Tandem Synthesis of Pyrrolo[2,3-b]quinolones via Cadogen-Type Reaction

Abstract

A tandem [3 + 2] cycloaddition/reductive cyclization of nitrochalcones with activated methylene isocyanides for the efficient synthesis of pyrrolo[2,3-b]quinolones is reported. In this reaction, the in situ generated dihydropyrroline acts as the internal reductant to convert the nitro into an electrophilic nitroso group, which undergoes subsequent C-N bond formation. Transition-metal-free, simple experimental procedure and ready accessibility of starting materials characterize the present transformation.

External Reductant‐free Stepwise [3+2] Cycloaddition/Reductive Cyclization from 2‐Nitrochalcones and Isocyanides: Synthesis of Pyrrolo[3,4‐c]quinoline N‐oxides

“…On the basis of the aforementioned results and precedent literaturereports, [11][12][13][14] a possible mechanistic pathway for the generation of pyrrolo [3,4-c]quinoline N-oxides 4 is proposed as shown in Scheme 6. The stepwise reaction initiating from 1 a and 2 a through [3 + 2] cycloaddition to form dihydropyrrole 3 a.…”

“…The following process may involve two redox-neutral processes, the first process is the generation of nitroso intermediate IV, the dihydropyrroline moiety of 3 a acts as the in situ formed internal reductant to convert the nitro group into reactive nitroso functionality. The specific process is deprotonation of 3 takes place to form anion I, then intramolecular cyclization of intermediate I produces the intermediate II, [13,14] then cope-type elimination [18] of II forms anion III, under dehydroxylation and proton shift to form the reactive nitroso intermediate IV. With regard to the second redox-neutral process, the synthesis of pyrrolo [3,4-c]quinoline Noxides 4 a starting from nitroso intermediate IV was a reduction cyclization process, but abnormally happened in an external reductant-free condition.…”

Recent Advances in the Chemistry of Isocyanides with Activated Methylene Group

“…A tandem [3+2] cycloaddition/reductive cyclization of nitrochalcones with activated methylene isocyanides 1 for the efficient synthesis of pyrrolo[2,3‐ b ]quinolones 48 was reported by Zhichen Lin et al [ 26 ] In this reaction, in situ generated dihydropyrroline acted as the internal reductant to convert the nitro into an electrophilic nitroso group, which underwent subsequent C–N bond formation (Scheme 23). It should be noted that a broad scope of both nitrochalcones and isocyanides can be used in this reaction.…”

Intermediate formation enabled regioselective access to amide in the Pd-catalyzed reductive aminocarbonylation of olefin with nitroarene

“…Nitroarenes are generally cheaper, more readily available, and more functionally compatible than anilines as nitrogen sources [1][2][3][4]. Therefore, using nitroarenes as starting molecules is advantageous for preparing nitrogen-containing functional molecules in proper cascade reactions [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Notably, nitroarenes can be reduced to several corresponding N-species under different conditions [5][6][7][8][9]19], which provide various synthesis routes from nitroarenes via in situ intermediate for-mation control.…”