Enantioselective Route Research Articles

Phenolic Dienes as Highly Selective Dienophiles in the Asymmetric Organocatalyzed Three-Component Vinylogous Povarov Reaction.

Our study presents a novel enantioselective route for the synthesis of 1,2,3,4-tetrahydroquinolines via a chiral phosphoric acid-catalyzed three-component Povarov reaction, employing phenolic dienes as dienophiles. This approach produces a diverse array of 2,3,4-trisubstituted tetrahydroquinolines, each featuring a styryl group at position 4, in high yields with excellent regio-, diastereo-, and enantioselectivities (>95:5 dr and up to >99% ee).

Asymmetric Synthesis of CIDD-0072424 via an Enantioselective Nitro-Mannich Reaction: A Central Nervous System Penetrant, Selective Small Molecule Inhibitor of Protein Kinase C Epsilon.

CIDD-0072424 is a novel small molecule developed in silico with remarkable activity for the inhibition of protein kinase C (PKC)-epsilon to treat alcohol use disorder. We developed a concise synthesis of (S)-2 that is highly enantioselective, scalable, and amenable for 3-point structure-activity relationship (SAR) studies for compound optimization. The highly enantioselective nitro-Mannich reaction was achieved through a dual-reagent catalysis system. The overall utility and the efficiency of the enantioselective route provided a scalable synthesis of both PKCε inhibitors 1 and 2.

Enantioselective route to an AE-ring intermediate in the total synthesis of talatisamine

Talatisamine [(–)-1] is a C19-diterpenoid alkaloid with an intricately fused ABCDEF-ring system. In 2020, we reported a total synthesis of racemic talatisamine [(±)-1], in which AE-ring fragment (±)-5-α/5-β was utilized as the pivotal early-stage intermediate. Herein, we disclose the development of an enantioselective route to (–)-5-β for the total synthesis of (–)-1. Enantioselective intermolecular Mannich, Lewis acid-mediated intramolecular Mannich, and reductive N-ethylation reactions were employed as the three key transformations.

Observation of Asymmetric Oxidation Catalysis with B20 Chiral Crystals**

AbstractThe study of heterogeneous reactions for enantiomeric processes based on inorganic crystals has been resurgent in recent years. However, the question remains how homochirality develops in nature and chemical reactions. Here, the successful growth of B20 group PdGa single crystals with different chiral lattices enabled us to achieve enantioselective recognition of 3,4‐dihydroxyphenylalanine (DOPA) based on a new mechanism, namely orbital angular momentum (OAM) polarization. The orbital textures of PdGa crystals indicate large OAM polarization near the Fermi level and carrying opposite signs. A positive or negative magnetization in the [111] direction is expected depending on the chiral lattice of PdGa crystals. Due to this, the adsorption energies of PdGa crystals and DOPA molecules differ depending on how well the O‐2p orbital of DOPA pairs with the Pd‐4d orbital of PdGa. The results provide one possible explanation for how chirality arises in nature by providing an enantioselective route with pure inorganic crystals.

Observation of Asymmetric Oxidation Catalysis with B20 Chiral Crystals.

The study of heterogeneous reactions for enantiomeric processes based on inorganic crystals has been resurgent in recent years. However, the question remains how homochirality develops in nature and chemical reactions. Here, the successful growth of B20 group PdGa single crystals with different chiral lattices enabled us to achieve enantioselective recognition of 3,4-dihydroxyphenylalanine (DOPA) based on a new mechanism, namely orbital angular momentum (OAM) polarization. The orbital textures of PdGa crystals indicate large OAM polarization near the Fermi level and carrying opposite signs. A positive or negative magnetization in the [111] direction is expected depending on the chiral lattice of PdGa crystals. Due to this, the adsorption energies of PdGa crystals and DOPA molecules differ depending on how well the O-2p orbital of DOPA pairs with the Pd-4d orbital of PdGa. The results provide one possible explanation for how chirality arises in nature by providing an enantioselective route with pure inorganic crystals.

Studies Towards The Synthesis of Tartrolons D and E

AbstractA concise and stereoselective synthesis of a key fragment C3-C22 unit of tartrolons D and E is demonstrated. Three crucial fragments are combined to form the 20-carbon chain, which contains four stereogenic centers in the monomeric unit of both natural products. The crucial fragments were synthesized in highly enantioselective routes from commercial starting compounds in two, eight, and two steps, respectively, and coupled using palladium-catalyzed Sonogashira coupling and directed 1,5-asymmetric aldol reaction as key steps.

Enantioselective Total Synthesis of (+)-KB343.

A concise total synthesis of the complex guanidinium toxin KB343 is reported traversing through an unusual sequence of chemoselective transformations and strategic skeletal reorganization. The absolute configuration is confirmed through an enantioselective route, and the structures of all key intermediates and the natural product itself are unassailably confirmed through X-ray crystallographic analysis.

Short, Divergent, and Enantioselective Total Synthesis of Bioactive ent-Pimaranes.

We present the first total synthesis of eight ent-pimaranes via a short and enantioselective route (11-16 steps). Key features of the divergent synthesis are a Sharpless asymmetric dihydroxylation, a Brønsted acid catalyzed cationic bicyclization, and a mild Rh-catalyzed arene hydrogenation for rapid access to a late synthetic branching point. From there on, selective functional group manipulations enable the synthesis of ent-pimaranes bearing different modifications in the A- and C-rings.

Enantioselective Nickel-Catalyzed Electrochemical Radical Allylation.

A simplified and appealing strategy via a chiral catalyst to facilitate the electrochemical process and provide asymmetric induction of radical reactions is particularly desirable and would have potential applications in electrosynthesis, organic chemistry, and drug discovery. Here, we introduced a novel electrolytic system that diverts the standard ionic reactivity to new catalytic functions, enabling mechanistically distinct single-electron transfer-based enantioselective routes to exhibit a brand-new pattern of reactivity-electricity-driven asymmetric catalysis as a privileged chiral platform for enantioselective radical allylation. The nickel-catalyzed activation of nucleophiles triggered a single-electron transfer process to provide a chiral catalyst-bound radical cation intermediate, which could be applied as an alternative strategy for the development of stereocontrolled radical reactions.

Enantioselective Nickel‐Catalyzed Electrochemical Radical Allylation

AbstractA simplified and appealing strategy via a chiral catalyst to facilitate the electrochemical process and provide asymmetric induction of radical reactions is particularly desirable and would have potential applications in electrosynthesis, organic chemistry, and drug discovery. Here, we introduced a novel electrolytic system that diverts the standard ionic reactivity to new catalytic functions, enabling mechanistically distinct single‐electron transfer‐based enantioselective routes to exhibit a brand‐new pattern of reactivity—electricity‐driven asymmetric catalysis as a privileged chiral platform for enantioselective radical allylation. The nickel‐catalyzed activation of nucleophiles triggered a single‐electron transfer process to provide a chiral catalyst‐bound radical cation intermediate, which could be applied as an alternative strategy for the development of stereocontrolled radical reactions.

Light‐Mediated Aminocatalysis: The Dual‐Catalytic Ability Enabling New Enantioselective Route

AbstractOver the last few decades, primary and secondary amines have been enormously used to trigger numerous valuable transformations. Likewise, modern‐day chemistry has witnessed the potentiality of visible‐light photoredox catalysis via single photoelectron transfer reactions. Recently, their synergistic effect has proved to be a crucial synthetic pillar, as several elegant protocols have their accessibility only under the cooperative action of this dual catalytic system. This catalytic system showcases a new green and sustainable synthetic approach which is advantageous from other methods. The emerging area of research demonstrates high efficiency of this dual‐catalytic system to access the plethora of molecular complexity enantioselectively. This Review comprises several momentous developments that surfaced in the last five years in the field of photoredox‐amine dual catalysis underpinning all types of synthetic transformations. By adapting the scope of each strategy, this Review will assist and inspire further development in this thriving field.

Palladium Catalysis Featuring Attractive Noncovalent Interactions Enabled Highly Enantioselective Access to β-Quaternary δ-Lactams

Described herein is a highly enantioselective route to β-quaternary δ-lactams by palladium/pyridine-dihydroisoquinoline (PyDHIQ)-catalyzed conjugate arylations. Notably, the effect of π-interactions on the high enantioselectivity was elucidated by DFT calculations and noncovalent interaction (NCI) analysis. The skeleton of the PyDHIQ ligand plays a key role in the formation of attractive noncovalent interactions with substrates in an enantioselectivity-determining step. The developed methodology was successfully applied to the asymmetric formal synthesis of (−)-picenadol.

Enantioselective synthesis of (-)-tetrabenazine via continuous crystallization-induced diastereomer transformation.

A multi-well continuous CIDT approach with inline racemization of the solution phase is presented. Using two in-house built PATs and a flow reactor, we were able to successfully crystallize an enantiopure salt of TBZ, the active metabolite of the tardive dyskinesia drug valbenazine. Despite discovering an undesired racemic solid phase, inline racemization combined with careful control of crystallization conditions allowed for multigram quantities of enantiopure material to be harvested using our setup. Critically, this control was made possible by the use of PATs to observe and quantify the composition of both the solid and solution phases.

Chemoenzymatic enantioselective route to get (+) and (−) 4-acetoxy-azetidin-2-one by lipase-catalysed kinetic resolution and their applications

4-Acetoxy-azetidin-2-one is an extremely useful intermediate widely applied for the synthesis of several biologically active β-lactam compounds. However, it is available as a racemic mixture that could limit its application in the synthesis of enantiopure products. Herein we evaluated the use of lipases in a kinetic resolution (KR) process to finally obtain 4-acetoxy-zetidin-2-one as separated pure enantiomers. From a preliminary screening on a set of commercial enzymes, Pseudomonas fluorescens emerged as the most suitable lipase that allowed to obtain good conversions and excellent enantiomeric excesses. On the enantiomerically pure 4-acetoxy-azetidin-2-ones some nucleophilic substitutions and N-thio-alkylation reactions were tested in order to evaluate the stereochemical integrity at the C-4 position.

A Direct Organocatalytic Enantioselective Route to Functionalized trans-Diels-Alder Products Having the Norcarane Scaffold.

An enantioselective methodology to construct trans-Diels-Alder scaffolds by organocatalysis with excellent selectivity, high yield and up to five contiguous stereocenters is presented. The reaction concept integrates the halogen effect and a novel discovered pseudo-halogen effect to direct an endo-selective, secondary-amine catalyzed Diels-Alder reaction allowing for the subsequent formation of trans-Diels-Alder cycloadducts featuring the norcarene scaffold. The methodology relies on the reaction between an in situ generated trienamine and an α-brominated or α-pseudo-halogenated enone to form a fleeting cis-Diels-Alder intermediate. The endo-transition state-enhanced by the (pseudo-)halogen effect-sets the stereochemistry that allows for a subsequent SN 2-like reaction at a tertiary center to obtain the trans-Diels-Alder scaffold. The mechanism was investigated and supported by experimental results as well as computational studies.

A Direct Organocatalytic Enantioselective Route to Functionalizedtrans‐Diels–Alder Products Having the Norcarane Scaffold

AbstractAn enantioselective methodology to construct trans‐Diels–Alder scaffolds by organocatalysis with excellent selectivity, high yield and up to five contiguous stereocenters is presented. The reaction concept integrates the halogen effect and a novel discovered pseudo‐halogen effect to direct an endo‐selective, secondary‐amine catalyzed Diels–Alder reaction allowing for the subsequent formation of trans‐Diels–Alder cycloadducts featuring the norcarene scaffold. The methodology relies on the reaction between an in situ generated trienamine and an α‐brominated or α‐pseudo‐halogenated enone to form a fleeting cis‐Diels–Alder intermediate. The endo‐transition state‐enhanced by the (pseudo‐)halogen effect‐sets the stereochemistry that allows for a subsequent SN2‐like reaction at a tertiary center to obtain the trans‐Diels–Alder scaffold. The mechanism was investigated and supported by experimental results as well as computational studies.

Stereoselective synthesis of the C16–C25 fragment of alchivemycins A and B

An enantioselective route for the efficient synthesis of the key C16–C25 fragment of alchivemycins A and B is described. The route features an Achmatowicz-type rearrangement of furan and a highly enantio- and diastereoselective dihydroxylation as key reactions.

Asymmetric synthesis of six tetrahydroisoquinoline natural products through α-amination of an aldehyde

An enantioselective route towards the synthesis of C-1 substituted tetrahydroisoquinoline natural products is reported. Six different natural products are synthesized from a single aldehyde using proline-catalyzed asymmetric α-hydrazination reaction as the key step. The highly enantioselective introduction of an amino group is exploited to synthesize (−)-calycotomine, (−)-salsolidine, (−)-carnegine, (+)-homolaudanosine, (+)-homoprotoberberine and (+)-crispine A.

Enantioselective Synthesis Muqubilin and Negombatoperoxides B and C/D.

Muqubilin, negombatoperoxide B, and negombatoperoxide C/D were synthesized through enantioselective routes, with the quaternary center derived from a peroxy chiral building block of known absolute configuration. The C-2/C-3 stereogenic centers were introduced by asymmetric aldol condensation, and the 1,2-dioxane ring was constructed via an intramolecular alkylation of a hydroperoxide with a mesylate. The synthetic samples showed physical and spectroscopic data consistent with those reported in the literature and thus verified the configurations of the natural products. A potentially more expeditious enantioselective entry to the 1,2-dioxane-aldol moiety (C-1 to C-6) of such cyclic peroxides was also briefly explored, where the C-2/C-3 stereogenic centers were installed through a [2+2] cycloaddition and the 1,2-dioxane ring was closed via an intramolecular alkylation coupled with an alkyl-oxygen cleavage of a β-lactone.

A Reliable Enantioselective Route to Mono-Protected N1-Cbz Piperazic Acid Building Block.

The chiral N1-Cbz, N2-H derivative of the piperazic acid monomer is a valuable building block in the total synthesis of natural products, comprising this nonproteinogenic amino acid. In that context, we wish to report an improved synthetic protocol for the synthesis of both (3R)- and (3S)-piperazic acids bearing the carboxybenzyl protecting group (Cbz) selectively at the N1 position. Our method builds on previously reported protocols, circumventing their potential shortcomings, and optimizing the ultimate selective deprotection at the N2 position, thus, offering an efficient and reproducible pathway to suitably modified piperazates in high optical purity.