Reductive dearomative arylcarboxylation of indoles with CO2 via visible-light photoredox catalysis

Abstract

Catalytic reductive coupling of two electrophiles and one unsaturated bond represents an economic and efficient way to construct complex skeletons, which is dominated by transitionmetal catalysis via two electron transfer. Herein, we report a strategy of visible-light photoredox-catalyzed successive single electron transfer, realizing dearomative arylcarboxylation of indoles with CO 2. This strategy avoids common side reactions in transition-metal catalysis, including ipso-carboxylation of aryl halides and β-hydride elimination. This visible-light photoredox catalysis shows high chemoselectivity, low loading of photocatalyst, mild reaction conditions (room temperature, 1 atm) and good functional group tolerance, providing great potential for the synthesis of valuable but difficultly accessible indoline-3-carboxylic acids. Mechanistic studies indicate that the benzylic radicals and anions might be generated as the key intermediates, thus providing a direction for reductive couplings with other electrophiles, including D 2 O and aldehyde.

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

“…Notably, during our investigation, the Yu group reported the 2,3-arylcarboxylation of indoles, a class of well-studied electron-rich heteroarene in dearomatization reactions, via 5-exo-trig cyclization (Scheme 1b). 90 Surprisingly, a chemoselective dearomatization of non-activated phenyl ring via 6-exo-trig cyclization occurred with 2-phenyl indoles substates under our reaction conditions, leading to products that were distinct from those of Yu's work (Scheme 1c). In line with our continuous interest in catalytic utilization of CO2, 91,92 which is an abundant, lowcost, sustainable and nontoxic C1 building block, herein, we report a spirocyclizative remote arylcarboxylation of arenes with CO2 by visible-light-induced reductive dearomatization of aromatics bearing naphthalenyl, phenyl, and quinolinyl groups via RPCC, providing a rapid access to valuable complex three-dimensional frameworks (Scheme 1c).…”

“…During the study, we also obtained surprisingly unexpected reactivity with 2-phenyl indoles (Scheme 5). Interestingly, dearomatization occurred predominantly at non-activated phenyl ring via 6-exo-trig cyclization rather than at the activated indole ring's C2-C3 double bond via 5-exo-trig in previous study with the same substrate, 90 leading to spirocyclic product 55 with a formal remote C-H carboxylation. [96][97][98] The rationale for this chemoselectivity is not clear at present.…”

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

“…Interestingly, dearomatization occurred predominantly at non-activated phenyl ring via 6-exo-trig cyclization rather than at the activated indole ring's C2-C3 double bond via 5-exo-trig in previous study with the same substrate, 92 leading to spirocyclic product 55 with a formal remote C-H carboxylation. [98][99][100] The rationale for this chemoselectivity is not clear at present.…”

Visible Light‐Mediated Construction of Sulfonated Dibenzazepines

“…However, the strong base Cs 2 CO 3 mediated nucleophilic aromatic substitution reaction (S N Ar) under microwave irradiation was failed and a very fast decomposition of 4-3 or 1'-2 was observed, which could be attributed to the instability of the dipeptide structure under strong bases and high temperature. [15] With this in mind, we intended to try to synthesize compound 6 through visible lightmediated cascade radical 1,5-H shift process and base-promoted homolytic aromatic substitution (BHAS) reaction of 4-4 or 4-5, [16] unfortunately, no desired product was obtained (see Supporting Information). In order to expand the scope of the radical cyclization protocol, alkyl sulfonyl chlorides were examined under standard conditions, delightly, desired product 8 was formed when i-PrSO 2 Cl was used instead of aryl sulfonyl chlorides.…”