Palladium/Norbornene‐Catalyzed C−H Alkylation/Alkyne Insertion/Indole Dearomatization Domino Reaction: Assembly of Spiroindolenine‐Containing Pentacyclic Frameworks

Abstract

Reported is ah ighly chemoselective intermolecular annulation of indole-based biaryls with bromoalkyl alkynes by using palladium/norbornene (Pd/NBE) cooperative catalysis. This reaction is realized through as equence of Catellani-type C À Halkylation, alkyne insertion, and indole dearomatization, by forming two C(sp 2 ) À C(sp 3 )and one C(sp 2 ) À C(sp 2 )bonds in asingle chemical operation, thus providing adiverse range of pentacyclic molecules,c ontaining as piroindolenine fragment, in good yields with excellent functional-group tolerance. Preliminary mechanistic studies reveal that CÀHb ond cleavage is likely involved in the rate-determining step,a nd the indole dearomatization might take place through an olefin coordination/insertion and b-hydride elimination Heck-type pathway. Scheme 1. Proposalf or an ew [Pd 0 ]/NBE-catalyzed reaction sequence which terminates with indole dearomatization.

Electrooxidation enables highly regioselective dearomative annulation of indole and benzofuran derivatives

“…Over the past several decades, dearomative annulation of indoles has served as one of the most popular avenues for preparing polycyclic indoline skelotons [12][13][14][15] . Some powerful protocols like cyclopropanation 16,17 , 1,3-dipolar cycloadditions 18 , [2+ 2] photo-cycloadditions 19 , Diels-Alder [20][21][22] , and cascade electrophilic addition/annulation reactions [23][24][25][26] have been well established. In these cases, most of the strategies took advantage of the C2-C3 π bond or the inherent strong nucleophilicity of C3 position, and had the advantage of rapid construction for highly functionalized indoline frameworks in one step.…”

Catellani Reaction: An Enabling Technology for Vicinal Functionalization of Aryl Halides by Palladium(0)/Norbornene Cooperative Catalysis

“…[40] Scheme 12 ortho-Alkylation of aryl iodides followed by alkyne insertion In 2018, Luan and co-workers reported a highly chemoselective Pd/NBE-catalyzed spiroannulation reaction of indole-based biaryls with bromoalkyl alkynes (Scheme 13). [41][42] This domino process was first initiated by the ortho C-H alkylation, which was followed by migratory insertion of alkyne and subsequent dearomatization of indole fragment, thus affording a wide range of pentacyclic molecules (29). Noteworthy, the distinct feature of this reaction is the termination of such a domino process through the indole dearomatization.…”

Trifunctionalization of Aryl Iodides with Two Distinct Nitrogen and Carbon Electrophiles by Palladium/Norbornene Catalysis

“…If so, it would lead to highly valuable 1,2,3‐trifunctionalized arenes by the direct trifunctionalization of ortho ‐unsubstituted aryl halides at their three adjacent positions. [ 34‐38 ] However, the development of such a reaction is not a trivial task. According to the reactivity difference of electrophiles E a and E b that are involved, two main reaction modes could be envisioned.…”