Gadolinium Photocatalysis: Dearomative [2+2] Cycloaddition/Ring‐Expansion Sequence with Indoles

Abstract

Lanthanide photocatalysts are muchless investigated in synthetic chemistry than rare and expensive late transition metals.W eh erein introduce Gd III photocatalysis of ah ighly regioselective,i ntermolecular [2+ +2] photocycloaddition/ringexpansion sequence with indoles,w hich could provide divergent access to cyclopenta[b]indoles and indolines.Asimple and commercially available Gd(OTf) 3 salt is sufficient for this visible-violet-light-induced transformation. The reaction proceeds either through atransient or start-to-end dearomatization cascade and shows excellent regioselectivity (usually > 95:5 r.r.), broad scope (59 examples), good functional group tolerance and facile scale-up under mild, direct visible-lightexcitation conditions.M echanistic investigations reveal that direct excitation of the Gd(OTf) 3 /indole mixture gives an excited state intermediate,w hich undergoes the subsequent [2+ +2] cycloaddition and cyclobutane-expansion cascade. Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Spirocyclizative Remote Arylcarboxylation of Non-Activated Arenes with CO2 via Visible-Light-Induced Reductive Dearomatization

“…We suspected the product might be labile, resulting in a relatively lower yield. Gratifyingly, substrates bearing a series of substituents on the indole ring or the aryl bromide ring could be converted into the corresponding products in moderate yields (56)(57)(58)(59)(60)(61)(62)(63)(64)(65). It should be mentioned, generally about 5% of arylcarboxylation of indole's C2-C3 double bond and/or about 5% of direct debromination side products were also observed.…”

“…In recent years, visible-light photoredox catalysis [35][36][37][38][39][40][41][42][43][44] has emerged as a promising strategy for developing mild protocols for dearomatization, [45][46][47][48][49][50][51][52][53][54][55][56][57][58] including several significant protocols for the dearomatization of nonactivated arenes, [59][60][61][62][63][64][65][66][67][68][69][70][71][72][73] such as dearomative cycloadditions mainly from the groups of Sarlah and Bach, [59][60][61][62] and oxidative dearomatization. [63][64][65] A distinct redox-neutral hydroalkylative dearomatization of naphthalene derivatives was also reported by the group of Zhang, Mei and You.…”

Spirocyclizative Remote Arylcarboxylation of Nonactivated Arenes with CO 2 via Visible-Light-Induced Reductive Dearomatization

“…We suspected the product might be labile, resulting in a relatively lower yield. Gratifyingly, substrates bearing a series of substituents on the indole ring or the aryl bromide ring could be converted into the corresponding products in moderate yields (56)(57)(58)(59)(60)(61)(62)(63)(64)(65). It should be mentioned that generally about 5% product of arylcarboxylation of indole's C2-C3 double bond, and side products from debromination (about 5%) as well as hydroarylation of the 2-phenyl group (generally less than 5%) were also observed.…”

“…In recent years, visible-light photoredox catalysis [36][37][38][39][40][41][42][43][44][45] has emerged as a promising strategy for developing mild protocols for dearomatization, [46][47][48][49][50][51][52][53][54][55][56][57][58][59] including several significant protocols for the dearomatization of nonactivated arenes, [60][61][62][63][64][65][66][67][68][69][70][71][72][73][74] such as dearomative cycloadditions that were mainly from the groups of Sarlah and Bach, [60][61][62][63] and oxidative dearomatization. [64][65][66] A distinct redox-neutral hydroalkylative dearomatization of naphthalene derivatives was also reported by the group of Zhang, Mei and You.…”

Organophotocatalytic dearomatization of indoles, pyrroles and benzo(thio)furans via a Giese-type transformation

“…Single-electron transfer (SET) involved oxidation-induced C-H functionalization of the nucleophilic indoles has been elegantly realized as powerful alternatives for indole dearomatization 17 , particularly mild, green visible light photocatalytic and electrochemical methods (Fig. 1a) 3,15,[18][19][20][21][22][23][24][25][26][27][28][29] .…”