loading, tolerates several functional groups, and generates H₂O as the sole byproduct. Preliminary mechanistic studies were performed to demonstrate the crucial role of boron catalyst for the activation of the intermediate dibenzyl ether and to identify the rate-determining step.

Nickel-Catalyzed Selective Reduction of Carboxylic Acids to Aldehydes

The direct reduction of carboxylic acids to aldehydes is a fundamental transformation in organic synthesis. The combination of an air-stable Ni precatalyst, dimethyl dicarbonate as an activator, and silane reductant effects this reduction for a wide variety of substrates, including pharmaceutically relevant structures, in good yields and with no overreduction to alcohols. Moreover, this methodology is scalable, allows access to deuterated aldehydes, and is also compatible with one-pot utilization of the aldehyde products.

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.