Catalytic Reductive Functionalization of Tertiary Amides using Vaska’s Complex: Synthesis of Complex Tertiary Amine Building Blocks and Natural Products

Catalytic Reductive Amination and Tandem Amination-Alkylation of Esters Enabled by a Cationic Iridium Complex

Reported herein is a convenient and efficient method for one-pot, catalytic reductive amination, as well as the first multi-component tandem reductive amination-functionalization of bench-stable and readily available common carboxylic esters. This method is based on the cationic [Ir(COD)2]BArF-catalyzed chemoselective hydrosilylation of esters, followed by one-pot acid-mediated amination and nucleophilic addition. The reaction was conducted under mild conditions at a very low catalyst loading (0.1 mol % of Ir), which could be further reduced to 0.001 mol %, as demonstrated by a reaction at a 15 g scale. The method is highly versatile, allowing the use of esters with or without α-protons for the N-mono-alkylation of primary and secondary amines to produce diverse secondary and tertiary amines, as well as α-branched/functionalized amines. The method is highly chemoselective and tolerates a variety of functional groups such as bromo, trifluoromethyl, ester, and cyano groups. The value of the method was demonstrated by the one-step catalytic synthesis of two bio-relevant N-mono-methyl α-amino esters and the antiparkinsonian agent piribedil, as well as by the use of two shorter chain triglycerides as alkylating feedstock.

Machine learning directed discovery and optimisation of a platinum-catalysed amide reduction

The discovery and optimisation of reaction conditions leading to the reduction of amides, a fundamental large-scale industrial reaction, is achieved using a machine learning (ML) platform and a platinum catalyst. The optimisation leads to the discovery of a new platinum-based catalytic system that displays unexpectedly high performance. The approach enables rapid and high conversions at ppm-level catalyst loadings.

The Latest Progress in the Chemistry of Daphniphyllum Alkaloids

Daphniphyllum alkaloids (DAs) are interesting molecules with rich molecular skeletons and diverse biological activities. Since their discovery, phytochemists have isolated, purified, and identified more than 350 DAs. Synthetic chemists, attracted by the structure and activity of DAs, have accomplished many elegant synthetic jobs. Herein, we summarize work on the isolation, structural identification, bioactivity testing, and synthesis of DAs from 2018 to 2023, with the aim of providing a reference for future studies.

Enantioselective Deoxygenative Amino-Cyanation of Carboxylic Acids via Ti-Multicatalysis

Carboxylic acids are valued synthetic building blocks that offer shelf life stability, structural diversity, and wide commercial availability. Despite the remarkable synthetic utility of carboxylic acids, a direct enantioselective deoxygenative functionalization of carboxylic acids remains rare. We present enantioselective deoxygenative amino-cyanation of carboxylic acids using a novel TiIV-multicatalytic system that catalytically modified each C-O bond of carboxylic acid to C-C, C-N, and C-H bonds, generating enantio-enriched chiral α-amino nitriles (up to 98:2 er).

Deoxygenative Geminal Silylboration of Amides Using Silylboronates: Synthesis and Use of α-Boryl-α-Silylalkylamines

α-Silylalkylamines and α-borylalkylamines are versatile synthetic intermediates and attractive scaffolds found in pharmaceutical drugs and agrochemicals. Despite great progress on synthetic methods for preparation of α-silylalkylamines or α-borylalkylamines, there are no general strategies for preparation of α-boryl-α-silylalkylamines and the reactivity has not been explored. Here we report deoxygenative geminal silylboration of amides using silylboronates in the presence of alkoxide base catalyst, producing α-boryl-α-silylalkylamines. The silicon and boron groups in α-boryl-α-silylalkylamines are found to be utilized to chemoselective transformations, such as protonation and alkylation. This protocol serves various α-silylalkylamines and α-borylalkylamines from readily available amides.

Catalytic Asymmetric Synthesis of Bicyclic Isothioureas from a Common Enolizable Template

While bicyclic isothiourea (ITU) moieties are found in biologically active molecules and organocatalysts, a catalytic asymmetric synthesis of ITUs is pending. Here, we report the catalytic, enantioselective functionalization of enolizable template II with a variety of electrophiles, including unsaturated ketones, esters, sulfones, nitro compounds, and thiolating reagents, as an entry to enantioenriched bicyclic ITUs III. Scope and limitations are shown, as well as examples of product derivatization.

Organocatalytic Deoxygenative [3+2] Cycloaddition of N-Hydroxyamides with Alkynes to Access Isoxazoles

Although the transition-metal-catalyzed [3+2] cycloadditions to access isoxazoles have been described well, organocatalytic methods remain underdeveloped. Herein, we report the use of an organophosphine catalyst for the preparation of a series of isoxazoles with exceptional regioselectivity via the [3+2] cycloaddition of N-hydroxyamides and alkynes. The scope of this organocatalytic transformation is broad, tolerating numerous functional groups and proceeding uniformly in an environmentally friendly, simple, and efficient manner.

Deoxygenative alkynylation of amides via CO bond cleavage

A novel deoxygenative alkynylation of amides promoted by a synergistic action of a divalent rare-earth element and a transition metal has been developed. In this method, α-alkynyl substituted amines are synthesized from unactivated amides and alkynes in a single transformation. Broad substrate scope and excellent selectivity for CO cleavage has been demonstrated. This approach represents a general method for the construction of versatile α-alkynyl substituted amines from unactivated amide bonds.

A Type of Stable Amides Behaves as Acyl Transfer Reagents upon Visible-Light Irradiation through Self-Aromatization

Organic molecules with light-modifiable reactivity are important in many fields because they can serve as the "switch" for light to trigger chemical processes. Herein, we disclose a new type of stable non-twisted amides, the reactivity of which can be turned on by light as acyl transfer reagents. Upon photo-activation, these amides react with various nucleophiles including amines, phenols, hydroxide, thiols, boronic acids, and alkynes either under metal-free or metal-catalysis conditions. This reactivity hinges on the design and synthesis of a photo-activatable reagent (7-nitro-5,6-dihydrophenanthridine), which undergoes self-aromatization enabled by an internal oxidant under light. This masked acyl donor group is anticipated to be useful in scenarios where light is preferred to trigger a chemical process.

Making Full Use of TMSCF3: Deoxygenative Trifluoromethylation/Silylation of Amides

As one of the most powerful trifluoromethylation reagents, (trifluoromethyl)trimethylsilane (TMSCF3) has been widely used for the synthesis of fluorine-containing molecules. However, to the best of our knowledge, the simultaneous incorporation of both TMS- and CF3- groups of this reagent onto the same carbon of the products has not been realized. Herein, we report an unprecedented SmI2/Sm promoted deoxygenative difunctionalization of amides with TMSCF3, in which both silyl and trifluoromethyl groups are incorporated into the final product, yielding α-silyl-α-trifluoromethyl amines with high efficiency. Notably, the silyl group could be further transformed into other functional groups, providing a new method for the synthesis of α-quaternary α-CF3-amines.

Counterintuitive chemoselectivity in the reduction of carbonyl compounds

The reactivity of carbonyl functional groups largely depends on the substituents on the carbon atom. Reversal of the commonly accepted order of reactivity of different carbonyl compounds requires novel synthetic approaches. Achieving selective reduction will enable the transformation of carbon resources such as plastic waste, carbon dioxide and biomass into valuable chemicals. In this Review, we explore the reduction of less reactive carbonyl groups in the presence of those typically considered more reactive. We discuss reductions, including the controlled reduction of ureas, amides and esters to aldehydes, as well as chemoselective reductions of carbonyl groups, including the reduction of ureas over carbamates, amides and esters; the reduction of amides over esters, ketones and aldehydes; and the reduction of ketones over aldehydes.

Deoxy-Arylation of Amides via a Tandem Hydrosilylation/Radical- Radical Coupling Sequence

Vaska's complex is a prominent catalyst for the hydrosilylation of amides. The O-silyl hemiaminal intermediate formed in these processes has been demonstrated as an electrophile for nucleophilic additions. More recently, these intermediates have been shown to be suitable for single electron reduction to generate α-amino radicals. Leveraging the ability to generate α-amino radicals from these hemiaminals, we describe a two-step, one-pot, deoxy-arylation of amides utilizing iridium-catalyzed hydrosilylation and photoredox catalysis. This transformation can be tailored toward the late-stage functionalization of biologically relevant molecules, with drug discovery applications as shown in the streamlined synthesis of an NPY Y2 inhibitor.

Stereodivergent synthesis of 2-oxo-oligopyrrolidines by an iterative coupling strategy

Natural linear polyamines play diverse roles in physiological processes by interacting with receptors at the cellular level. Herein, we describe the stereodivergent synthesis of oligopyrrolidines, which are conformationally constrained polyamines. We synthesized dimeric and trimeric 2-oxo-oligopyrrolidines using an iterative coupling strategy. The key to our success is an iridium-catalyzed trans/cis-selective nucleophilic addition and subsequent threo/erythro-stereoselective reduction. The synthesized pyrrolidines show varying cytotoxicities against a human cancer cell line depending on the number of rings and their stereochemistry.

Fully Automated Flow Protocol for C(sp3)-C(sp3) Bond Formation from Tertiary Amides and Alkyl Halides

Herein, we present a novel C(sp3)-C(sp3) bond-forming protocol via the reductive coupling of abundant tertiary amides with organozinc reagents prepared in situ from their corresponding alkyl halides. Using a multistep fully automated flow protocol, this reaction could be used for both library synthesis and target molecule synthesis on the gram-scale starting from bench-stable reagents. Additionally, excellent chemoselectivity and functional group tolerance make it ideal for late-stage diversification of druglike molecules.

Multicomponent Synthesis of α-Branched Amines via a Zinc-Mediated Carbonyl Alkylative Amination Reaction

Methods for the synthesis of α-branched alkylamines are important due to their ubiquity in biologically active molecules. Despite the development of many methods for amine preparation, C(sp3)-rich nitrogen-containing compounds continue to pose challenges for synthesis. While carbonyl reductive amination (CRA) between ketones and alkylamines is the cornerstone method for α-branched alkylamine synthesis, it is sometimes limited by the sterically demanding condensation step between dialkyl ketones and amines and the more restricted availability of ketones compared to aldehydes. We recently reported a "higher-order" variant of this transformation, carbonyl alkylative amination (CAA), which utilized a halogen atom transfer (XAT)-mediated radical mechanism, enabling the streamlined synthesis of complex α-branched alkylamines. Despite the efficacy of this visible-light-driven approach, it displayed scalability issues, and competitive reductive amination was a problem for certain substrate classes, limiting applicability. Here, we report a change in the reaction regime that expands the CAA platform through the realization of an extremely broad zinc-mediated CAA reaction. This new strategy enabled elimination of competitive CRA, simplified purification, and improved reaction scope. Furthermore, this new reaction harnessed carboxylic acid derivatives as alkyl donors and facilitated the synthesis of α-trialkyl tertiary amines, which cannot be accessed via CRA. This Zn-mediated CAA reaction can be carried out at a variety of scales, from a 10 μmol setup in microtiter plates enabling high-throughput experimentation, to the gram-scale synthesis of medicinally-relevant compounds. We believe that this transformation enables robust, efficient, and economical access to α-branched alkylamines and provides a viable alternative to the current benchmark methods.

Asymmetric Deoxygenative Functionalization of Secondary Amides with Vinylpyridines Enabled by a Triple Iridium-Photoredox-Chiral Phosphoric Acid System

An enantioselective deoxygenative functionalization of secondary amides with vinylpridines is developed by merging relay iridium catalysis and cooperative photoredox-chiral Brønsted acid catalysis, affording a series of valuable chiral amines in moderate to good yields with good enantioselectivities. The intriguing multiple catalytic system invoking triple-catalysis was found to be the key to the success of the current reactions, which may stimulate further development of catalytic methodologies for asymmetric deoxygenative transformations of amides.

Iridium-Catalyzed Reductive (3+2) Annulation of Lactams Enabling the Rapid Total Synthesis of (±)-Eburnamonine

A reductive (3+2) annulation of lactams through iridium-catalyzed hydrosilylation and photoredox coupling with α-bromoacetic acid was developed. The iridium-catalyzed hydrosilylation of the lactam carbonyl group and subsequent elimination provide a transient cyclic enamine, which undergoes iridium-catalyzed photoredox coupling with α-bromoacetic acid in a one-pot process. The developed conditions show high functional-group tolerance and provide cyclic N,O-acetals containing a quaternary carbon center. The resulting N,O-acetals undergo a variety of acid-mediated nucleophilic addition reactions via iminium ions to give substituted cyclic amines. The developed sequence including reductive (3+2) annulation and acid-mediated nucleophilic addition was successfully applied to the four-step total synthesis of (±)-eburnamonine.

Asymmetric Synthesis of Arboduridine

The first asymmetric total synthesis of the monoterpenoid indole alkaloid arboduridine has been accomplished. The tricyclic A/B/D ring system was constructed by an enantioselective Michael reaction followed by intramolecular nucleophilic addition. Intramolecular α-amination of a ketone forged the piperidine ring, while a Horner-Wadsworth-Emmons (HWE) reaction was used to form the pyrrolidine ring. A reduction cyclization cascade led to formation of the tetrahydrofuran ring.

Enantioselective Total Synthesis of (+)-Incargranine A Enabled by Bifunctional Iminophosphorane and Iridium Catalysis

Herein we report the first enantioselective total synthesis of (+)-incargranine A, in nine steps. The total synthesis was enabled by an enantioselective intramolecular organocatalysed desymmetrising Michael addition of a malonamate ester to a linked dienone substrate that established pivotal stereocentres with excellent enantio- and complete diastereoselectivity. Furthermore, a key hemiaminal intermediate was accessed by developing an iridium-catalysed reductive cyclisation, and the scope of this transformation was explored to produce a range of bicyclic hemiaminal motifs. Once installed, the hemiaminal motif was used to initiate a biomimetic cascade to access the natural product directly in a single step.

1,2-Redox Transpositions of Tertiary Amides

Reactions capable of transposing the oxidation levels of adjacent carbon atoms enable rapid and fundamental alteration of a molecule's reactivity. Herein, we report the 1,2-transposition of the carbon atom oxidation level in cyclic and acyclic tertiary amides, resulting in the one-pot synthesis of 1,2- and 1,3-oxygenated tertiary amines. This oxidation level transfer was facilitated by the careful orchestration of an iridium-catalyzed reduction with the functionalization of transiently formed enamine intermediates. A novel 1,2-carbonyl transposition is described, and the breadth of this redox transposition strategy has been further explored by the development of aminoalcohol and enaminone syntheses. The diverse β-functionalized amine products were shown to be multifaceted and valuable synthetic intermediates, accessing challenging biologically relevant motifs.

Catalytic enantioselective reductive alkynylation of amides enables one-pot syntheses of pyrrolidine, piperidine and indolizidine alkaloids

The primary objective in synthetic organic chemistry is to develop highly efficient, selective, and versatile synthetic methodologies, which are essential for discovering new drug candidates and agrochemicals. In this study, we present a unified strategy for a one-pot, catalytic enantioselective synthesis of α-alkyl and α,α'-dialkyl pyrrolidine, piperidine, and indolizidine alkaloids using readily available amides and alkynes. This synthesis is enabled by the identification and development of an Ir/Cu/N-PINAP catalyzed highly enantioselective and chemoselective reductive alkynylation of α-unbranched aliphatic amides, which serves as the key reaction. This reaction is combined with Pd-catalyzed tandem reactions in a one-pot approach, enabling the collective, catalytic enantioselective total syntheses of eight alkaloids and an anticancer antipode with 90-98% ee. The methodology's enantio-divergence is exemplified by the one-step access to either enantiomer of alkaloid bgugaine.

Streamlined Strategy for Scalable and Enantioselective Total Syntheses of the Eburnane Alkaloids

A general, concise, and efficient strategy for the enantioselective synthesis of the eburnane alkaloid family of natural products is disclosed. Specifically, 13 members of the natural product family were prepared from commercially available and inexpensive starting materials. The brevity and modularity of the route are largely on account of a two-phase synthesis logic and a key catalytic enantioconvergent cross-coupling to establish the C20 stereogenic center. The strategies described here are expected to facilitate in-depth biological studies and provide access to new anticancer eburnane analogues.

Reactivity Umpolung of Tertiary Amide Enabled by Catalytic Reductive Stannylation

Reactivity umpolung is an important concept in organic chemistry. Established reactivity umpolung mainly focuses on the aldehyde and umpolung of amide carbonyl group is not known. In this report, we describe a process to obtain the umpolung reactivity of tertiary amide. This process hinges on the efficient reductive stannylation catalyzed by Ir/silane and facile Sn-Li exchange. By leveraging this umpolung reactivity, drug Fluoxetine was derivatized to 12 different analogues via reacting with various electrophiles and four biologically active molecules were prepared concisely. This unlocked umpolung reactivity of tertiary amide is expected to find applications to synthesize complex amines from amides.

Preparation of 3,5-Methanobenzo[b]azepines: An sp3-Rich Quinolone Isostere

The replacement of the aromatic ring in bioactive compounds with saturated bioisosteres has become a popular tactic to obtain novel structures with improved physicochemical profiles. In this paper, we describe an efficient synthesis of 3,5-methanobenzo[b]azepine analogues and suggest them as isosteres of quinolones. Quinolones are heteroaromatic, flat rings and considered as privileged scaffolds. An isosteric version of this scaffold with more 3D character would offer new options to expand their use.

Rapid Access to 2,2-Disubstituted Indolines via Dearomative Indolic-Claisen Rearrangement: Concise, Enantioselective Total Synthesis of (+)-Hinckdentine A

The construction of 2,2-disubstituted indolines has long presented a synthetic challenge without any general solutions. Herein, we report a robust protocol for the dearomative Meerwein-Eschenmoser-Claisen rearrangement of 3-indolyl alcohols that provides efficient access to 2-substituted and 2,2-disubstituted indolines. These versatile subunits are useful for natural product synthesis and medicinal chemistry. The title [3,3] sigmatropic rearrangement proceeds in generally excellent yield and transfers the C3-indolic alcohol chirality to the C2 position with high fidelity, thus providing a reliable method for the construction of enantioenriched 2,2-disubstituted indolines. The power of this methodology is demonstrated through the concise and strategically unique total synthesis of the marine natural product hinckdentine A, which features a dearomative Claisen rearrangement, a diastereocontrolled hydrogenation of the alkene product, a one-pot amide-to-oxime conversion using Vaska's complex, and a regioselective late-stage tribromination.

Mild Divergent Semireductive Transformations of Secondary and Tertiary Amides via Zirconocene Hydride Catalysis

The mild catalytic partial reduction of amides to imines has proven to be a challenging synthetic transformation, with many transition metals directly reducing these substrates to amines. Herein, we report a mild, catalytic method for the semireduction of both secondary and tertiary amides via zirconocene hydride catalysis. Utilizing just 5 mol % of Cp2ZrCl2, the reductive deoxygenation of secondary amides is demonstrated to furnish a diverse array of imines in up to 94% yield with excellent chemoselectivity and without the need for glovebox handling. Moreover, a novel reductive transamination of tertiary amides is also achievable when the catalytic protocol is carried out in the presence of a primary amine at room temperature, providing access to an expanded assortment of imines in up to 98% yield. Through slight procedural tuning, the single-flask conversion of amides to imines, aldehydes, amines or enamines is feasible, including multicomponent syntheses.

Total Synthesis of Vilmoraconitine

Vilmoraconitine belongs to one of the most complex skeleton types in the C19-diterpenoid alkaloids, which architecturally features an unprecedented heptacyclic core possessing a rigid cyclopropane unit. Here, we report the first total synthesis of vilmoraconitine relying on strategic use of efficient ring-forming reactions. Key steps include an oxidative dearomatization-induced Diels-Alder cycloaddition, a hydrodealkenylative fragmentation/Mannich sequence, and an intramolecular Diels-Alder cycloaddition.

Total synthesis of the natural (-)-205B alkaloid and its activity toward α7 nAChRs

A new approach to the synthesis of the (-)-205B alkaloid is described in this paper. This work is characterised by the development of an efficient chirality transfer through a silyl tethered intramolecular alkylation reaction, an unprecedented tandem highly selective iridium catalyzed partial reduction of lactam coupled with an acid promoted aza-Prins reaction, and an almost complete stereochemical control in Shenvi's radical hydrogen atom transfer on an exocyclic methylene. The second part of this work demonstrates the positive allosteric behavior of this natural alkaloid toward α7 nAChRs, in contrast to the reported inhibitory effect of the unnatural enantiomer.

Asymmetric Total Synthesis of Hasubanan Alkaloids: Periglaucines A-C, N,O-Dimethyloxostephine and Oxostephabenine

We report herein the asymmetric total synthesis of periglaucines A-C, N,O-dimethyloxostephine and oxostephabenine. The key strategies used include: 1) a Rh^I -catalyzed regio- and diastereoselective Hayashi-Miyaura reaction to connect two necessary fragments; 2) an intramolecular photoenolization/Diels-Alder (PEDA) reaction to construct the highly functionalized tricyclic core skeleton bearing a quaternary center; 3) a bio-inspired intramolecular Michael addition and transannular acetalization to generate the aza[4.4.3]propellane and the tetrahydrofuran ring.

α-Aminocarbene-Mediated Si-H Insertion: Deoxygenative Silylation of Aromatic Amides with Silanes

While metal carbene-mediated Si-H insertion reactions have become a powerful strategy to build new C-Si bonds, the utilization of α-aminocarbene intermediates generated from readily available precursors in the Si-H insertion reaction remains a longstanding challenge. Herein, we develop a practical and general strategy to synthesize α-aminosilanes through a deoxygenative cross-coupling of amides and silanes mediated by Sm/SmI₂. Given the simplicity and versatility, this methodology represents a fascinating example for the effective utilization of inert amides as α-aminocarbene precursors in organic synthesis.

Tertiary Amides as Fluoroalkyl Aldehyde Surrogates: Access to meso-Fluorinated Bis(heteroaryl)methanes

Tertiary, morpholine-derived, fluoroalkyl amides have been found to be efficient, readily accessible, bench-stable surrogates of fluoroalkyl aldehydes. This discovery is applied to the one-pot synthesis of a symmetrical and, more challengingly, unsymmetrical meso-fluoroalkylated bis(heteroaryl)methanes via a Schwartz's reagent-mediated reductive activation. The usefulness of this approach for the introduction of a fluoromethylated carbon bridge was proven by implementation of the developed methodology in the synthesis of a fluorine-decorated bispyrromethane skeleton and an α-alkylated BODIPY core.

Challenges and Breakthroughs in Selective Amide Activation

In contrast to ketones and carboxylic esters, amides are classically seen as comparatively unreactive members of the carbonyl family, owing to their unique structural and electronic features. However, recent decades have seen the emergence of research programmes focused on the selective activation of amides under mild conditions. In the past four years, this area has continued to rapidly develop, with new advances coming in at a fast pace. Several novel activation strategies have been demonstrated as effective tools for selective amide activation, enabling transformations that are at once synthetically useful and mechanistically intriguing. This Minireview comprises recent advances in the field, highlighting new trends and breakthroughs in what could be called a new age of amide activation.

Challenges and Breakthroughs in Selective Amide Activation

In contrast to ketones and carboxylic esters, amides are classically seen as comparatively unreactive members of the carbonyl family, owing to their unique structural and electronic features. However, recent decades have seen the emergence of research programmes focused on the selective activation of amides under mild conditions. In the past four years, this area has continued to rapidly develop, with new advances coming in at a fast pace. Several novel activation strategies have been demonstrated as effective tools for selective amide activation, enabling transformations that are at once synthetically useful and mechanistically intriguing. This Minireview comprises recent advances in the field, highlighting new trends and breakthroughs in what could be called a new age of amide activation.

Multicatalysis protocol enables direct and versatile enantioselective reductive transformations of secondary amides

The catalytic asymmetric geminal bis-nucleophilic addition to nonreactive functional groups is a type of highly desirable yet challenging transformation in organic chemistry. Here, we report the first catalytic asymmetric reductive/deoxygenative alkynylation of secondary amides. The method is based on a multicatalysis strategy that merges iridium/copper relay catalysis with organocatalysis. A further combination with the palladium-catalyzed alkyne hydrogenation allows the one-pot enantioselective reductive alkylation of secondary amides. This versatile protocol allows the efficient synthesis of four types of α-branched chiral amines, which are prevalent structural motifs of active pharmaceutical ingredients. The protocol also features excellent enantioselectivity, chemoselectivity, and functional group tolerance to be compatible with more reactive functional groups such as ketone and aldehyde. The synthetic utility of the method was further demonstrated by the late-stage functionalization of two drug derivatives and the concise, first catalytic asymmetric approach to the κ-opioid antagonist aticaprant.

Total Synthesis of the Tetracyclic Pyridinium Alkaloid epi-Tetradehydrohalicyclamine B

The first total synthesis of a tetracyclic marine pyridinium alkaloid hinged on recent advances in chemoselectivity management: While many classical methods failed to afford the perceptively simple pyridine-containing core of the target, nickel/iridium photoredox dual catalysis allowed the critical C-C bond to be formed in good yield. Likewise, ring closing alkyne metathesis (RCAM) worked well in the presence of the unhindered pyridine despite the innately Lewis acidic Mo(+6) center of the alkylidyne catalyst. Finally, an iridium catalyzed hydrosilylation was uniquely effective in reducing a tertiary amide without compromising an adjacent pyridine and the lateral double bonds; this transformation is largely without precedent. The second strained macrocycle enveloping the core was closed by intramolecular N-alkylation with formation of the pyridinium unit; the reaction proceeded site- and chemoselectively in the presence of an a priori more basic tertiary amine.

Unified synthesis of multiply arylated alkanes by catalytic deoxygenative transformation of diarylketones

A deoxygenative transformation of diarylketones leading to multiply arylated alkanes was developed. Diarylketones were reacted with diphenylphosphine oxide resulting in a phospha-Brook rearrangement, followed by palladium-catalyzed cross-couplings or a Friedel-Crafts type alkylation to afford the corresponding multiply arylated alkanes. A variety of diarylketones can be converted to multiply arylated alkanes such as diarylmethanes, tetraarylethanes, and triarylmethanes by reduction, dimerization, and arylation in one pot. Furthermore, a one-pot conversion from arylcarboxylic acids to diarylmethanes and tetraarylethanes, and a synthesis of tetraarylmethane and triphenylethane using sequential coupling reactions are also presented.

Total Syntheses of Calyciphylline A-Type Alkaloids (-)-10-Deoxydaphnipaxianine A, (+)-Daphlongamine E and (+)-Calyciphylline R via Late-Stage Divinyl Carbinol Rearrangements

Among the famous Daphniphyllum alkaloids family, the calyciphylline A-type subfamily has triggered particular interest from the organic synthesis community in recent years. Here, we report divergent total syntheses of three calyciphylline A-type alkaloids, namely, (-)-10-deoxydaphnipaxianine A, (+)-daphlongamine E, and (+)-calyciphylline R. Our work highlights an efficient, divergent strategy via late-stage divinyl carbinol rearrangements, including an unprecedented oxidative Nazarov electrocyclization using an unfunctionalized tertiary divinyl carbinol and an unusual allylic alcohol rearrangement. A highly efficient "donor-acceptor" platinum catalyst was used for a critical nitrile hydration step. Moreover, the power of selective amide reductions has also been showcased by novel and classic tactics.

Ir-Catalyzed Chemoselective Reductive Condensation Reactions of Tertiary Amides with Active Methylene Compounds

The catalytic reductive condensation reactions of tertiary amides with active methylene compounds leading to multifunctionalized non-N-containing products is described. The reactions proceed through sequential iridium-catalyzed hydrosilylation of the amides followed by acid-mediated condensation with the active methylene compounds. This scalable method is broad in scope and shows remarkable chemoselectivity for the amide group in the presence of several sensitive or even more reactive functionalities such as ester, cyano, nitro, silyl dienol ether, and ketone.

Recent advances in visible light-induced C(sp3)–N bond formation

Synthetic chemists have long focused on selective C(sp ³)-N bond-forming approaches in response to the high value of this motif in natural products, pharmaceutical agents and functional materials. In recent years, visible light-induced protocols have become an important synthetic platform to promote this transformation under mild reaction conditions. These photo-driven methods rely on converting visible light into chemical energy to generate reactive but controllable radical species. This Review highlights recent advances in this area, mostly after 2014, with an emphasis placed on C(sp ³)-H bond activations, including amination of olefins and carbonyl compounds, and cross-coupling reactions.

Asymmetric Synthesis of Propargylic α-Stereogenic Tertiary Amines by Reductive Alkynylation of Tertiary Amides Using Ir/Cu Tandem Catalysis

The development of an asymmetric protocol for the reductive alkynylation of amides to access important α-stereogenic tertiary propargylic amines is reported using a tandem Ir-catalyzed hydrosilylation/enantioselective Cu-catalyzed alkynylation. The reaction utilizes a Cu/PyBox catalyst system in the alkynylation step to achieve asymmetry and affords excellent yields with moderate to good levels of enantiocontrol while employing low Ir-catalyst loadings (0.5 mol %).

KOtBu-Mediated Reductive Cyanation of Tertiary Amides for Synthesis of α-Aminonitriles

A simple, mild, catalyst-free, and efficacious KO^tBu-mediated reductive cyanation reaction of tertiary amides under hydrosilylation conditions has been described. A series of α-aminonitriles is obtained in moderate to high yield with good functional group tolerance. The reaction works well with a readily available amide substrate, a cheap and versatile base KO^tBu, and a commercially available hydrosilane (EtO)₃SiH and is convenient for workup and purification.

Combined experimental and computational study of Al2O3 catalyzed transamidation of secondary amides with amines

Amides are the most extensively used substances in both synthetic organic and bioorganic chemistry. Unfortunately, the traditional synthesis of amides suffers from some important drawbacks, including low atom efficiency, high catalyst loading, separation of products from the reaction mixture and production of byproducts. Al2O3 is an amphoteric catalyst that activates the carbonyl carbon of the secondary amide group and helps the C-N cleavage of the reactant amide group by attacking the N-H hydrogen. By using the concepts of amphoteric properties of Al2O3, amides were synthesized from secondary amides and amines in the presence of triethylamine solvent. Several aliphatic and aromatic amines were used for the transamidation of N-methylbenzamide in the presence of the Al2O3 catalyst. Moreover, using the Gaussian09 software at the DFT level, HUMO, LUMO and the intrinsic reaction coordinates (IRCs) have also been calculated to find out the transition state of the reaction and energy. In this study, five successful compounds were synthesized by the transamidation of secondary amides with amines using a reusable Al2O3 catalyst. The catalyst was reused several times with no significant loss in its catalytic activity. The products were purified by recrystallization and column chromatography techniques. This catalytic method is effective for the simultaneous activation of the carbonyl group and N-H bond by using the Al2O3 catalyst.