Ruthenium-Catalyzed Electrochemical Synthesis of Indolines through Dehydrogenative [3 + 2] Annulation with H₂ Evolution

Abstract

A dehydrogenative [3 + 2] annulation reaction of aniline derivatives and alkenes has been developed via the ruthenium-electron catalytic systems for the synthesis of versatile indolines. Electricity is used as a sustainable oxidant to regenerate the active Ru­(II) catalyst and promote H2 evolution. This protocol is ecofriendly and easy to handle as it uses a simple undivided cell in mild conditions without the employment of metal oxidants.

Electro-organic synthesis: an environmentally benign alternative for heterocycle synthesis

“…product along with the formation of Ru-VII complex, which is re-oxidised anodically (Scheme 69). Shen et al 145 reported the synthesis of indolines (196) via dehydrogenative [3+2] annulation of aniline derivatives with terminal alkene in the presence of Ru(II) metal catalyst. In order to find the most efficient reaction conditions, the initial pre-screening of the reaction was performed using N-2-pyrimidyl-substituted aniline (195b) and styrene (31a) as model substrates.…”

Scalable Rhodaelectro-Catalyzed Expedient Access to Seven-Membered Azepino[3,2,1- hi ]indoles via [5 + 2] C–H/N–H Annulation

“…Increasing or decreasing the amount of Li 2 CO 3 also reduced the yield (entries [11][12]. Control experiments verified the crucial role of Li 2 CO 3 , rhodium catalysts and electricity (entries [13][14][15]. Three other typical transition metals were also explored, but no target products were obtained (entries [16][17][18].…”

Rh(III)-Catalyzed [3 + 2] Annulation of Aniline Derivatives with Vinylsilanes via C–H Activation/Alkene Cyclization: Access to Highly Regioselective Indoline Derivatives

“…A catalytic cycle is proposed based on the experimental results obtained and previous reports (Scheme ). ,,, The active catalyst C is generated from [Cp*RhCl 2 ] 2 in the presence of AgSbF 6 , Ag 2 CO 3 , and 1a through the directed ortho-rhodation . The coordination of an alkene to the rhodium complex C forms complex E′ , which undergoes the migratory insertion of an alkene into a Rh–C bond to generates the eight-membered Rh complex E .…”

“…In contrast, the use of a metal-catalyzed C–H activation/alkene cyclization cascade to construct indoline frameworks has been less explored because the intermediate A is prone to undergo β-hydride elimination, which then leads to the formation of alkenylated products (Scheme a) . To overcome these limitations, various strategies have been developed to retard the β-hydride elimination and various C–H activation/alkene cyclization reactions, leading to the production of indoline derivatives. − However, all of the examples reported thus far exclusively lead to the production of C2-substituted indolines, and only activated alkenes, such as 1,3-dienes, norbornene, vinylnaphthalene, acrylic esters, styrenes, ,, and allyl acetates can be used as an alkene partner. To the best of our knowledge, there are no reported examples of the selective production of C3-substituted indolines via C–H activation/alkene cyclization (Scheme b). …”