Base‐Catalysed (4+2)‐Annulation Between 2‐Nitrobenzofurans and N‐Alkoxyacrylamides: Synthesis of [3,2‐b]Benzofuropyridinones

Abstract

An efficient protocol for base‐catalysed (4+2) annulation between 2‐nitrobenzofuran and N‐alkoxyacrylamide was developed. The corresponding 1‐alkoxy‐3,4‐dihydrobenzofuro[3,2‐b]pyridin‐2(1H)‐ones were obtained in high to excellent yields by organic base catalysis. In addition, a dearomative nitrotetrahydrobenzofuro[3,2‐b]pyridin‐2(3H)‐ones were also obtained in high yields in the presence of an inorganic base. The advantages of this methodology include easily accessible starting materials, simple operational procedures, broad substrate scope, and synthetically useful yields at milder reaction conditions.

Formal Alkenylation and Amination of 2‐Nitrobenzofurans with Fumaric Acid Amide Ester under Metal‐Free Conditions

“…Very recently, Sun and co‐workers reported a dearomative [3+2] cycloaddition reaction between 3‐nitro‐indoles and fumaric acid amide esters (Scheme 1c) [7] . Contemporarily, we reported a base catalyzed dearomative (4+2) annulation between 2‐nitrobenzofuran and N‐alkoxyamides (Scheme 1d, left) [8] . In continuation of our earlier work, herein, we report a serendipitous two‐fold formal C2‐alkenylation and C3‐amination of benzofuran scaffold under ambient reaction conditions by employing 2‐nitrobenzofuran and fumaric acid amide ester (Scheme 1d, right).…”

Copper-Catalyzed Annulation of Electrophilic Benzannulated Heterocycles with 2-Aminopyridine and 2-Aminoquinoline: Direct Access toward Polyring-Fused Imidazo[1,2-a]pyridines

“…Based on the above observations and literature precedents, , we propose a mechanism for the annulation reaction, as shown in Scheme . The first step is the Michael addition of 2-aminopyridine to the C-2 of 3-nitroindole wherein the Cu-catalyst (acting as a Lewis acid) coordinates with the oxygen of the nitro group in 1a .…”

“…This step affords the intermediate 3a′ , which we could isolate as depicted in Scheme i. This is followed by the elimination of nitrous acid and subsequent aromatization to furnish indole-fused imidazo­[1,2- a ]­pyridine 3a …”

Organocatalytic cascade nucleophilic/aza-Michael addition reactions: metal-free catalytic strategy for the synthesis of hydantoins

“…On the one hand, N -alkoxy acrylamides (R = H, alkyl or aryl groups) are preferable to function as 1,4- N , C β -synthon to furnish [4 + 2] annulation reactions. 23 On the other hand, β-ester group tethered N -alkoxy acrylamides (known as fumaric acid amide esters) also worked as a 1,3- N , C α -synthon to undergo [3 + 2] cycloaddition reactions. 24 However, to the best of our knowledge, these elegant studies were limited to the construction of γ- or δ-lactam scaffolds, the synthetic potential of acrylamides still needs to be further explored.…”