Enantioselective Cyclopropanation of 4‐Nitroisoxazole Derivatives

Organocatalytic Asymmetric Direct Vinylogous Michael Initiated Ring Closure Reaction of 4-Nitroisoxazole Derivatives to 3-Isopropylidene Oxindoles

Herein, we present the first ever use of 3-isopropylidene oxindoles as electrophiles in vinylogous Michael initiated ring closure reaction (MIRC). Among the various alkylidene oxindoles used in enantioselective spirocyclization reactions, isopropylidene oxindoles are the least explored to date. The competing reactivity of isopropylidene oxindoles (electrophilicity vs nucleophilicity) in the presence of a chiral organocatalyst is controlled by the logical selection of a more reactive nucleophile. The methodology produces a library of densely substituted highly enantioenriched spirocyclopropyl oxindoles with excellent yield and stereoselectivities. Moreover, the first enantioselective synthesis of HIV-1 NNRT inhibitor indicates the importance of our synthesized spiro-cyclopropyl oxindole core.

Stereoselective N-Heterocyclic-Carbene-Catalyzed Formal [4 + 2] Cycloaddition: Access to Chiral Heterocyclic Cyclohexenones

The present study reports an asymmetric NHC-catalyzed formal [4 + 2] cycloaddition of heterocyclic alkenes containing a polarized double bond with an azolium-dienolate intermediate generated from α-bromo-α,β-unsaturated aldehydes without external oxidation of the Breslow intermediate. Heterocyclic cyclohexenones were produced in good isolated yields (typically about 90%) with good stereochemical outcomes (in most cases, dr > 20/1, and ee = 70-99%). The synthetic utility of the protocol was exemplified by the scope of heterocyclic alkenes.

Asymmetric Synthesis of Spiro-3,3'-cyclopropyl Oxindoles via Vinylogous Michael Initiated Ring Closure Reaction

A novel organocatalytic cascade approach for the synthesis of spiro-cyclopropyl oxindole derivatives has been developed. The methodology is based on asymmetric vinylogous Michael addition of 4-nitroisoxazole derivatives to N-Boc isatylidene malonates followed by intramolecular alkylation. Its remarkable stereocontrol, wide substrate scope, and scalability highlight this new developed strategy. Moreover, this work represents the first example of vinylogous Michael initiated ring closure (MIRC) reaction for the synthesis of chiral 3,3'-cyclopropyl oxindole.

Vinylogous Nitro-Haloform Reaction Enables Aromatic Amination

The first example of an aromatic haloform reaction is reported, defining a conceptually new haloform-type approach to the metal-free functionalization of arenes. We demonstrated that heteroarenes bearing a vinylogous nitromethane system, via the stage of a trichloromethane derivative, could undergo aromatic amination to produce N-functionalized arenes in quantitative yields and without the need for transition-metal catalysis. The haloform-type amination was implemented in the development of effective orthogonal N-protection strategies, establishing a new promising N-protecting reagent.

Discovery of 4-nitro-3-phenylisoxazole derivatives as potent antibacterial agents derived from the studies of [3 + 2] cycloaddition

Polysubstituted phenylisoxazoles were designed and synthesized to discover new antibacterial agents via [3 + 2] cycloaddition. Thirty-five compounds with a phenylisoxazole scaffold were characterized by NMR, HRMS, and X-ray techniques. After being evaluated against Xanthomonas oryzae (Xoo), Pseudomonas syringae (Psa), and Xanthomonas axonopodis (Xac), 4-nitro-3-phenylisoxazole derivatives were found to better antibacterial activities. Further studies have shown that the EC₅₀ values of these compounds were much better than that of the positive control, bismerthiazol.

Thirty-five compounds with phenylisoxazole scaffold were synthesized via [3+2] cycloaddition. After being evaluated against Xoo, Psa and Xac, 4-nitro-3-phenylisoxazole derivatives were found well antibacterial activities.

Efficient Asymmetric Simmons-Smith Cyclopropanation and Diethylzinc Addition to Aldehydes Promoted by Enantiomeric Aziridine-Phosphines

During an implementation of current research, a set of optically pure chiral aziridines and aziridine imines bearing a phosphine moiety was prepared with high values of chemical yield. The above chiral heteroorganic derivatives were tested for catalytic utility as chiral ligands in asymmetric Simmons-Smith cyclopropanation and asymmetric diethylzinc addition to various aldehydes. Most of the desired products were formed in high chemical yields, with satisfactory values of enantiomeric excess (sometimes more than 90%) and diastereomeric ratios (in case of cyclopropanation reaction).