Synthesis of Azepinoindoles via Rhodium-Catalyzed Formal Aza-[4 + 3] Cycloaddition Reaction of 3-Diazoindolin-2-imines with 1,3-Dienes in One-Pot

Abstract

Rhodium-catalyzed formal aza-[4 + 3] cycloaddition reaction of 3-diazoindolin-2-imines with 1,3-dienes was demonstrated for the synthesis of azepinoindoles in good to excellent yields in one-pot. First, rhodium-catalyzed [2 + 1] cycloaddition reaction smoothly took place to produce iminyl vinyl cyclopropane intermediate at room temperature in chlorobenzene for 1 h, which was thermally converted to azepinoindoles via aza-Cope rearrangement.

Construction of Indole‐Fused Heterocycles Starting from 2‐Thioxoindolines, Iminoindolines, and Their Derivatives

“…The desired azepinoindoles 43 were obtained in good-to-excellent yields (up to 98% yield) (Scheme 15c). [22] In 2018, Wang and co-workers reported a rhodiumcatalyzed [5 + 3] cycloaddition reaction between 3diazoindolin-2-imines 21 and cyclic thioester 49 to synthesize a series of 7,8-dihydrobenzo [7,8][1,4] thiazocino[3,2-b]indol-6(5H)-ones 50. 3-Diazoindolin-2imines 21 with electron-withdrawing or electrondonating substituents on aromatic ring reacted smoothly to afford the corresponding products 50 in good yields (Scheme 16).…”

Recent Achievements in the Rhodium‐Catalyzed Concise Construction of Medium N‐Heterocycles, Azepines and Azocines

“…This transformation proceeded via sequential cyclopropanation of metal carbenoids with dienes, followed by aza-Cope arrangemet. [18] Lee group also developed a azepinoindoles synthesis via rhodium-catalyzed formal [4 + 3] cycloaddition between 3-diazoindolin-2-imines and 1,3dienes, featuring good functional group tolerance, short reaction time. Notably, no silver salt was used in this transformation.…”

“…Similar to Beier's work, when hydrolyzale OTMS‐ substituents were used, azepino [2,3‐ b ] indol‐4(1 H )‐ones were obtained (Scheme 22). This transformation proceeded via sequential cyclopropanation of metal carbenoids with dienes, followed by aza‐Cope arrangemet [18] …”

Highly Regio‐, Diastereo‐, and Enantioselective Assembly of Azepino[2,3‐b]indoles viaPalladium‐Catalyzed [4 + 3] Cycloaddition†

“…[2] In this context, several synthetic methods for achiral or racemic azepino [2,3-b]indoles were reported. [3] In particular, Li and coworkers developed an elegant [4 + 3] annulation of indoline-based aza-dienes with sulfur ylides to construct azepino- [2,3-b]indoles. [3c] However, only moderate enantioselectivity (64% ee) for a single example was obtained by using a chiral sulfide catalyst.…”