Transition-Metal-Free Regioselective Intermolecular Hydroamination of Conjugated 1,3-Dienes with Heterocyclic Amines

Palladium-Catalyzed N-Allylic Alkylation of Pyrazoles and Unactivated Vinylcyclopropanes

An efficient palladium-catalyzed N-allylic alkylation of pyrazoles and unactivated vinylcyclopropanes is demonstrated, affording various N-alkyl pyrazoles in ≤99% yield. This protocol displays high atom economy, a broad range of substrates, and excellent regioselectivity and stereoselectivity. Late-stage modification of bioactive molecules, scaled-up reaction, and divergent derivatization documented the practicability of this methodology. The preliminary mechanistic investigation hinted that the Pd-H species promotes the ring opening of cyclopropanes.

Kinetic Resolution of N-Allylic Pyrazoles via Photoexcited Chiral Copper Complex-Catalyzed Alkene E → Z Isomerization

Herein, we present an efficient and practical kinetic resolution (KR) of racemic allylic pyrazoles utilizing photoexcited chiral-copper-complex-mediated alkene E → Z isomerization. This method enables the synthesis of both enantioenriched E- and Z-allylic pyrazoles, achieving enantiomeric excesses (e.e.) of up to 97% and selectivity factors (S factors) as high as 217. Remarkably, the method's ability to furnish allylic pyrazoles with the Z-configuration, which is notably arduous to obtain under thermodynamic control, underscores the transformative potential of this synthetic protocol.

Hydro-phosphorothiolation of Styrene and Cyclopropane with S-Hydrogen Phosphorothioates under Ambient Conditions

A metal-free hexafluoroisopropanol-mediated hydro-phosphorothiolation of styrenes and donor-acceptor cyclopropanes with S-hydrogen phosphorothioates in a Markovnikov fashion has been developed under ambient reaction conditions to afford a library of S-alkyl phosphorothioates. Notably, this strategy provides a simple and efficient way to produce biologically significant kitazin and iprobenfos derivatives. Mechanistic studies disclose that the reaction proceeds through a carbocation intermediate.

Acetate Assistance in Regioselective Hydroamination of Allenamides: A Combined Experimental and Density Functional Theory Study

A key factor in the development of selective nucleophilic addition to allenamides is controlling the reactivity of electrophilic intermediates, which is generally achieved using an electrophilic activator via conjugated iminium intermediates. In this combined experimental and computational study, we show that a general and highly chemoselective hydroamination of allenamides can be accomplished using a combination of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and NaOAc. Experimental mechanistic studies revealed that HFIP mediates proton transfer to activate the allenamide, while the acetate additive significantly contributes to N-selective interception. This strategy enables a general hydroamination of allenamides without the use of metals. We demonstrated that various functionalized 1,3-diamines could be readily synthesized and diversified into value-added structural motifs. Detailed mechanistic investigations using the density functional theory revealed the role of NaOAc in the formation of reactive electrophilic intermediates, which ultimately governed the selective formation of 1,3-diamine products. Critically, calculations of the potential energy surface around the proton-transfer transition state revealed that two different reactive electrophilic intermediates were formed when NaOAc was added.

Phosphoric Acid Catalyzed N-Addition/ C-Addition Reaction of 3-Vinyl Indoles with Pyrazole/Pyrazolone to Construct Pyrazole-Substituted 3-(1-Heteroarylethyl)-indole Scaffolds

Developing a highly efficient atom-economic method for the preparation of 3-(1-heteroarylethyl)-indole scaffolds is of significant value in pharmaceutical and agricultural chemistry. Herein, a phosphoric acid-catalyzed N-addition reaction of 3-vinyl indoles with pyrazoles and C-addition reaction of 3-vinyl indoles with pyrazolones were developed. A series of pyrazole-substituted 3-(1-heteroarylethyl)-indole scaffolds were synthesized in excellent yields (up to 99% yield) under mild reaction conditions. A reasonable reaction mechanism was proposed to explain the experimental results.

An Intermolecular Hydroarylation of Unactivated Arylcyclopropane via Re2O7/HFIP-Mediated Ring Opening

In this paper, we describe a Re2O7-mediated ring-opening arylation of unactivated arylcyclopropane because of its functionalization with various arenes via Friedel-Crafts-type reactivity. This protocol allows facile access to functionalized 1,1-diaryl alkanes and is characterized by a broad substrate scope, mild reaction conditions, high efficiency, and high atom economy. Both density functional theory calculations and deuterium labeling experiments were carried out to justify the indispensable role of HFIP in this transformation and pointed to Re2O7-mediated ring opening being the rate-determining step.

Route to Functionalized Tetrahydrobenzo[d]azepines via Re2O7-Mediated Intramolecular Friedel-Crafts Reaction

We describe a Re2O7-mediated intramolecular dehydrative Friedel-Crafts reaction for the efficient synthesis of various benzo-fused heterocycles such as benzazepines and benzazocines. This process is characterized by a broad substrate scope, mild reaction conditions, high efficiency, and high atom economy. The potential application of this methodology was exemplified by the facile preparation of a NMDA antagonist as well as a key intermediate en route to SKF 38393.

Iso-Pentadienyl Carbonate as a Five Carbon Synthon in Manganese(I)-Catalyzed Selective Linear 1,3-Dienylation

Selective linear 1,3-dienylations are essential transformations, and numerous synthetic efforts have been documented. However, a general method enabling access to electron-rich, -poor, and biologically relevant dienyl molecules is in high demand. Hence, we report a straightforward method of manganese(I)-catalyzed C-H dienylation of arenes by using iso-pentadienyl carbonate as a five carbon synthon. This is a highly unprecedented report for selective linear 1,3-dienylation using manganese C-H activation catalysis. Our method facilitates the synthesis of varieties of dienes, including those suitable for normal or inverse electron demand Diels-Alder reactions, dienyl glycoconjugates, and unnatural amino acids. Extensive mechanistic studies, including isolation of C-H activated organo-manganese complex and isotopic analyses, have supported the proposed mechanism of this dienylation. The synthetic applicability of this method eased to deliver a 6/6/5-fused tricyclic nagilactone scaffold.

Synthesis of 1-Aryltetralins via Re2O7/HReO4 Mediated Intramolecular Hydroarylations

Here, we describe highly efficient intramolecular hydroarylations mediated by Re2O7/HReO4. Styrene derivatives of different electronic properties have been activated to effect a challenging intramolecular hydroarylation for the facile access to various substituted 1-aryltetralin structures. This method is characterized by mild reaction conditions, broad substrate scope, high chemical yields, and 100% atom economy. The potential synthetic application of this methodology was exemplified by the efficient total synthesis of an isoCA-4 analogue.

Progression of Hydroamination Catalyzed by Late Transition-Metal Complexes from Activated to Unactivated Alkenes

ConspectusCatalytic intermolecular hydroamination of alkenes is an atom- and step-economical method for the synthesis of amines, which have important applications as pharmaceuticals, agrochemicals, catalysts, and materials. However, hydroaminations of alkenes in high yield with high selectivity are challenging to achieve because these reactions often lack a thermodynamic driving force and often are accompanied by side reactions, such as alkene isomerization, telomerization, and oxidative amination. Consequently, early examples of hydroamination were generally limited to the additions of N-H bonds to conjugated alkenes or strained alkenes, and the catalytic hydroamination of unactivated alkenes with late transition metals has only been disclosed recently. Many classes of catalysts, including early transition metals, late transition metals, rare-earth metals, acids, and photocatalysts, have been reported for catalytic hydroamination. Among them, late transition-metal complexes possess several advantages, including their relative ease of handling and their high compatibility of substrates containing polar or sensitive functional groups.This Account describes the progression in our laboratory of hydroaminations catalyzed by late transition-metal complexes from the initial additions of N-H bonds to activated alkenes to the more recent additions to unactivated alkenes. Our developments include the Markovnikov and anti-Markovnikov hydroamination of vinylarenes with palladium, rhodium, and ruthenium, the hydroamination of dienes and trienes with nickel and palladium, the hydroanimation of bicyclic strained alkenes with neutral iridium, and the hydroamination of unactivated terminal and internal alkenes with cationic iridium and ruthenium. Enantioselective hydroaminations of these classes of alkenes to form enantioenriched, chiral amines also have been developed.Mechanistic studies have elucidated the elementary steps and the turnover-limiting steps of these catalytic reactions. The hydroamination of conjugated alkenes catalyzed by palladium, rhodium, nickel, and ruthenium occurs by turnover-limiting nucleophilic attack of the amine on a coordinated benzyl, allyl, alkene, or arene ligand. On the other hand, the hydroamination of unconjugated alkenes catalyzed by ruthenium and iridium occurs by turnover-limiting migratory insertion of the alkene into a metal-nitrogen bond. In addition, pathways for the formation of side products, including isomeric alkenes and enamines, have been identified during our studies. During studies on enantioselective hydroamination, the reversibility of the hydroamination has been shown to erode the enantiopurity of the products. Based on our mechanistic understandings, new generations of catalysts that promote catalytic hydroaminations with higher rates, chemoselectivity, and enantioselectivity have been developed. We hope that our discoveries and mechanistic insights will facilitate the further development of catalysts that promote selective, practical, and efficient hydroamination of alkenes.

Three-Component Electrochemical Aminoselenation of 1,3-Dienes

Azoles and organoselenium compounds are pharmacologically important scaffolds in medicinal chemistry and natural products. We developed an efficient regioselective electrochemical aminoselenation reaction of 1,3-dienes, azoles, and diselenide derivatives to access selenium-containing allylazoles skeletons. This protocol is more economical and environmentally friendly and features a broad substrate scope; pyrazole, triazole, and tetrazolium were all tolerated under the standard conditions, which could be applied to the expedient synthesis of bioactive molecules and in the pharmaceutical industry.

Re2O7/HReO4 Mediated Intramolecular Hydroacyloxylation of Unactivated Alkenes: A Dual Hydrogen-Bonding Effect

This publication describes the application of Re₂O₇ in hexafluoroisopropanol (HFIP) for the activation of inert as well as electronically deactivated olefins to facilitate a challenging intramolecular hydroacyloxylation reaction. Both HFIP and an internal carboxy group have been proven to be crucial for the successful implementation of this transformation; these are proposed to assist the formation and stabilization of the key cationic intermediate via hydrogen-bonding interactions with perrhenate anion (ReO₄^-).

Nickel-Catalyzed Hydroarylation Reaction: A Useful Tool in Organic Synthesis

This article describes the recent advances in the field of nickel-catalyzed hydroarylation reaction of alkenes, alkynes, and arenes. All reactions proceeded either through internal hydride transfer or in presence of...