Nickel(II)-Catalyzed [3 + 2] Cycloaddition of Nitrones and Allenoates to Access N-Vinylindoles and N-Vinylpyrroles

Synthesis of Benzazepines Bearing Three Contiguous Carbon Stereocenters through Pd(II)-Catalyzed [3 + 2] Cycloaddition of N-Aryl Nitrones with Allenoates

A cascade reaction of Pd(II)/dppben-catalyzed [3 + 2] cycloaddition of N-aryl nitrones with allenoates and sequential reduction has been developed for the synthesis of functionalized benzazepines bearing three contiguous carbon stereocenters in moderate to good yields ranging from 15 to 82% and high diastereoselectivity. The obtained benzazepines could be converted into various benzazepine scaffolds, and an estrone-derived benzazepine scaffold was prepared over four steps from estrone. More importantly, chiral benzazepine bearing three contiguous carbon stereocenters could be obtained in 88% ee value with chiral auxiliary.

Asymmetric [3 + 3] cycloaddition of cinnamaldehyde-derived N-aryl nitrones with 2-indolemethanols enabled by chiral phosphoric acid

We described a chiral phosphoric acid (CPA) catalyzed asymmetric [3 + 3] cycloaddition of cinnamaldehyde-derived N-aryl nitrones with 2-indolylmethanols to prepare various indole-fused 1,2-oxazines in high yields (up to 96%) with excellent enantioselectivity (>99% ee). Control experiments indicate that hydrogen bonding plays important roles in controlling the enantioselectivity of products. This strategy provides an efficient pathway to construct enantioenriched indole-fused 1,2-oxazines from N-aryl nitrones with 2-indolylmethanols.

Synthesis of Quinolinoneylnitrones and Coumarinylnitrones via a Cascade Hydroamination and Aza-MBH-Type Reaction

Nitrones are quite useful intermediates and have been broadly applied in organic synthesis, drug discovery, and photochemistry research. Many functional nitrones have been successfully prepared using various strategies. In this work, an efficient method for synthesizing novel quinolinoneylnitrone and coumarinylnitrone derivatives was developed. Preliminary mechanistic research suggests that this protocol included a cascade hydroamination and aza-MBH-type reaction.

Mechanoredox/Nickel Co-Catalyzed Cross Electrophile Coupling of Benzotriazinones with Alkyl (Pseudo)halides

An air-tolerant mechanoredox/nickel cocatalyzed cross electrophile coupling of benzotriazinones with alkyl (pseudo)halides is developed by liquid-assisting grinding in the presence of manganese powders and strontium titanate as a reductant and a cocatalyst, respectively. Mechanical activation of metal surfaces via ball milling eliminates the chemical activator for manganese, while mechanoredox cocatalysis of strontium titanate remarkably improves the aryl/alkyl cross electrophile coupling via piezoelectricity-mediated radical generation from alkyl halides. Both benzotriazinones and alkyl (pseudo)halides display reactivities in the mechanoredox/nickel cocatalysis different from those of conventional thermal chemistry in solution. The scope of the reaction is demonstrated with 26 examples, showing a high chemoselectivity of bromides vs chlorides.

Catalytic asymmetric transformation of nitrones and allenes to dihydropyridoindoles via chiral N,N'-dioxide/cobalt(II) catalysis

A chiral N,N'-dioxide/cobalt(II) complex catalytic system is developed to promote the multistep cascade reaction of α,β-unsaturated-N-aryl nitrones with allenes, giving a variety of chiral dihydropyridoindoles in moderate to good yields with excellent dr and ee values. Mechanistic studies support a [3+2] cycloaddition/[3,3]-rearrangement/retro-Mannich process.