Silver‐Catalyzed [3+2] Cycloaddition of Azomethine Ylides with Isocyanides for Imidazole Synthesis

Abstract

As ilver-catalyzed aerobic oxidative [3+ +2] cycloaddition of azomethine ylides with aryl or heteroaryl isocyanides hasbeen developed. Thereaction represents an ovel protocolf or the efficienta nd practical synthesiso f1 ,2-diarylimidazoles bearing a broad range of substituents in good to excellent yields under mild conditions.T he practicability of this cycloaddition was shown by ag ram-scale synthesis and ad ouble cycloaddition for the construction of highly conjugated polyarylimidazole systems.

Tandem Cyclization−Annulation of α‐Acidic Isocyanides with 2‐Methyleneaminochalcones: Synthesis of Pyrrolo[2,3‐c]quinoline Derivatives

“…[16,17] Accordingly, a range of structurally complex heterocycles, including pyrrolizidines, [ were efficiently constructed from the domino reaction of a-acidic isocyanides with all-carbon 1,4-, 1,5-or 1,7dielectrophiles (Scheme 1, top). In continuation of our studies on isocyanide-based reactions, [18] as well as inspired by Xu's work [19] wherein 2-methyleneaminochalcones were used as aza-dielectrophiles, we herein report the tandem cyclization-annulation of a-acidic isocyanides with 2-methyleneaminochalcones for the straightforward and efficient synthesis of 3H-pyrrolo [2,3-c]quinolines and tetrahydro-3H-pyrrolo[2,3-c]quinolines, respectively (Scheme 1, bottom). Both the aromatic and partially aromatic tricyclic pyrroloquinolines were efficiently assembled by simultaneous formation of the pyridine and pyrrole rings in a single operation.…”

“…On the basis of above observations and the related work, [16][17][18][19]21] a possible pathway for this domino reaction is proposed in Scheme 5. The tandem cyclization-annulation may involve the following domino sequence: Michael addition of isocyanides 2 to 2methyleneaminochalcone 1 under basic conditions provides the anion I; [21] proton shift takes place to generate anion II, followed by intramolecular Mannich reaction to form the bicyclic nitrogen anion III (this step may be reversible based on the results of eq 6 in Scheme 4); sequential proton shift and cyclization give the tricyclic intermediate V, which undergoes 1,3-proton shift to produce tetrahydropyrroloquinolines 4 (EWG = CO 2 Et) or intermediate VI (EWG = Ts).…”

Silver‐Induced [3+2] Cycloaddition of Isocyanides with Acyl Chlorides: Regioselective Synthesis of 2,5‐Disubstituted Oxazoles

“…One pathway is similar to El Kaïm's work (Pathway B) in which species 8 undergoes a deprotonation sequence to form nitrilium adduct 10 that subsequently cyclizes to form the desired product 3 . The other pathway (Pathway A) involves intramolecular nucleophilic addition from 8 to generate the cyclized cationic intermediate 9 . Finally, the target product 3 is produced via a proton shift process along with regeneration of the AgMOF catalyst .…”

Synthesis of π-Extended Imidazoles by 1,3-Dipolar Cycloaddition of Polycyclic Aromatic Azomethine Ylides with Nitriles

“…Aryl cyanides (Ar–CN) were also reported to undergo a 1,3-dipolar addition with active azomethine ylides; in this case, the presence of strong electron-withdrawing groups such as cyano, trifluoromethyl, and halo groups on the aryl substituent of aryl cyanides is required (Scheme B) . Electron-deficient aryl isocyanides ( ) were reported to afford imidazole derivatives . In all cases, the limitation in substrate to electron-deficient dipolarophiles only is reasonable given that azomethine ylides are usually electron-rich chemical species.…”