Regio- and Enantioselective Allylic Amination of Aliphatic MBH Adducts with N-Heteroaromatics

Axially Chiral Phenanthroline Ligand-Enabled Pd-Catalyzed Asymmetric Amination and Alkylation of Aryl-Substituted Morita-Baylis-Hillman Adducts

Highly enantioselective allylic amination and alkylation of racemic sterically hindered aryl-substituted Morita-Baylis-Hillman (MBH) adducts have been achieved by using an in situ formed Pd-catalyst from an axially chiral phenanthroline ligand. This dynamic kinetic asymmetric transformation (DYKAT) is compatible with cyclic and acyclic secondary amines, dialkyl malonates, β-keto esters, acetylacetone, and malononitrile, affording the corresponding chiral products, such as β-amino acid esters, in up to 95% yield and with up to a 99:1 enantiomeric ratio.

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.

Rhodium-Catalyzed Enantioselective Ring-Openings of Oxabicyclic Alkenes with Azole Nucleophiles

We report enantioselective ring-openings of oxabicyclic alkenes with azole nucleophiles, generating heterocycle-bearing dihydronaphthalene products. Pyrazoles, triazoles, tetrazoles, and benzo-fused derivatives participate in the ring-opening, with the level of regioselectivity depending on the type and substitution pattern of the heterocyclic partner. Electron-withdrawing azole substituents have a beneficial effect, suppressing the unproductive complexation of a nitrogen with the Rh(I)-bis(phosphine) catalyst.

Chiral Phosphine Ligands of COAP and SKP Switched Regiodivergent Asymmetric Allylic Alkylation of MBH Adducts

The palladium-catalyzed highly regioselective asymmetric allylic alkylation of 3'-indolyl-3-oxindole derivatives with Morita-Baylis-Hillman (MBH) carbonates was developed to facilely construct chiral 3,3'-bisindole derivatives under mild reaction conditions. The regioselectivity (α/γ) of MBH carbonates was efficiently switched in the presence of chiral oxalamide phosphine or spiroketal-based diphosphine/Pd(0) complexes as a chiral catalyst. A series of multifunctional 3,3'-bisindole derivatives with all-carbon quaternary stereogenic centers were obtained in high yields with good to excellent enantio-, diastereo-, and regioselectivity. The present process is endowed with some salient features such as broad substrate scope, N-protecting group-free, excellent stereoselectivity, as well as adjustable regioselectivity.

Microfluidics Biocatalysis System Applied for the Synthesis of N-Substituted Benzimidazole Derivatives by Aza-Michael Addition

Benzimidazole scaffolds became an attractive subject due to their broad spectrum of pharmacological activities. In this work, a methodology was developed for the synthesis of N-substituted benzimidazole derivatives from benzimidazoles and α, β-unsaturated compounds (acrylonitriles, acrylate esters, phenyl vinyl sulfone) catalyzed by lipase TL IM from Thermomyces lanuginosus in continuous-flow microreactors. Investigations were conducted on reaction parameters such as solvent, substrate ratio, reaction temperature, reactant donor/acceptor structures, and reaction time. The transformation is promoted by inexpensive and readily available lipase in methanol at 45 °C for 35 min. A wide range of β-amino sulfone, β-amino nitrile, and β-amino carbonyl compounds were efficiently and selectively synthesized in high yields (76–97%). All in all, a microfluidic biocatalysis system was applied to the synthesis of N-substituted benzimidazole derivatives, and could serve as a promising fast synthesis strategy for further research to develop novel and highly potent active drugs.

Electrochemical Enantioselective Dihydroxylation Reaction of N-Alkenyl Nucleobases for the Construction of Chiral Acyclic Nucleosides

A simple and sustainable KI-mediated electrochemical enantioselective dihydroxylation reaction of N-alkenyl nucleobases was developed for the first time in an undivided cell. A series of chiral acyclic nucleosides bearing two...

Construction of Hydrodibenzo[b,d]furan Frameworks from Morita-Baylis-Hillman Carbonates of Isatins and o-Hydroxy Enones via Palladium and Brønsted Base Relay Catalysis

A cascade assembly between isatin-derived Morita-Baylis-Hillman carbonates and o-hydroxybenzylideneacetones has been developed under the relay catalysis of Pd(PPh₃)₄ and DBU, affording a spectrum of 1,2,3,4-tetrahydrodibenzo[b,d]furan architectures incorporating a spirooxindole motif in moderate to good yields with excellent diastereoselectivity. The fused indole analogues were similarly furnished by employing the benzylideneacetones having an o-TsNH group.

Phosphine-Catalyzed Asymmetric Allylic Alkylation of Achiral MBH Carbonates with 3,3'-Bisindolines: Enantioselective Construction of Quaternary Stereogenic Centers

The asymmetric allylic alkylation (AAA) of achiral Morita-Baylis-Hillman (MBH) carbonates with 3,3'-bisindolines under the catalysis of amino-acid-derived bifunctional phosphines was accomplished. With the AAA approach introduced herein, challenging 3,3'-bisindolines bearing an all-carbon quaternary stereocenter (C3a) have been constructed in good yields with good to excellent enantioselectivties. In addition, the synthetic value of this protocol was demonstrated by the facile synthesis of the core skeleton of gliocladin C.

Design, Synthesis, and Activity Evaluation of Novel Acyclic Nucleosides as Potential Anticancer Agents In Vitro and In Vivo

In the present work, 103 novel acyclic nucleosides were designed, synthesized, and evaluated for their anticancer activities in vitro and in vivo. The structure-activity relationship (SAR) studies revealed that most target compounds inhibited the growth of colon cancer cells in vitro, of which 3-(6-chloro-9H-purin-9-yl)dodecan-1-ol (9b) exhibited the most potent effect against the HCT-116 and SW480 cells with IC50 values of 0.89 and 1.15 μM, respectively. Furthermore, all of the (R)-configured acyclic nucleoside derivatives displayed more potent anticancer activity compared to their (S)-counterparts. Mechanistic studies revealed that compound 9b triggered apoptosis in the cancer cell lines via depolarization of the mitochondrial membrane and effectively inhibited colony formation. Importantly, compound 9b inhibited the growth of the SW480 xenograft in a mouse model with low systemic toxicity. These results indicated that acyclic nucleoside compounds are viable as potent and effective anticancer agents, and compound 9b may serve as a promising lead compound that merits further attention in future anticancer drug discovery.

A Type of Structurally Adaptable Aromatic Spiroketal Based Chiral Diphosphine Ligands in Asymmetric Catalysis

ConspectusWhile spectacular successes have been achieved in homogeneous catalysis with the use of achiral diphosphine ligands featuring a wide natural bite angle, such as XantPhos, chiral diphosphines that can induce a large P-M-P bite angle in their transition metal complexes are conspicuously less explored in asymmetric catalysis, probably due to the challenges in the identification and efficient construction of a suitable chiral backbone. In the past decade, a highly efficient synthesis of chiral aromatic spiroketals and the corresponding diphosphine ligands (SKPs) has been developed in this group.Based on a one-pot catalytic tandem double asymmetric hydrogenation-spiroketalization ring-closure reaction sequence, these SKP ligands featuring an extraordinarily long P···P distance and a flexible backbone have been readily prepared in large scale. Remarkably versatile coordination modes have been found in the complexes of SKP with some catalysis-relevant transition metals, for example, Pd, Cu, Au, and Rh. Whereas SKP enforces an unusually large bite angle in [Pd(SKP)Cl₂] and [Cu(SKP)Cl] complexes (160.1° and 132.8°, respectively), it also allows for a bimetallic Au-Au interaction (3.254 Å) in the complex of [Au₂(SKP)Cl₂] or a square-planar coordination geometry for the [Rh(SKP)(cod)]SbF₆ complex. Such an adaptable nature of SKP ligands for transition metal coordination has profound consequences in homogeneous asymmetric catalysis, as demonstrated by their unique performance in several types of catalytic asymmetric reactions. One of the most exciting examples is SKP/Pd-catalyzed asymmetric allylic amination of Morita-Baylis-Hillman (MBH) adducts, in which SKP/Pd complexes demonstrated excellent control of regio- and enantioselectivities and exhibited exceptionally high efficiency (with a TON up to 4750) in the catalysis. SKP ligands have also found a diversity of successful applications in Cu-, Au-, or Rh-catalyzed asymmetric reactions, further attesting their wide utilities in asymmetric catalysis. Overall, this class of readily accessible SKP ligands featuring a chiral aromatic spiroketal skeleton have demonstrated unique adaptable structures in a variety of transition metal complexes and provided outstanding performance in some difficult asymmetric transformations. The works delineated herein would be expected to stimulate further research efforts on the application of this type of chiral ligand and to provide useful clues in the design of new chiral diphosphine ligands with adaptable bite angles for transition metal catalyzed asymmetric reactions.

Palladium-catalyzed asymmetric allylic amination of a vinylethylene carbonate with N-heteroaromatics

Highly enantioselective allylic amination of a vinylethylene carbonate with N-heteroaromatics is enabled by asymmetric palladium catalysis for the synthesis of chiral acyclic nucleosides and isonucleosides.

Palladium-catalyzed stereoselective (3 + 2) cycloaddition of vinylethylene carbonates with cyclic N-sulfonyl ketimines

A diastereoselective (3 + 2) cycloaddition of N-sulfonyl ketimines with vinylethylene carbonates (VECs) in the presence of Pd2dba3·CHCl3 and PPh3 has been developed. The reaction of various substituted VECs and diverse cyclic N-sulfonyl ketimines proceeded smoothly under mild conditions, giving highly functionalized oxazolidine frameworks in good to excellent yields with moderate to good diastereoselectivities. With the use of spiroketal-based diphosphine SKP as a chiral ligand, an asymmetric version of the current (3 + 2) cycloaddition was achieved, and chiral products were obtained in >99% ee in most cases.

Catalytic mutual multicomponent reaction: facile access to α-trifluoromethylthiolated ketones

A multicomponent catalytic reaction between ketones, Morita-Baylis-Hillman (MBH) carbonates and trifluoromethylthiolating agents is devised for straightforwardly accessing two products, α-trifluoromethylthiolated ketones and α-methylene β-amino esters in a one pot fashion. Particularly noteworthy is that the trifluoromethylthiolating reagent is employed as both the nitrogen and SCF3 source initiated by DABCO. This mild one pot strategy enjoys atom- and step-economic attractiveness, for direct introduction of an SCF3 group onto a variety of acyclic ketones, which have been considered as less effective and less developed substrates.

Construction of All-Carbon Chiral Quaternary Centers through CuI -Catalyzed Enantioselective Reductive Hydroxymethylation of 1,1-Disubstituted Allenes with CO2

A catalytic enantioselective construction of all-carbon chiral quaternary centers through reductive hydroxymethylation of 1,1-disubstituted allenes with CO₂ has been developed. In the presence of a copper/Mandyphos catalyst, CO₂ is transformed into an alcohol oxidation level by an asymmetric reductive C-C bond formation with allenes by using hydrosilane (HSi(OMe)₂ Me) as a reductant. The resulting chiral homoallylic alcohols are versatile synthetic intermediates and can be conveniently converted into a variety of useful chiral chemicals.

Dynamic Kinetic Resolution of α-Purine Substituted Alkanoic Acids: Access to Chiral Acyclic Purine Nucleosides

An efficient route to construct chiral acyclic purine nucleoside analogues via dynamic kinetic resolution of α-purine substituted alkanoic acids is reported. Using ( S)-BTM as the catalyst, diverse chiral acyclic purine nucleoside analogues were obtained in moderate to good yields (up to 93%) and high enantioselectivities (up to 98% ee). Chiral acyclic purine nucleosides could be obtained from the esterified products via reduction reaction, which could then be transferred into Tenofovir analogues.

Synthesis of Chiral Acyclic Nucleosides by Sharpless Asymmetric Dihydroxylation: Access to Cidofovir and Buciclovir

An efficient method to construct chiral acyclic nucleosides via Sharpless asymmetric dihydroxylation of N-allylpyrimidines or N-alkenylpurines is reported. A range of chiral acyclic nucleosides with two adjacent hydroxyl groups present on the side chains could be produced in good yields (up to 97% yield) and excellent enantioselectivities (90-99% ee). The synthetic utility of the reaction was demonstrated by the catalytic asymmetric synthesis of ( S)-Cidofovir and ( R)-Buciclovir.

Organocatalytic enantioselective synthesis of acyclic pyrimidine nucleosides by aza-Michael reaction

An efficient diarylprolinol triphenylsilyl ether-catalyzed enantioselective aza-Michael reaction of pyrimidines as N-centered nucleophiles to α,β-unsaturated aldehydes, followed by reduction, provided chiral acyclic pyrimidine nucleosides in good yields (51-78% yields for two steps) and excellent enantioselectivities (91-98% ee). In addition, the chiral acyclic pyrimidine nucleoside having the tert-butyldiphenylsilyl-protected hydroxyl substituent was successfully applied to the synthesis of the corresponding chiral cyclic pyrimidine nucleoside analogue bearing the tetrahydrofuranyl ring.

Interrupted Morita-Baylis-Hillman-Type Reaction of α-Substituted Activated Olefins

It was demonstrated that 3-olefinic oxindoles could generate zwitterionic enolate species with tertiary phosphines and undergo C-C bond formation with various electrophiles in an interrupted Morita-Baylis-Hillman-type reaction manner, followed by a dephosphoration process. Although the in situ formation of phosphorus-ylide intermediates was observed, no Wittig reaction was detected, even in the presence of excess formaldehyde. Moreover, excellent enantioselectivity for the construction of quaternary stereogenic centers was induced with chiral phosphines. Deuterium experiments and density functional theory calculations were conducted to elucidate the reaction mechanism.

The Baylis–Hillman reaction: a new continent in organic chemistry – our philosophy, vision and over three decades of research

This mini review describes in brief the way in which our research has contributed towards the development of the Baylis–Hillman reaction as a powerful tool in synthetic chemistry, offering unending opportunities and intellectual challenges to understand and address the present day requirements in the area of organic chemistry.

Enantioselective and regiodivergent allylation of pyrimidines with terminal allenes: an approach to pyrimidine acyclic nucleosides

An atom-economic addition of pyrimidines to allenes has been developed for the diverse synthesis of branched or linear N-allylpyrimidine analogues.