Organocatalytic C(sp³)–H Functionalization via Carbocation-Initiated Cascade [1,5]-Hydride Transfer/Cyclization: Synthesis of Dihydrodibenzo[b,e]azepines

Abstract

Carbocation-initiated cascade [1,5]-hydride transfer/cyclization and dimerization reactions were developed to synthesize dihydrodibenzo[b,e]azepine and octahydrodipyrroloquinoline derivatives in high yields. These redox-neutral C(sp)-H functionalization-involving cascade reactions feature transition-metal-free, high atom- and step-economy, and environmental friendliness with water as the sole byproduct.

The Cascade [1,5]-Hydride Shift/Intramolecular C(sp3)–H Activation: A Powerful Approach to the Construction of Spiro-Tetrahydroquinoline Skeleton

“…(2) The current application of the cascade [1,5]-hydride shift/cyclization strategy mainly focuses on the construction of five- and six-membered spiro-tetrahydroquinoline. However, exploration of building a spiro-architecture with a challenging ring size (like divergent synthesis of medium ring size) as well as conducting total synthesis of a structurally complex natural product remain elusive ( Li et al, 2018b ; Wang et al, 2018 ; Kataoka et al, 2019 ; Hu et al, 2020 ; Shen et al, 2020 ; Hu et al, 2021a ; Hu et al, 2021b ; Wang et al, 2021 ; Yang S. et al, 2021 ). (3) Notably, the application of [1,5]-hydride shift/cyclization strategy in stereoselective chemistry was barely reported ( Mori et al, 2018 ).…”

Toward the synthesis of incargranine B and seneciobipyrrolidine. Synthesis of octahydro‐dipyrroloquinoline skeleton via dipolar cycloaddition/amination sequence

“…Finally, Li group reported application of Cu(OTf) 2 in the dimerization of same type of starting materials, N‐phenylhomopropargyl amines, and applied it in the synthesis of both alkaloids [6]. Many other approaches to the synthesis of the core structure have been reported in the literature, but essentially they are based on the oxidative transformations of N‐phenylpyrrolidines or the cyclative processes of N‐phenylhomopropargyl amines [7–19]. Of other methods, perhaps, notable are those based on intramolecular dipolar cycloaddition reactions of azomethine ylides which have been explored in the synthesis of martinelline [20–31].…”

1,5-Hydride-Shift-Triggered Cyclization for the Synthesis of Unsymmetric Julolidines

“…[9][10][11][12][13][14] Such reactions allow tetrahydroquinoline derivatives to be obtained in a straightforward and redox-neutral manner (Scheme 1, previous work). 15 Significant progress in this area is associated with Lewis acid (LA) catalysis, 12,15 especially with the enantioselective procedure developed by Seidel's group, 16 which has allowed various applications involving alternative hydride acceptors [17][18][19][20][21][22][23][24][25] as well as the use of donating groups with shorter or longer tethers. [26][27][28][29][30] Assembly of julolidines via a 1,5-hydride-shift-triggered cyclization could be of benefit due to the unambiguous regioselectivity of hydride transfer and the straightforward access to unsymmetrically substituted derivatives 1 (Scheme 1, this work).…”