Rhodium(iii)-catalyzed successive C(sp²)–H and C(sp²)–C(sp²) bond activation of aryl oximes: synthetic and mechanistic studies

Abstract

Merging selective C–H cleavage with C–C cleavage in a tandem reaction has been a practical strategy that permits skeletal diversification from simple raw materials. Herein, we describe a rhodiumIII-catalyzed redox-neutral...

Rhodium(III)‐Catalyzed Redox‐Neutral Synthesis of Indenones from 2‐Aryl‐3‐nitrosoindoles with Alkynes

“…The isotope labeling experiments and detection of by-product 2-aminobenzonitrile implied hydrolysis of an imine cation, that was most likely generated from spirocyclicindoline 3 aa-oxime via NÀ O and CÀ C bond cleavage according to our previous works (Scheme 2f). [19,20] To obtain the detailed pathway on the formation of the above-mentioned spirocyclic intermediate, the density functional theory (DFT) calculation was performed. The reaction of indole 1 a with alkyne 2 a at 363.15 K was discussed (Figure 1).…”

“…Mechanistic studies supported the formation of intermediates N-H-spiroindoline-3-one oximes via alkenylation and C=N addition, which were reactive to undergo NÀ O and CÀ C bond cleavage to give the final nitrile-containing products (Scheme 1i). [19] More recently, we reported a dearomative spirocyclization using another type of nitrosated 2-arylindoles, namely 2-aryl-1-methyl-3-nitrosoindoles. Different from our earlier report, this reaction proceeded smoothly via alkenylation and dearomatization under very mild conditions and relied on the use of specific alkynes, i. e. phenyl alkyl alkynes and 1,3-diynes (Scheme 1j).…”

Rhodium(iii)-catalyzed mild and regioselective dearomative spirocyclization of 2-aryl-3-nitrosoindoles with alkynes

“…2-Aryl-1-methyl-3-nitrosoindoles are easily prepared nitrosation derivatives from 2-arylindoles (Scheme 1, right-down figure). As a continuation of the research on the C–H cyclization of nitrosated 2-arylindoles with alkynes, 13 we propose the mild and redox-neutral dearomative spirocyclization of 2-aryl-1-methyl-3-nitrosoindoles with unsymmetrical alkynes in satisfactory regioselectivity and 100% atom-economy (Scheme 1g).…”