One-Pot N-Deprotection and Catalytic Intramolecular Asymmetric Reductive Amination for the Synthesis of Tetrahydroisoquinolines

Direct synthesis of chiral β-arylamines via additive-free asymmetric reductive amination enabled by tunable bulky phosphoramidite ligands

This report describes an additive-free iridium-catalyzed direct asymmetric reductive amination that enables the efficient synthesis of chiral β-arylamines, which are important pharmacophores present in a wide variety of pharmaceutical drugs. The reaction makes use of bulky and tunable phosphoramidite ligands for high levels of enantiomeric control, even for alkylamino coupling partners which lack secondary coordinating sites. The synthetic value of this succinct procedure is demonstrated by single-step synthesis of multiple drugs, analogs and key intermediates. Mechanistic investigations reveal an enamine-reduction pathway, in which H-bonding, steric repulsion, and CH-π and electrostatic interactions play important roles in defining the spatial environment for the "outer-sphere" hydride addition.

Spiro-Josiphos Ligands for the Ir-Catalyzed Asymmetric Synthesis of Chiral Amines under Hydrogenation Conditions

Transition metal-catalyzed asymmetric hydrogenation possesses unparalleled advantages to prepare chiral amines. Here we reported a novel ligand that combined Josiphos and a spirobiindane scaffold and simultaneously investigated its application in Ir-catalyzed asymmetric hydrogenation for the synthesis of chiral amines. Excellent catalytic activity (5000 TON), high enantioselectivity (up to 99% ee), and broad substrate scope (different C═N substrates) make it highly promising for both academic research and industrial applications.

Novel Sulfonamide Derivatives Containing a Piperidine Moiety as New Bactericide Leads for Managing Plant Bacterial Diseases

Plant bacterial diseases are an intractable problem due to the fact that phytopathogens have acquired strong resistances for traditional pesticides, resulting in restricting the quality and yield of agricultural products around the world. To develop new agrochemical alternatives, we prepared a novel series of sulfanilamide derivatives containing piperidine fragments and assessed their antibacterial potency. The bioassay results revealed that most molecules displayed excellent in vitro antibacterial potency towards Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas axonopodis pv. citri (Xac). In particular, molecule C₄ exhibited outstanding inhibitory activity toward Xoo with EC₅₀ value of 2.02 µg mL^-1, which was significantly better than those of the commercial agents bismerthiazol (EC₅₀ = 42.38 µg mL^-1) and thiodiazole copper (EC₅₀ = 64.50 µg mL^-1). A series of biochemical assays confirmed that compound C₄ interacted with dihydropteroate synthase, and irreversibly damaged the cell membrane. In vivo assays showed that the molecule C₄ presented acceptable curative and protection activities of 34.78% and 39.83%, respectively, at 200 µg mL^-1, which were greater than those of thiodiazole and bismerthiazol. This study highlights the valuable insights for the excavation and development of new bactericides that can concurrently target dihydropteroate synthase and bacterial cell membranes.

1,2-Diamines as the Amine Sources in Amidation and Rhodium-Catalyzed Asymmetric Reductive Amination Cascade Reactions

The sturdy chelation of 1,2-diamines and transition-metals would retard or even interrupt the routine catalytic cycles. In the amidation and asymmetric reductive amination (ARA) cascade reactions of diamines and ketoesters, we deployed sets of additives to ensure a smooth transformation catalyzed by the complexes of rhodium and versatile and highly modular phosphoramidite-phosphine ligands. The tunability of the ligands was fully exploited to accommodate various diamines and α-ketoesters for the efficient synthesis of chiral 3,4-dihydroquinoxalinones.

Iridium-catalyzed direct asymmetric reductive amination utilizing primary alkyl amines as the N-sources

Direct asymmetric reductive amination is one of the most efficient methods for the construction of chiral amines, in which the scope of the applicable amine coupling partners remains a significant challenge. In this study we describe primary alkyl amines effectively serve as the N-sources in direct asymmetric reductive amination catalyzed by the iridium precursor and sterically tunable chiral phosphoramidite ligands. The density functional theory studies of the reaction mechanism imply the alkyl amine substrates serve as a ligand of iridium strengthened by a (N)H-O(P) hydrogen-bonding attraction, and the hydride addition occurs via an outer-sphere transition state, in which the Cl-H H-bonding plays an important role. Through this concise procedure, cinacalcet, tecalcet, fendiline and many other related chiral amines have been synthesized in one single step with high yields and excellent enantioselectivity.

Direct asymmetric reductive amination is one of the most efficient methods for obtaining chiral amines. Here the authors show how primary alkyl amines can undergo this transformation in the presence of an iridium catalyst with sterically tuneable chiral phosphoramidite ligands, achieving the synthesis of pharmaceutical compounds.

Recent Advances in the Enantioselective Synthesis of Chiral Amines via Transition Metal-Catalyzed Asymmetric Hydrogenation

Chiral amines are key structural motifs present in a wide variety of natural products, drugs, and other biologically active compounds. During the past decade, significant advances have been made with respect to the enantioselective synthesis of chiral amines, many of them based on catalytic asymmetric hydrogenation (AH). The present review covers the use of AH in the synthesis of chiral amines bearing a stereogenic center either in the α, β, or γ position with respect to the nitrogen atom, reported from 2010 to 2020. Therefore, we provide an overview of the recent advances in the AH of imines, enamides, enamines, allyl amines, and N-heteroaromatic compounds.

Direct asymmetric reductive amination of α-keto acetals: a platform for synthesizing diverse α-functionalized amines

We report an efficient and straightforward method to synthesize enantio-enriched N-unprotected α-amino acetals via ruthenium-catalyzed direct asymmetric reductive amination. The α-amino acetal products are versatile and valuable platform molecules that can be converted to the corresponding α-amino acids, amino alcohols, and other derivatives by convenient transformations.

Iridium-Catalyzed Asymmetric Cascade Allylation/Pictet-Spengler Cyclization Reaction for the Enantioselective Synthesis of 1,3,4-Trisubstituted Tetrahydroisoquinolines

An iridium-catalyzed trifluoroacetic acid-promoted asymmetric cascade allylation/Pictet-Spengler cyclization reaction of azomethine ylides with aromatic allylic alcohols is reported. This protocol provides a facile and scalable method for the construction of 1,3,4-trisubstituted tetrahydroisoquinolines containing two stereogenic centers in good yields (up to 96%) with generally excellent diastereo- and enantioselectivities (up to >20:1 dr and >99% ee). Furthermore, a series of aromatic heterocycle-fused piperidines were also obtained with excellent enantiocontrol by this methodology.

Enantioselective Synthesis of 1-Aryl Tetrahydroisoquinolines by the Rhodium-Catalyzed Reaction of 3,4-Dihydroisoquinolinium Tetraarylborates

The 1-aryl tetrahydroisoquinolines (1-aryl THIQs) are omnipresent in biologically active molecules. Here we report on the direct asymmetric synthesis of these valuable compounds via the reaction of 3,4-dihydroisoquinolinium tetraarylborates. The dual roles of anionic tetraarylborates, which function as both prenucleophiles and stabilizers of 3,4-dihydroisoquinolinium cations, enable this rhodium(I)-catalyzed protocol to convergently provide enantioenriched 1-aryl THIQs in good yields (≤95%) with ≤97% ee, as demonstrated by the formal synthesis of (-)-solifenacin and the facile synthesis of (-)-Cryptostyline I.

Enantioselective synthesis of tetrahydroisoquinolines via catalytic intramolecular asymmetric reductive amination

A highly efficient intramolecular asymmetric reductive amination transformation catalyzed by an iridium complex of ^tBu-ax-Josiphos has been realized, providing an efficient access to various THIQ alkaloids.

Recent advances on transition-metal-catalysed asymmetric reductive amination

This review focuses on the recent progress of homogeneous transition-metal-catalysed asymmetric reductive amination of ketones with diverse nitrogen sources.

Iridium-Catalyzed Asymmetric Hydrogenation of Sterically Hindered Cyclic Imines for Enantioselective Synthesis of Tetrahydroisoquinolines

An efficient enantioselective hydrogenation of sterically hindered cyclic imines catalyzed by the Ir-^tBu-ax-Josiphos complex has been described, producing a series of useful chiral bulky tetrahydroisoquinoline analogs in high isolated yields (85-96%) with good to excellent enantioselectivities (74-99% ee). This transformation provided highly straightforward access to the useful derivatives of tetrahydroisoquinolines, which are of great potential value in drug molecule and natural product research.

Asymmetric Reductive Amination/Ring-Closing Cascade: Direct Synthesis of Enantioenriched Biaryl-Bridged NH Lactams

We report here a Ru-catalyzed enantioselective synthesis of biaryl-bridged NH lactams through asymmetric reductive amination and a spontaneous ring-closing cascade from keto esters and NH₄OAc with H₂ as reductant. The reaction features broad substrate generality and high enantioselectivities (up to >99% ee). To showcase the practical utility, a highly enantioselective synthesis of 5-ethylindolobenzazepinone C, a promising antimitotic agent, has been rapidly completed. Furthermore, the amide group in the products enables versatile elaborations through directed C-H functionalization.

The combination of asymmetric hydrogenation of olefins and direct reductive amination

Asymmetric hydrogenation (AH) and direct reductive amination (DRA) are both efficient transformations frequently utilized in industry. Here we combine the asymmetric hydrogenation of prochiral olefins and direct reductive amination of aldehydes in one step using hydrogen gas as the common reductant and a rhodium-Segphos complex as the catalyst. With this strategy, the efficiency for the synthesis of the corresponding chiral amino compounds is significantly improved. The practical application of this synthetic approach is demonstrated by the facile synthesis of chiral 3-phenyltetrahydroquinoline and 3-benzylindoline compounds.

Iridium-catalyzed enantioselective reductive amination of aromatic ketones

A highly efficient catalytic system of direct asymmetric reductive amination of aromatic ketones.

A diversity of recently reported methodology for asymmetric imine reduction

This review describes recent developments in enantioselective imine reduction, including related substrates in which a CN bond is the target for reduction, and in situ methods.

Secondary amines as coupling partners in direct catalytic asymmetric reductive amination

The secondary amine participating asymmetric reductive amination remains an unsolved problem in organic synthesis. Here we show for the first time that secondary amines are capable of effectively serving as N-sources in direct asymmetric reductive amination to afford corresponding tertiary chiral amines with the help of a selected additive set under mild conditions (0-25 °C). The applied chiral phosphoramidite ligands are readily prepared from BINOL and easily modified. Compared with common tertiary chiral amine synthetic methods, this procedure is much more concise and scalable, as exemplified by the facile synthesis of rivastigmine and N-methyl-1-phenylethanamine.

Intramolecular asymmetric reductive amination: synthesis of enantioenriched dibenz[c,e]azepines

An enantioselective synthesis of dibenz[c,e]azepines containing both central and axial chiralities through a one pot N-Boc deprotection/intramolecular asymmetric reductive amination sequence has been achieved with generally excellent enantiocontrol (up to 97% ee).

An Ir-catalyzed intramolecular asymmetric reductive amination (ARA) of bridged biaryl derivatives has been described. Using this unprecedented approach, synthetically useful dibenz[c,e]azepines containing both central and axial chiralities are obtained with excellent enantiocontrol (up to 97% ee). This methodology represents a rare example of enantioselective chemocatalytic synthesis of chiral dibenz[c,e]azepines featuring a broad substrate scope, and their synthetic utilities are exhibited by derivatizing the products into a chiral amino acid derivative and chiral phosphoramidite ligands, which display excellent enantiocontrol in Rh-catalyzed asymmetric hydrogenation of α-dehydroamino acid derivatives. Remarkably, our method is also applicable to enantioselectively synthesize an allocolchicine analogue.

Modular One-Step Three-Component Synthesis of Tetrahydroisoquinolines Using a Catellani Strategy

Reported is a modular one-step three-component synthesis of tetrahydroisoquinolines using a Catellani strategy. This process exploits aziridines as the alkylating reagents, through palladium/norbornene cooperative catalysis, to enable a Catellani/Heck/aza-Michael addition cascade. This mild, chemoselective, and scalable protocol has broad substrate scope (43 examples, up to 90 % yield). The most striking feature of this protocol is the excellent regioselectivity and diastereoselectivity observed for 2-alkyl- and 2-aryl-substituted aziridines to access 1,3-cis-substituted and 1,4-cis-substituted tetrahydroisoquinolines, respectively. Moreover, this is a versatile process with high step and atom economy.

Approach to Chiral 1-Substituted Isoquinolone and 3-Substituted Isoindolin-1-one by Addition-Cyclization Process

An approach to access 1-substituted isoquinolones has been developed through the addition-cyclization of imines with Grignard reagents in the presence of 2,2'-dipyridyl. A number of substituted aromatic magnesium reagents were amenable to this process, and the desired products were obtained with excellent yields and outstanding diastereoselectivities ( dr > 99:1). The utility of this convenient approach is demonstrated by the formal synthesis of ( S)-cryptostyline II. Moreover, N-methylmorpholine (NMM) was found to be an effective additive for the formation of 3-substituted isoindolin-1-ones using one-pot addition-cyclization-deprotection of imine with Grignard reagents.

A one-pot process for the enantioselective synthesis of tetrahydroquinolines and tetrahydroisoquinolines via asymmetric reductive amination (ARA)

Asymmetric reductive amination for the synthesis of both chiral tetrahydroquinolines and tetrahydroisoquinolines has been realized with an Ir/ZhaoPhos catalytic system via a one-pot N-Boc deprotection/intramolecular asymmetric reductive amination (ARA) sequence.

Facile synthesis of chiral indolines through asymmetric hydrogenation of in situ generated indoles

A concise synthesis of chiral indolines has been developed through intramolecular condensation, deprotection and palladium-catalyzed asymmetric hydrogenation in a one-pot process with up to 96% ee. A strong Brønsted acid played an important role in both the formation of indoles and asymmetric hydrogenation process.

An expedient and novel strategy for reductive amination by employing H2O as both a hydrogen source and solventviaB2(OH)4/H2O systems

An efficient, convenient and mild Ru-catalyzed reductive amination reaction was developed by employing H₂O as both hydrogen source and solventviaB₂(OH)₄/H₂O systems. α-Deuterated amines were also obtained expediently by employing D₂O in our catalytic systems.