The rhodium(III)-catalyzed C-H functionalization followed by intramolecular annulation reactions between azobenzenes and sulfoxonium ylides is described. This protocol leads to the efficient formation of 3-acyl (2 H)-indazoles with a range of substrate scope. A high level of chemoselectivity and functional group tolerance of this transformation were also observed.
The transient directing group promoted C(sp)-H functionalization of benzaldehydes with anthranils by a cationic rhodium(III) catalyst is described. Notably, anthranils have been used as both transient directing groups and amination sources to afford 2-acyl acridines through direct C-H amination followed by acid-mediated cyclization. A range of substrate scopes and functional group tolerance were observed.
The rhodium(III)-catalyzed cross-coupling reaction between commercially available benzylamines and Morita–Baylis–Hillman (MBH) adducts is described. This protocol provides a facile access to various 2-benzazepine derivatives via the C(sp2)–H activation of N-allylated benzylamines and subsequent intramolecular olefin insertion followed by N-allylation reaction. A range of substrates has been used, and a high level of chemoselectivity as well as functional group tolerance was observed. To gain mechanistic insight of this transformation, DFT calculations were also performed.
The ruthenium(II)-catalyzed C À Hfunctionalization of (hetero)aryl azomethine imines with allylic acetals is described.The initial formation of allylidene-(methyl)oxoniums from allylic acetals could trigger C(sp 2 )À Ha llylation, and subsequent endo-type [3+ +2] dipolar cycloaddition of polar azomethine fragments to deliver valuable indenopyrazolopyrazolones.T he utility of this method is showcased by the late-stage functionalization of bioactive molecules such as estrone and celecoxib.C ombined experimental and computational investigations elucidate ap lausible mechanism of this new tandem reaction. Notably,the reductive transformation of synthesized compounds into biologically relevant diazocine frameworks highlights the importance of the developed methodology.Inrecent decades,g reat advances in transition-metal-catalyzed CÀHf unctionalization have been achieved due to its remarkable advantage in atom economy and environmental sustainability. [1] Thec ombination of C À Hf unctionalization and annulation with various p-unsaturated reactants has been recognized as avaluable strategy for the efficient construction of carbocyclic and heterocyclicc ompounds. [2] Significant progress in this direction has been realized by av ariety of transition-metal catalysts.I np articular, ruthenium catalysts have been employed due to their low cost, high efficiency, broad substrate scope,a nd good functional group tolerance under relatively mild conditions. [3] Azomethine imines have been widely employed in cycloaddition reactions with various coupling partners such as alkenes,a lkynes,a nd allenoates. [4] Recently,L ie tal. has reported the C(sp 2 ) À Hf unctionalization of azomethine imines under Rh III catalysis to provide 1,2-dihydrophthalazi-nes [5a] and bridged benzoxazepines. [5b] Alkenes have been intensively studied for the formation of heterocyclic compounds in CÀHf unctionalization event involving the nucleophilic addition of directing groups to olefinic moieties or the electrophilic addition of directing groups to M À Ci ntermediates.V ery recently,our group disclosed the Rh III -catalyzed C À Hf unctionalization and in situ annulation reaction using Morita-Baylis-Hillman adducts to afford 2-benzazepines, [6a] bridged benzoxazepines, [6b] and 2-naphthols. [6c] In these transformations,weobserved that the ester functionality on MBH adducts can lower the energy barrier of the migratory insertion step,h ence enhancing the catalytic cycle.O nt he other hand, allyl acetate was inactive under the identical reaction condition, which was supported by DFT calculations. [6a] These results indicate that the electron density on olefin moiety is crucial for the success of the reaction. In this regard, we envisioned that we might overcome this issue if ah igher inductive effect at the allylic position can be produced. Owing to their equilibrium under metal catalysis, [7] allylic acetals might serve as highly activated acrolein oxonium precursors for cross-coupling reactions (Scheme 1A). Interestingly,w ed iscovered in the...
Rhodium(III)-catalyzed hydroxymethylation followed by intramolecular annulation of azobenzenes using paraformaldehyde as a valuable C1-feedstock is described. The method is readily extended to the coupling reaction between azobenzenes and trifluoroacetaldehyde. This transformation efficiently produces a range of C3-unsubstituted and C3-trifluoromethylated (2H)-indazoles, which are important targets in the development of novel bioactive compounds. Excellent chemoselectivity and functional group tolerance were observed. The synthetic transformation of C3-unsubstituted (2H)-indazoles highlights the utility of the developed method.
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