Rhodium-Catalyzed C(sp²)–H Alkoxycarbonylation/Acylation of Indolines with Anhydrides as a Carbonyl Source

Abstract

We developed rhodium-catalyzed alkoxylcarbonylation/acylation of indolines using anhydrides as a safe and easy-to-handle carbonyl source. This catalytic process represents an additive- and CO-free carbonylation, establishing a simple and straightforward protocol for synthesizing C7-carbonylated indolines. Notably, this reaction provides a successful example of C–H acylation of indolines that results in the formation of α-branched ketones, which were difficult to prepare by previously reported analogous catalytic reactions.

Rhodium-catalysed decarbonylative C(sp2)–H alkylation of indolines with alkyl carboxylic acids and carboxylic anhydrides under redox-neutral conditions

“…Based on the aforementioned experimental results and previous reports, 13,14,16 we propose the reaction mechanism depicted in Fig. 1.…”

“…Considering these limitations, we developed the redox-neutral decarbonylative alkylation of indolines by employing ( in situ -formed) carboxylic anhydrides (Scheme 1c). 16…”

Transition metal-catalyzed regioselective functionalization of carbazoles and indolines with maleimides

“…Based on our control experiments and the reported literature, 16–18,20–23 the mechanistic pathways for the formation of 3a and 6a were proposed, as outlined in Schemes 7 and 8, respectively. Initially, active Ru( ii ) complex A generated from [Ru( p -cymene)Cl 2 ] 2 , AgSbF 6 , and Cu(OAc) 2 ·H 2 O reacts with 1a to give 6-membered ruthenacycle B via C–H activation at the C-1 position.…”

“…Initially, active Ru( ii ) complex A generated from [Ru( p -cymene)Cl 2 ] 2 , AgSbF 6 , and Cu(OAc) 2 ·H 2 O reacts with 1a to give 6-membered ruthenacycle B via C–H activation at the C-1 position. 16–18 The coordination of 2a with intermediate B gives intermediate C , which undergoes a migratory insertion of the maleimide unit to produce eight-membered ruthenacycle D . Intermediate D then affords the final product 3a via protodemetalation in an acidic medium, and regenerates active catalyst A for use in further catalytic cycles.…”

“…12 Owing to this importance, a number of strategies for the functionalization of carbazoles and indolines have been developed based on C–H activation protocols. 13 These methods include the transition metal-catalyzed C–H functionalization of carbazoles at the C-1 position and indolines at the C-7 position bearing directing groups with coupling partners for the introduction of alkyl, 14 alkenyl, 15 alkynyl, 16 aryl, 17 acyl, 18 alkoxycarbonyl, 19 amino, 20 amide, 21 arylthio, 22 nitro, 23 cyano, 24 and halide 25 groups (Scheme 1A). Additionally, some important studies on C–H functionalization involving maleimides have also been reported.…”