Iridium-catalysed reductive allylic amination of α,β-unsaturated aldehydes

Allylic amination is a powerful tool for constructing N-allylic amines widely found in bioactive molecules. Generally, allylic alcohols and unsaturated hydrocarbons have been considered for allylic amination reactions to minimize waste production. Herein, we present an iridium-catalysed method for reductive allylic amination of α,β-unsaturated aldehydes with amines to afford N-allylic amines under air conditions. This protocol is demonstrated to provide products from many substrates (41 examples) in moderate-to-excellent yields. This synthetic methodology is also highlighted by the synthesis of drug molecules, optically pure products, as well as scale-up experiments.

Merging of Light/Dark Palladium Catalytic Cycles Enables Multicomponent Tandem Alkyl Heck/Tsuji-Trost Homologative Amination Reaction toward Allylic Amines

A visible light-induced palladium-catalyzed homologative three-component synthesis of allylic amines has been developed. This protocol proceeds via a unique mechanism involving two distinct cycles enabled by the same Pd(0) catalyst: a visible light-induced hybrid radical alkyl Heck reaction between 1,1-dielectrophile and styrene, followed by the "in dark" classical Tsuji-Trost-type allylic substitution reaction. This method works well with a broad range of primary and secondary amines, aryl alkenes, dielectrophiles, and in complex settings. The regiochemistry of the obtained products is primarily governed by the structure of 1,1-dielectrophile. Involvement of π-allyl palladium intermediates allowed for the control of stereoselectivity, which has been demonstrated with up to 95:5 er.

Supported Ionic Liquid Phase (SILP) Allylic Alkylation of Amines in Continuous Flow

We present the use of Pd-complex-containing supported ionic liquid phases (SILPs) as a novel approach for continuous-flow allylic alkylation of N-nucleophiles. This immobilization strategy gave simple access to air-tolerating catalyst frameworks, providing rapid and convenient access to various achiral and chiral N-allylation products. Under optimized conditions, the flow-reaction could be maintained for 3.5 hours with constant product output; meanwhile, only a marginal 0.7 wt % of ionic liquid leaching and no detectable palladium-complex leaching could be observed.

Palladium-Catalyzed Oxidative Amination of Unactivated Olefins with Primary Aliphatic Amines

Direct coupling of unactivated olefins with primary alkylamines is considered to be an efficient but unknown method for the construction of complex amines. Herein we report a catalytic intermolecular oxidative amination of unactivated olefins with primary aliphatic amines based on the combination of a palladium catalyst, a bidentate phosphine ligand, and duroquinone. A range of secondary allylic amines were obtained in good yields with excellent regio- and stereoselectivity. Mechanistic control experiments revealed that the reaction proceeds by allylic C(sp³)-H activation and nucleophilic amination. The utility of the protocol is further demonstrated with the late-stage modification and streamlined synthesis of drug molecules.

A unified approach to benzo[c]phenanthridines via the cascade dual-annulation/formylation of 2-alkynyl/alkenylbenzonitriles

A base-mediated versatile cascade dual-annulation and formylation of 2-alkenyl/alkynylbenzonitriles with 2-methylbenzonitriles has been established for the construction of four different classes of amino and amido substituted benzo[c]phenanthridines and benzo[c]phenanthrolines. The synthesized molecules could be of utmost relevance in pharmaceuticals. The transformation uses the solvent DMF as the formyl source for synthesis of the amido-substituted scaffolds. This transition-metal-free unique strategy enables the formation of multiple C-C and C-N bonds in one pot at room temperature.

Synergistic improvement of cinnamylamine production by metabolic regulation

BACKGROUND

Aromatic primary amines (APAs) are key intermediates in the chemical industry with numerous applications. Efficient and mild biocatalytic synthesis is an excellent complement to traditional chemical synthesis. Our lab previously reported a whole-cell catalytic system for the synthesis of APAs catalyzed by carboxylic acid reductase from Neurospora crassa (ncCAR) and ω-transaminase from Ochrobactrum anthropi (OATA). However, the accumulation of toxic intermediates (aromatic aldehydes) during biocatalytic synthesis affected yields of APAs due to metabolic imbalance.

RESULTS

In this work, the biocatalytic synthesis of APAs (taking cinnamylamine as an example) was metabolically regulated by the overexpression or knockout of five native global transcription factors (TFs), the overexpression of eight native resistance genes, and optimization of promoters. Transcriptome analysis showed that knockout of the TF arcA increased the fluxes of NADPH and ATP in E. coli, while the rate of pyruvate metabolism was accelerated. In addition, the genes related to stress and detoxification were upregulated with the overexpression of resistance gene marA, which reduced the NADPH level in E. coli. Then, the expression level of soluble OATA increased by promoter optimization. Overall, arcA and marA could regulate the catalytic rate of NADPH- dependent ncCAR, while arcA and optimized promoter could regulate the catalytic rate of OATA. Lastly, the cinnamylamine yield of the best metabolically engineered strain S020 was increased to 90% (9 mM, 1.2 g/L), and the accumulation of cinnamaldehyde was below 0.9 mM. This work reported the highest production of cinnamylamine by biocatalytic synthesis.

CONCLUSION

This regulatory process provides a common strategy for regulating the biocatalytic synthesis of other APAs. Being entirely biocatalytic, our one-pot procedure provides considerable advantages in terms of environmental and safety impacts over reported chemical methods.

COAP/Pd-Catalyzed Linear Asymmetric Allylic Alkylation for Optically Active 3,3-Disubstituted Oxindole Derivatives with a Four-Carbon Amino Side Chain

An asymmetric linear selective allylic alkylation of vinylaziridines with 3-aryl oxindoles has been developed by using a chiral oxamide-phosphine (COAP-Bn-OMe-p)/palladium complex in methanol, which furnished a wide variety of 3,3-disubstituted oxindole derivatives in good yields with excellent regio- and enantioselectivities.

Dehydrative Cross-Coupling for C-N Bond Construction under Transition-Metal-Free Conditions

A transition-metal-free catalytic system was designed to address the dehydrative cross-coupling of unactivated primary/secondary alcohols with amines/amides under environmentally benign conditions. Mg²⁺ and counteranion (PF₆^-) worked synergistically to realize C-OH bond cleavage and concomitant C-N bond formation. A wide range of allylic alcohols and amines/amides were tolerated well in this transformation, which allowed C-N bond construction with high efficiency.

Enzymatic N-Allylation of Primary and Secondary Amines Using Renewable Cinnamic Acids Enabled by Bacterial Reductive Aminases

Allylic amines are a versatile class of synthetic precursors of many valuable nitrogen-containing organic compounds, including pharmaceuticals. Enzymatic allylic amination methods provide a sustainable route to these compounds but are often restricted to allylic primary amines. We report a biocatalytic system for the reductive N-allylation of primary and secondary amines, using biomass-derivable cinnamic acids. The two-step one-pot system comprises an initial carboxylate reduction step catalyzed by a carboxylic acid reductase to generate the corresponding α,β-unsaturated aldehyde in situ. This is followed by reductive amination of the aldehyde catalyzed by a bacterial reductive aminase pIR23 or BacRedAm to yield the corresponding allylic amine. We exploited pIR23, a prototype bacterial reductive aminase, self-sufficient in catalyzing formal reductive amination of α,β-unsaturated aldehydes with various amines, generating a broad range of secondary and tertiary amines accessed in up to 94% conversion under mild reaction conditions. Analysis of products isolated from preparative reactions demonstrated that only selective hydrogenation of the C=N bond had occurred, preserving the adjacent alkene moiety. This process represents an environmentally benign and sustainable approach for the synthesis of secondary and tertiary allylic amine frameworks, using renewable allylating reagents and avoiding harsh reaction conditions. The selectivity of the system ensures that bis-allylation of the alkylamines and (over)reduction of the alkene moiety are avoided.

Allylic C-H amination cross-coupling furnishes tertiary amines by electrophilic metal catalysis

Intermolecular cross-coupling of terminal olefins with secondary amines to form complex tertiary amines-a common motif in pharmaceuticals-remains a major challenge in chemical synthesis. Basic amine nucleophiles in nondirected, electrophilic metal-catalyzed aminations tend to bind to and thereby inhibit metal catalysts. We reasoned that an autoregulatory mechanism coupling the release of amine nucleophiles with catalyst turnover could enable functionalization without inhibiting metal-mediated heterolytic carbon-hydrogen cleavage. Here, we report a palladium(II)-catalyzed allylic carbon-hydrogen amination cross-coupling using this strategy, featuring 48 cyclic and acyclic secondary amines (10 pharmaceutically relevant cores) and 34 terminal olefins (bearing electrophilic functionality) to furnish 81 tertiary allylic amines, including 12 drug compounds and 10 complex drug derivatives, with excellent regio- and stereoselectivity (>20:1 linear:branched, >20:1 E:Z).

pH-Mediated Selective Synthesis of N-Allylic Alkylation or N-Alkylation Amines with Allylic Alcohols via an Iridium Catalyst in Water

Amination of allylic alcohols is an effective approach in the facile synthesis of N-allylic alkylation or N-alkylation amines. Recently, a series of catalysts were devised to push forward this transformation. However, current synthetic methods are typically limited to achieve either N-allylic alkylation or N-alkylation products via a certain catalyst. In this article, a pH-mediated selective synthesis of N-allylic alkylation or N-alkylation amines with allylic alcohols via an iridium catalyst with water as the environmental benign solvent is revealed, enabling the miscellaneous synthesis of N-allylic alkylation and N-alkylation products in outstanding yields. Furthermore, a gram-scale experiment with low catalyst loading offers the potential to access a distinct entry for the synthesis of the antifungal drug naftifine.

Boron-catalyzed dehydrative allylation of 1,3-diketones and β-ketone esters with 1,3-diarylallyl alcohols in water

A metal-free catalytic allylation with atom economy and green environment friendly was developed. Allylic alcohols could be directly dehydrated in water by B(C6F5)3, without using any base additives. The reaction can afford the corresponding monoallylated product in moderate to high yield and has been performed on a gram-scale, and a quaternary carbon center can be constructed for the active methine compounds of 1,3-diketones or β-ketone esters in this process. The product can be further converted, such as the synthesis of tetra-substituted pyrazole compounds, or 1,4-dienes and functionalized dihydropyrans.

Substrate-Controlled Cu(OAc)2-Catalyzed Stereoselective Semi-Reduction of Alkynes with MeOH as the Hydrogen Source

A substrate-controlled stereoselective semi-reduction of alkynes with MeOH as the hydrogen source has been developed, and readily available Cu(OAc)₂ (copper acetate) is utilized as an optimal catalyst. The detailed investigation of the mechanism revealed distinct catalytic processes for the (Z)- and (E)-alkenes, respectively. As a result, a diversity of alkynes (including terminal, internal alkynes etc.) were compatible under the mild reaction conditions. Furthermore, the high proportion of deuterium in Z-alkenes (up to 96%) was obtained using d ₄-methanol as a solvent.

K2CO3 Promoted Cascade Reaction for the Preparation of 1H-Imidazol-4- yl-1-amine Derivatives

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A K2CO3 promoted efficient one pot two-step method for the preparation of 1H-imidazol-4- yl-1-amine derivatives has been developed. A series of second amines with an imidazole group were obtained with 56%-91% yields by the K2CO3 promoted amination of acetates and nitrogen deprotection of the imidazole process.

Cobalt-Catalyzed Allylation of Amides with Styrenes Using DMSO as Both the Solvent and the α-Methylene Source

An efficient synthesis of privileged allylic amines has been developed via cobalt-catalyzed allylation of amides with styrenes, in which DMSO was used as both the solvent and the α-methylene source. This transformation features high yields, and selectivity for the (E)-isomer of the linear product. Through the experimental and computational investigations, a sequential K₂S₂O₈-mediated oxidative coupling/cobalt-assisted regioselective alkene insertion/β-H elimination/alkene dissociation/hydride transfer process has also been deduced.

Metal-Organic Capsules with NADH Mimics as Switchable Selectivity Regulators for Photocatalytic Transfer Hydrogenation

Switchable selective hydrogenation among the groups in multifunctional compounds is challenging because selective hydrogenation is of great interest in the synthesis of fine chemicals and pharmaceuticals as a result of the importance of key intermediates. Herein, we report a new approach to highly selectively (>99%) reducing C═X (X = O, N) over the thermodynamically more favorable nitro groups locating the substrate in a metal-organic capsule containing NADH active sites. Within the capsule, the NADH active sites reduce the double bonds via a typical 2e^- hydride transfer hydrogenation, and the formed excited-state NAD⁺ mimics oxidize the reductant via two consecutive 1e^- processes to regenerate the NADH active sites under illumination. Outside the capsule, nitro groups are highly selectively reduced through a typical 1e^- hydrogenation. By combining photoinduced 1e^- transfer regeneration outside the cage, both 1e^- and 2e^- hydrogenation can be switched controllably by varying the concentrations of the substrates and the redox potential of electron donors. This promising alternative approach, which could proceed under mild reaction conditions and use easy-to-handle hydrogen donors with enhanced high selectivity toward different groups, is based on the localization and differentiation of the 2e^- and 1e^- hydrogenation pathways inside and outside the capsules, provides a deep comprehension of photocatalytic microscopic reaction processes, and will allow the design and optimization of catalysts. We demonstrate the advantage of this method over typical hydrogenation that involves specific activation via well-modified catalytic sites and present results on the high, well-controlled, and switchable selectivity for the hydrogenation of a variety of substituted and bifunctional aldehydes, ketones, and imines.

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.

Substrate Self-Assisted Secondary Bond Activation of Allylic Alcohol in a Tsuji-Trost Reaction Revealed by NMR Methods

The first experimental evidence for the palladium-catalyzed secondary bond activation of allylic alcohols in a Tsuji-Trost reaction was provided by NMR methods, such as variable-temperature ¹H NMR, diffusion-ordered spectroscopy (DOSY), Job's method, ¹H NMR titration, and nuclear Overhauser enhancement spectroscopy (NOESY). The experimental results revealed that the substrate self-assisted activation of allylic alcohols is probably performed via a 1:1 binding six-membered-ring complex, which are formed by the formation of the secondary bonds, the hydrogen bond and P···O noncovalent bond between allylic alcohol and phosphonium ylide.

Photoredox-catalyzed branch-selective pyridylation of alkenes for the expedient synthesis of Triprolidine

Alkenylpyridines are important pharmaceutical cores as well as versatile building blocks in organic synthesis. Heck reaction represents one of the most powerful platform for the construction of aryl-substituted alkenes, nevertheless, examples for Heck type coupling of alkenes with pyridines, particularly with branched selectivity, remain elusive. Here we report a catalytic, branch-selective pyridylation of alkenes via a sulfinate assisted photoredox catalysis. This reaction proceeds through a sequential radical addition/coupling/elimination, by utilizing readily available sodium sulfinates as reusable radical precursors as well as traceless elimination groups. This versatile protocol allows for the installation of important vinylpyridines with complete branched selectivity under mild conditions. Furthermore, this catalytic manifold is successfully applied to the expedient synthesis of Triprolidine.

Alkenylpyridines are versatile building blocks for the synthesis of drugs and other complex molecular structures. Here, the authors show a branch-selective pyridylation of alkenes via sulfinate-assisted photoredox catalysis and showcase its utility in an expedient synthesis of Triprolidine.

Dehydrative Allylation between Aldehydes and Allylic Alcohols through Synergistic N-Heterocyclic Carbene/Palladium Catalysis

Dehydrative allylation between widely available aldehydes and allylic alcohols to afford β,γ-unsaturated ketones was enabled by a synergistic merger of a thiazolium N-heterocyclic carbene catalyst and a palladium-bisphosphine catalyst.

Domino Synthesis of α,β-Unsaturated γ-Lactams by Stereoselective Amination of α-Tertiary Allylic Alcohols

Tertiary allylic alcohols equipped with a carboxyl group can be smoothly aminated under ambient conditions by a conceptually new and stereoselective protocol under palladium catalysis. The in situ formed Z-configured γ-amino acid cyclizes to afford an α,β-unsaturated γ-lactam, releasing water as the only byproduct. This practical catalytic transformation highlights the use of a carboxyl group acting as an activating and stereodirecting functional group to provide a wide series of pharma-relevant building blocks. Various control reactions support the crucial role of the carboxyl group in the substrate to mediate these transformations.

C-N Bond Formation from Allylic Alcohols via Cooperative Nickel and Titanium Catalysis

Amination of allylic alcohols is facilitated via cooperative catalysis. Catalytic Ti(O- i-Pr)₄ is shown to dramatically increase the rate of nickel-catalyzed allylic amination, and mechanistic experiments confirm activation of the allylic alcohol by titanium. Aminations of primary and secondary allylic alcohols are demonstrated with a variety of amine nucleophiles. Diene-containing substrates also cyclize onto the nickel allyl intermediate prior to amination, generating carbocyclic amine products. This tandem process is only achieved under our cooperative catalytic system.

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

The preparation of allylic amines is traditionally accomplished by reactions of amines with reactive electrophiles, such as allylic halides, sulfonates, or oxyphosphonium species; such methods involve hazardous reagents, generate stoichiometric waste streams, and often suffer from side reactions (such as overalkylation). We report here the first broad-scope nickel-catalysed direct amination of allyl alcohols: An inexpensive Ni^II /Zn couple enables the allylation of primary, secondary, and electron-deficient amines without the need for glove-box techniques. Under mild conditions, primary and secondary aliphatic amines react smoothly with a range of allyl alcohols, giving secondary and tertiary amines efficiently. This "totally catalytic" method can also be applied to electron-deficient nitrogen nucleophiles; the practicality of the process was demonstrated in an efficient, gram-scale preparation of the calcium antagonist drug substance flunarizine (Sibelium®).

Catalytic C-N and C-H Bond Activation: ortho-Allylation of Benzoic Acids with Allyl Amines

A facile insertion of ruthenium into aromatic C-H and allylic C-N bonds are the key steps in a [Ru( p-cymene)Cl₂]₂-catalyzed ortho-C-H allylation of benzoic acids. This protocol allows drawing on the large pool of allylic amines for state-of-the-art ortho-functionalizations of arenes, turning neutral amines into leaving groups. Concise syntheses of biologically active compounds provide further evidence of the synthetic potential of this methodology.

Rhodium-catalyzed asymmetric hydroamination and hydroindolation of keto-vinylidenecyclopropanes

We reported a highly regio- and enantioselective hydroamination and hydroindolation of keto-vinylidenecyclopropanes via cationic Rh(i) catalysis in this context. The combination of various secondary amines and indoles with keto-vinylidenecyclopropanes afforded the corresponding hydrofunctionalization products in good to excellent yields with outstanding ee values under mild conditions. A new TMM-Rh model complex was proposed, providing an atom economical Rh-π-allyl precursor at the same time. Moreover, the resulting products could easily be transformed into more complex polyheterocycles upon further synthetic manipulation.

Postsynthetic modification of single Pd sites into uncoordinated polypyridine groups of a MOF as the highly efficient catalyst for Heck and Suzuki reactions

A novel Pd-HoMOF catalyst was prepared, which displayed good thermal stability and high activity in Heck and Suzuki cross-coupling reactions.

Pd/Cu dual catalysis: highly enantioselective access to α-substituted α-amino acids and α-amino amides

In this work, we have developed a synergistic Pd/Cu catalyst system for the asymmetric allylation of glycine iminoesters/amides, affording a range of α-substituted α-amino acids/amides in high yields and with excellent enantioselectivities (88 → 99% ee).

Aqueous protocol for allylic arylation of cinnamyl acetates with sodium tetraphenylborate using a Bedford-type palladacycle catalyst

Allylic arylation using 0.002 mol% of a Bedford-type palladacycle catalyst is described under mild reaction conditions.