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

Abstract

A variety of N-vinylindoles and N-vinylpyrroles were prepared in moderate to good yields through the nickel(II)catalyzed [3 + 2] cycloaddition of α,β-unsaturated nitrones with allenoates under mild reaction conditions. A rational mechanism for the formation of N-vinylindoles was proposed based on the 18 O-labeled experiments and key intermediates detected by highresolution mass spectrometry trace experiments. The present method highlights a nickel(II)-controlled cyclization, atomeconomical reaction, broad substrate scope, good functional group tolerance, and high Z-stereoselectivity for the enamine bond.

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

“…Chemicals obtained from commercial sources were used as received. Nickel complex Ni­(bpy)­Cl 2 and benzotriazinones were prepared according to known procedures (see the SI for details). The reaction progress was monitored by TLC.…”

Copper(II)‐Catalyzed Cascade Reactions of N‐Aryl Nitrones and Disubstituted Allenoates to Prepare [1,3]Oxazino[3,2‐a]indolines and Dihydropyrido[1,2‐a]indolines

“…[10] In 2021, our group reported a nickel(II)-catalyzed [3 + 2] cycloaddition of N-aryl or N-vinyl-α,β-unsaturated nitrones with monosubstituted allenoates to prepare N-vinylindoles and Nvinylpyrroles in good yields. [11] However, up to now, the reaction of N-aryl-α,β-unsaturated nitrones with disubstituted allenoates is still unexplored clearly. The control of regioselective cyclization after [3,3]-rearrangement, diastereoselectivity of indoline products, and scaffold diversity of indolines are still challenging.…”

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

“…Based on the above experiments, previous work 6,12 and the absolute configuration of the products, a possible mechanism was proposed (Scheme 5). Initially, α , β -unsaturated- N -aryl nitrone and allene underwent [3+2] cycloaddition, and subsequent [3,3]-rearrangement to afford the benzazepine intermediate, which can undergo either retro Michael opening to form the byproduct dihydrocarbazole (path a) or retro-Mannich opening to form the dihydropyridoindole (path c).…”