Rhodium‐Catalyzed Cyclization of Diynes with Nitrones: A Formal [2+2+5] Approach to Bridged Eight‐Membered Heterocycles

Wang, Chunxiang; Wang, Dongping; Hao, Yan; Wang, Haolong; Pan, Bin; Xin, Xiaoyi; Li, Xincheng; Wu, Fan; Wan, Boshun

doi:10.1002/anie.201407394

Cited by 56 publications

(33 citation statements)

References 55 publications

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“…Thep referential formation of 3r,h aving an electron-rich substituent, implies that the slow hydrogen abstraction might occur after the electrophilic attack of palladium(II) on the aromatic ring in the CÀHa ctivation process. [18] Moreover, reacting the palladacycle complex 4,w hich was generated from 1a by palladium(II)-mediated CÀHb ond cleavage, [15a] with an equal molar amount of 2a successfully led to 3a in 93 %y ield (Scheme 2c), thus providing solid evidence to support afree-amine-directed C À Hactivation mechanism for the title transformation. Finally,t wo control reactions were performed, and the experimental data revealed that 3a was not formed from 5 by ap ossible amination/oxidation sequence (Scheme 2d), [16a] but generated through the tautomerization of its enamine-counterpart 6 (Scheme 2e).…”

Section: Methodsmentioning

confidence: 96%

Highly Stereoselective Synthesis of Imine‐Containing Dibenzo[b,d]azepines by a Palladium(II)‐Catalyzed [5+2] Oxidative Annulation of o‐Arylanilines with Alkynes

et al. 2015

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An ovel palladium(II)-catalyzed [5+ +2] oxidative annulation of readily available o-arylanilines with alkynes has been developed for building aseven-membered N-heterocyclic architecture containing ab iaryl linkage.T his method is applicable to aw ide range of unprotected o-arylanilines and internal alkynes,and results in the chemoselective preparation of imine-containing dibenzo [b,d]azepines in high yields with excellent diastereoselectivity with respect to the two types of stereogenic elements.Dibenzo [b,d]azepines represent an important class of medium-sized N-heterocycles because they are the key structural motifs in many natural products and bioactive compounds ( Figure 1). Forexample,dimeric erythrivarine B, which contains the seven-membered skeleton, was isolated from cultivated E. variegata.[1] LY-411575 was identified as an effective g-secretase inhibitor for the treatment of melanoma and Alzheimers disease. [2] Functionalized dibenzo [b,d]azepines were also investigated as serotonin (5-HT) receptor [3] and potassium channel inhibitor.[4] Therefore, the search for new reliable synthetic approaches for the preparation of dibenzo [b,d]azepines from readily available starting materials is of great interest.Recently,t ransition-metal-catalyzed C À Hf unctionalization has emerged as an efficient and versatile method for accessing various heterocycles and carbocycles.[5] In particular, nitrogen-group-assisted heteroannulations of nitrogencontaining coupling partners with alkynes by aC À Hcleavage/ alkyne insertion/cyclization cascade have been widely used to generate structurally diverse N-heterocyclic compounds,such as indoles, [6] pyrroles, [7] isoquinolines, [8] isoquinolinones, [9] and so on.[10] Remarkably,m ost of these transformations were realized by formal [3+ +2] or [4+ +2] cycloadditions to give fiveor six-membered rings,but the construction of larger rings by means of related annulations is quite rare. [10c,e] In this context, we set out to develop anew type of [5+ +2] annulation between simple biaryl precursors and alkynes involving aC À H activation step for the synthesis of functionalized dibenzo-[b,d]azepines. [11] This work originated from our recent studies on ruthenium(II)-catalyzed oxidative annulation of o-arylphenol derivatives with alkynes through aC À Ha ctivation strategy (Scheme 1a).[12] It is noteworthy that the reaction proceeded exclusively by ad earomatizing [3+ +2] annulation pathway to generate spirocyclic enones as the sole product, but not dibenzoxepines through apossible [5+ +2] cycloaddition route. Presumably,aclear steric clash between the two twisted aromatic groups of the intermediate A played ak ey role in driving the essential ring contraction from A to B,t hus hampering the reductive elimination of A to form adibenzoxepine and rendering the [3+ +2] spiroannulation more favorable than as even-membered ring formation. Moreover, ar ecent seminal report from the group of MascareÇas and Gulías demonstrated that simple o-vinylphenols (R = H), which cannot enga...

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Section: Methodsmentioning

confidence: 96%

Highly Stereoselective Synthesis of Imine‐Containing Dibenzo[b,d]azepines by a Palladium(II)‐Catalyzed [5+2] Oxidative Annulation of o‐Arylanilines with Alkynes

et al. 2015

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“…In 2013 we reported the first catalytic C−H activation of nitrones . Later, we and others realized their couplings with alkenes, alkynes, diazo compounds, and arenes under redox‐neutral conditions, where the role of the nitrone is limited to its oxidizing or electrophilic properties in post‐coupling transformations –. Of note, although nitrones are typical 1,3‐dipoles, integration of both C−H activation and dipolar addition has not been realized and these two areas evolved separately.…”

Section: Methodsmentioning

confidence: 99%

Nitrone Directing Groups in Rhodium(III)‐Catalyzed C−H Activation of Arenes: 1,3‐Dipoles versus Traceless Directing Groups

Xie

et al. 2016

Angewandte Chemie

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Functionalizable directing groups (DGs) are highly desirable in C À Ha ctivation chemistry.T he nitrone DGs are explored in rhodium(III)-catalyzed CÀHa ctivation of arenes and couplings with cyclopropenones.N -tert-butyl nitrones bearing as mall ortho substituent coupled to afford1 -naphthols,w here the nitrone acts as at raceless DG.I nc ontrast, coupling of N-tert-butyl nitrones bearing ab ulkyortho group follows aC À Ha cylation/[3+ +2] dipolar addition pathway to give bicyclics.The coupling of N-arylnitrones follows the same acylation/[3+ +2] addition process but delivers different bicyclics.

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“…Meanwhile, the same group used diazo compounds instead of alkynes coupling partners to give access to N-hydroxyindolines under a similar catalytic system [64]. Nitrones as redox-neutral directing group are broadly applied in transition-metal-catalyzed C-H activation/coupling with π-system [61,62]. In 2015, Chang and co-workers developed a Rh(III)catalyzed coupling reaction between arylnitrones and alkynes without the requirement for external oxidant, where Rhodium catalyst not only operates in the C−H bond activation but also evolve Oatom transfer process.…”

Section: Indole Derivativesmentioning

confidence: 99%

Rh(III)-Catalyzed C–H Bond Activation for the Construction of Heterocycles with sp3-Carbon Centers

et al. 2019

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Rh(III)-catalyzed C–H activation features mild reaction conditions, good functional group tolerance, high reaction efficiency, and regioselectivity. Recently, it has attracted tremendous attention and has been employed to synthesize various heterocycles, such as indoles, isoquinolines, isoquinolones, pyrroles, pyridines, and polyheterocycles, which are important privileged structures in biological molecules, natural products, and agrochemicals. In this short review, we attempt to present an overview of recent advances in Rh(III)-mediated C–H bond activation to generate diverse heterocyclic scaffolds with sp3 carbon centers.

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Rhodium‐Catalyzed Cyclization of Diynes with Nitrones: A Formal [2+2+5] Approach to Bridged Eight‐Membered Heterocycles

Cited by 56 publications

References 55 publications

Highly Stereoselective Synthesis of Imine‐Containing Dibenzo[b,d]azepines by a Palladium(II)‐Catalyzed [5+2] Oxidative Annulation of o‐Arylanilines with Alkynes

Highly Stereoselective Synthesis of Imine‐Containing Dibenzo[b,d]azepines by a Palladium(II)‐Catalyzed [5+2] Oxidative Annulation of o‐Arylanilines with Alkynes

Nitrone Directing Groups in Rhodium(III)‐Catalyzed C−H Activation of Arenes: 1,3‐Dipoles versus Traceless Directing Groups

Rh(III)-Catalyzed C–H Bond Activation for the Construction of Heterocycles with sp3-Carbon Centers

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