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

Abstract

Herein, we develop a Rh(III)-catalyzed intermolecular regioselective dearomative spirocyclization of 2-aryl-3-nitrosoindoles with alkynes, featuring the redox-neutral and atom-economy construction of spiroindoline-3-one oximes bearing a C2 spirocyclic quaternary carbon center under...

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

“…When 18 O‐labeled water was added to the model reaction, indenones containing 18 O‐ and 16 O‐atom were afforded in high yield, which indicated that the hydrolysis is involved in the formation of indenone (Scheme 2e). 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 N−O and C−C bond cleavage according to our previous works (Scheme 2f) [19,20] …”

“…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).…”

“…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). [20] When other alkynes such as diarylalkynes and phenyl acyl alkynes were used, higher temperature was necessary and therefore the spirocyclic product further underwent N À O and C À C bond cleavage and hydrolysis. As an extension of our previous work, we herein report the reaction of 2-aryl-1-methyl-3-nitrosoindoles with alkynes to generate indenones and 2-aminobenzonitriles (Scheme 1k).…”

C–H activation-initiated spiroannulation reactions and their applications in the synthesis of spirocyclic compounds

“…The 1,3-diynes also took part in the reaction to afford alkyne-containing C2-spiroindolines (Scheme 11). 11…”