Stereodivergent Synthesis of Enantioenriched γ-Butyrolactones Bearing Two Vicinal Stereocenters Enabled by Synergistic Copper and Iridium Catalysis

Diastereodivergent Aldol-Type Coupling of Alkoxyallenes with Pentafluorophenyl Esters Enabled by Synergistic Palladium/Chiral Lewis Base Catalysis

As a fundamental and synthetically useful C-C bond formation reaction, the aldol reaction is one of the most versatile transformations in organic synthesis. However, despite extensive research on asymmetric versions of the reaction, a unified method for stereoselective access to the complementary syn and anti diastereomeric products remains to be developed. In this study, we developed a synergistic palladium/chiral Lewis base system that overcomes the inherent diastereoselectivity bias of aldol reactions and, as a result, allowed us to achieve the first diastereodivergent coupling reactions of alkoxyallenes with pentafluorophenol esters. Computational studies suggest a mechanism involving an intermolecular protonative hydropalladation pathway rather than a palladium-hydride migratory insertion pathway. The origin of the stereochemistry for this synergistic catalysis system is rationalized by DFT calculations.

Stereodivergent Synthesis of Enantioenriched α-Deuterated α-Amino Acids via Cascade Cu(I)-Catalyzed H-D Exchange and Dual Cu- and Ir-Catalyzed Allylation

A one-pot Cu-mediated H-D exchange with inexpensive heavy water as the deuterium source, followed by Cu- and Ir-catalyzed stereodivergent allylic alkylation, has been developed, providing efficient access to enantioenriched α-deuterium-labeled α-amino acids from readily available glycine imine esters in a high yield with excellent stereoselectivity. High deuterium enrichment, exquisite regioselectivity, precise stereoselectivity control, and operationally convenient procedures make this protocol appealing for the preparation of highly synthetically useful α-deuterated α-amino acids.

Enantioselective Synthesis of Spiroketals and Spiroaminals via Gold and Iridium Sequential Catalysis

The enantioselective cascade reaction between racemic 2-(1-hydroxyallyl)phenols and alkynols/alkynamides was realized by using a gold and iridium sequential catalytic system. In this procedure, the in situ generated exocyclic vinyl ethers or enamides undergo the asymmetric allylation/spiroketalization with π-ally-Ir amphiphilic species, which provides an efficient and straightforward access to spiroketals and spiroaminals with excellent enantioselectivities. Moreover, racemic 2-(1-hydroxyallyl)anilines were also suitable in this reaction along with a kinetic resolution process, affording enantioenriched spiroaminals and 2-(1-hydroxyallyl)anilines in good yields. The synthetic utility of this method has been demonstrated by efficient enantioselective synthesis of the analogue of Paecilospirone.

A new type of δ-vinylvalerolactone for palladium-catalyzed cycloaddition: synthesis of nine-membered heterocycles

In this paper, a new type of δ-vinylvalerolactone was designed and synthesized, and used as a new precursor in Pd-catalyzed [6+3] cycloaddition with azomethine imines, leading to nine-membered 1,2-dinitrogen-containing heterocycles in 77-98% yields with >20 : 1 d.r. These nine-membered ring-fused products were further transformed into unusual tetracyclic bridged-ring compounds without loss of the diastereoselectivities.

Pd-Catalyzed [4 + 2] cycloaddition of methylene cyclic carbamates with dihydropyrazolone-derived alkenes: synthesis of spiropyrazolones

In this paper, a palladium-catalyzed [4 + 2] cycloaddition of 5-methylene-1,3-oxazinan-2-ones with 4-arylidene-2,4-dihydro-3H-pyrazol-3-ones has been developed to produce spiropyrazolones in high yields with excellent diastereoselectivities in nearly all cases. The cycloaddition reaction was scaled-up without significant loss of yield, and its synthetic utility has been demonstrated by further transformations of the products. The reaction type of N-Ts cyclic carbamates under palladium catalysis was extended to include [4 + 2] cycloaddition for the first time.

Iridium-Catalyzed Asymmetric Allylic Substitution of Methyl Azaarenes

Herein, an Ir-catalyzed asymmetric allylic substitution reaction of methyl azaarenes is described. Azaarenes such as (benzo)thiazole, oxazole, benzoimidazole, pyridine, and (iso)quinoline are all tolerated. The corresponding chiral azaarene derivatives are obtained in good yields with high enantioselectivity (up to 96 % yield and 99 % ee). The utilization of the Knochel reagent TMPZnBr⋅LiBr warrants the in situ formation of benzylic nucleophiles without additional activating reagents. ¹ H NMR studies suggested a two-fold function of the Knochel reagent in this reaction. The synthetic utility of this method has been showcased by a concise enantioselective synthesis of an allosteric protein kinase modulator.

Stereodivergent synthesis of enantioenriched azepino[3,4,5-cd]-indoles via cooperative Cu/Ir-catalyzed asymmetric allylic alkylation and intramolecular Friedel-Crafts reaction

The development of enantioselective annulation reactions using readily available substrates for the construction of structurally and stereochemically diverse heterocycles is a compelling topic in diversity-oriented synthesis. Herein, we report efficient catalytic asymmetric formal 1,3-dipolar (3 + 4) cycloadditions of azomethine ylides with 4-indolyl allylic carbonates for the construction of azepino[3,4,5-cd]-indoles fused with a challenging seven-membered N-heterocycle, a frequently occurring tricyclic indole scaffold in bioactive compounds and pharmaceuticals. Through cooperative Cu/Ir-catalyzed asymmetric allylic alkylation followed by intramolecular Friedel-Crafts reaction, an array of azepino[3,4,5-cd]-indoles were obtained in good yields with excellent diastereo-/enantioselective control. More importantly, the full stereodivergence of this transformation was established via synergistic catalysis followed by acid-promoted epimerization, and up to eight stereoisomers of the cycloadducts bearing three stereogenic centers could be predictably achieved from the same set of starting materials for the first time. Quantum mechanical computations established a plausible mechanism for the synergistic Cu/Ir catalysis to stereodivergently introduce two vicinal stereocenters whose stereochemical information is remotely delivered across the fused azepine ring to control the third chiral center. Epimerization of the last center involves protonation-enabled reversal of the thermodynamically controlled relative configuration.

Asymmetric Synthesis of Chiral Aza-macrodiolides via Iridium-Catalyzed Cascade Allylation/Macrolactonization

Iridium-catalyzed cascade allylation/macrolactonization between vinylethylene carbonate (VEC) and isatoic anhydride derivatives was successfully developed, readily generating a wide range of C₂-symmetric chiral macrodiolides bearing 14-membered rings in moderate to good yields with excellent diastereoselectivities and enantioselectivities (generally 99% ee). Control experiments revealed that racemic VEC as the precursor of electrophilic iridium-π-allyl species underwent kinetic resolution process. This expedient protocol features easily available substrates, excellent stereoselective control, and high step economy.

Iridium-catalyzed asymmetric double allylic alkylation of azlactone: efficient access to chiral α-amino acid derivatives

An unprecedented Ir-catalyzed enantioselective double allylic alkylation of less bulky cyclic imine glycinate (azlactone) was rationally designed and developed, providing various bisallylated chiral amino acid derivatives. Control experiments revealed that this transformation proceeds in a sequential manner featuring quasi-dynamic kinetic resolution of the initially-formed monoallylation intermediates.

Synthesis of pyranopyrazoles with a chiral quaternary carbon stereocenter via copper-catalyzed enantioselective [3 + 3] cycloaddition

A copper-catalyzed enantioselective [3 + 3] cycloaddition of propargyl carbonates and pyrazolones has been disclosed. This reaction provided an efficient route to synthesize pyranopyrazoles containing a chiral quaternary carbon stereocenter in good yields with good to excellent enantioselectivities. In addition, the hydroxyl group in the products could be conveniently transformed into a variety of functional groups, such as aldehyde, nitrile, alkene, ester and amide groups, which further increased the synthetic value of this reaction.

Stereodivergent synthesis via iridium-catalyzed asymmetric double allylic alkylation of cyanoacetate

Methods that enable the rapid construction of multiple C–C bonds using a single catalyst with high diastereo- and enantio-control are particularly valuable in organic synthesis. Here, we report an Ir-catalyzed double allylic alkylation reaction in which bisnucleophilic cyanoacetate reacted successionally with electrophilic π-allyl-Ir species, producing various pseudo-C₂-symmetrical cyanoacetate derivatives in high yield with excellent stereocontrol. More challenging sequential allylic alkylation/allylic alkylation with two distinct allylic carbonates that can deliver the corresponding products bearing three contiguous tertiary–quaternary–tertiary stereocenters was also developed by using a modified catalytic system, which is revealed to be associated with the quasi-dynamic kinetic resolution of the initially formed diastereomeric monoallylation intermediates. Notably, stereodivergence for this sequential process depending on a single iridium catalyst was successfully realized, and up to six stereoisomers could be predictably prepared by combining the appropriate enantiomer of the chiral ligand for the iridium catalyst and adjusting the adding sequence of two distinct allylic precursors.

Ir-catalyzed asymmetric double AAA reaction of cyanoacetate was developed, affording cyanoacetate derivatives in high yield with excellent stereocontrol. Notably, quasi-DKR is involved in the sequential protocol with two distinct allylic carbonates.

A cooperative Pd/Co catalysis system for the asymmetric (4+2) cycloaddition of vinyl benzoxazinones with N-acylpyrazoles

Transition metal-catalyzed cycloaddition has been established as a powerful tool for heterocycle synthesis. Despite impressive advances, the exploitation of new catalysis strategies and systems is still highly significant to enrich the heterocycle family. Herein, we disclosed a cooperative catalysis system merging an achiral Pd catalyst and a chiral Co catalyst for the asymmetric [4+2] cycloaddition between vinyl benzoxazinones and N-acylpyrazoles. Chiral tetrahydroquinolines bearing two contiguous, unusual cis-configured stereocenters were produced in high yields and enantio- and diastereoselectivities. The pyrazole directing group can be easily converted into many other functional groups, thus demonstrating the flexibility of the present methodology.