Synlett

An organocatalytic asymmetric oxa-Michael–Michael reaction of 3-aryl-2-nitroprop-2-enols with alkylidene pyrazolones has been developed. This report describes the first use of a 3-aryl-2-nitroprop-2-enol as an O-nucleophile in enantioselective catalysis. With 10 mol% of a quinine-derived squaramide catalyst, a variety of spirotetrahydropyranopyrazolones were obtained in moderate yields, excellent diastereomeric ratios, and high to excellent enantioselectivities under mild reaction conditions.

C4-Functionalized indole scaffolds are ubiquitous in natural products, bioactive compounds, and pharmaceuticals. Much effort has thus been made to develop effective synthetic strategies for C4 functionalization of the indole core. Among them, chelation-assisted synthetic approaches using transition-metal catalysis for the C4-selective C–H functionalization of indole is attractive. This account highlights progress made in C4-carbon–carbon bond formation of indole using directing-group-assisted transition-metal-catalyzed C–H functionalization (up to May 2022). These studies have been performed using Ru, Rh, Pd and Ir-based catalytic systems, while attention has been focused on the use of first-row abundant catalytic systems.1 Introduction2 Alkylation3 Acylation4 Alkenylation5 Alkynylation6 Allylation7 Annulation8 Arylation9 Conclusion and Outlook

A bicyclo[4.1.0]heptane framework consisting of cis-fused cyclopropane and cyclohexane rings is found in several bioactive compounds. Given the symmetry of this core, catalytic desymmetrization can be considered as the most straightforward strategy for its enantioselective synthesis. Known desymmetrization reactions of meso-bicyclo[4.1.0]heptane derivatives proceed with opening of the cyclopropane ring. We now report the first ring-retentive desymmetrization of bicyclo[4.1.0]heptane derivatives, namely meso-cyclopropane-fused cyclohexene-1,4-diones, through a formal C(sp2)-H alkylation using a nitroalkane as the alkylating agent. This reaction is catalyzed by a dihydroquinine-derived bifunctional tertiary aminosquaramide and generates the products with up to 97:3 er. An application of this reaction is demonstrated by the first catalytic enantioselective synthesis of the natural product (–)-car-3-ene-2,5-dione.

A one-pot asymmetric aminoarylation reaction has been executed for the synthesis of trans-4-amino-5-aryltetrahydrobenzo[c]azepines with excellent diastereo- and enantioselectivity (dr > 99: 1; ee ≤97%). The reaction progresses through aziridination of prochiral N-tosyl-N-cinnamylbenzylamines, followed by an intramolecular 7-endo-tet Friedel–Crafts cyclization of the tethered aziridines generated in situ, where the combination of Cu(OTf)2 as a catalyst and PhINNs as a nitrene source was found to be effective. A chiral indenyl bis(oxazoline) was shown to be an efficient ligand for the catalytic enantioselective version of this one-pot transformation. This 7-endo-tet cyclization is contrary to the Baldwin cyclization rules.

A well-known squaramide-cinchonine organocatalyst was immobilized in a controlled way onto three types of commercial porous glass beads EziG™ (EziG OPAL, EziG Amber, and EziG Coral) and applied in asymmetric Michael reactions. The performance of the immobilized catalysts was evaluated under batch and continuous-flow conditions, showing promising results in both approaches. In batch reactions, 0.8 and 1.6 mol% of the immobilized cinchonine-squaramide provided the products with excellent yields (up to 99%) and enantioselectivities (up to 99% ee). These excellent results were also verified in the case of continuous-flow reactions, where also 0.8 and 1.6 mol% of the catalyst immobilized onto the glass beads afforded the product with extraordinary yields (up to 99%) and very high enantioselectivities (up to 97% ee). The immobilized catalysts could be recycled (up to seven cycles) using both approaches.

Stereoselective synthesis of key acyclic skeleton of structurally challenging and biologically active boscartin A possessing six stereogenic centers, among which three are tertiary, has been achieved for the first time. The synthetic study comprises the Sharpless asymmetric epoxidation (SAE) followed by stereoselective epoxide opening for installation of C-11 and C-12 centers, Meyer–Schuster rearrangement followed by intramolecular oxa-Michael addition for construction of C-1 center, SAE followed by CBS reduction and subsequent cycloetherification for stereoselective generation of C-3, C-4, and C-7 centers, Gilman reaction for introduction of C-9 olefin and Grignard reaction for installation of C-8 olefin.

A simple and transition-metal-free HFIP-induced allylation reaction of tertiary allylic alcohols with thiols or sulfonyl hydrazine derivatives was reported for the efficient and highly selective synthesis of allylic sulfides and allylic sulfones. Herein, HFIP played a vital role in not only activating the allylic alcohol, but also stabilizing the allylic cation intermediate to accelerate the subsequent transformations.

As a special class of cyclopropanes, gem-difluorinated cyclopropanes have many fascinating properties as a result of the gem-difluoro substitution; thus, their reactions have received much attention from the synthetic chemistry community. Recently, gem-difluorinated cyclopropanes have gradually emerged as a type of novel and unique fluorinated allylic synthon in cross-coupling reactions for the synthesis of monofluoroalkenes. Herein, we briefly summarize recent advances in transition-metal-catalyzed reactions of gem-difluorinated cyclopropanes.1 Introduction2 Palladium-Catalyzed Reactions with Linear Selectivity3 Palladium-Catalyzed Reactions with Branched Selectivity4 Other Metal-Catalyzed Reactions5 Conclusions

Domino conjugate addition/inert-bond activation is a useful strategy for improving the efficiency of synthesis. We summarize reports on domino conjugate addition/inert-bond activation and its applications in the rhodium-catalyzed ring-expansion and ring-opening reactions of azetidines.1 Introduction2 Rhodium-Catalyzed Domino Conjugate Addition/β-C Cleavage/ Protonation3 Rhodium-Catalyzed Domino Conjugate Addition/N-Directed α-C(sp3)–H Activation4 Conclusion

We reported a nickel-catalyzed enantioconvergent deaminative alkylation of α-amino acid derivatives with unactivated olefins, providing an efficient and convenient access to a range of α-enantioenriched amides. This method represents the first example of enantioselective deaminative functionalization with racemic amine precursors and features in mild conditions and broad substrate scope. New sterically encumbered bis(oxazoline) ligand was developed to improve both reactivity and enantioselectivity, which is key to the success of this reaction.