Copper‐Catalyzed Aerobic Cross‐Dehydrogenative Coupling of β‐Oxime Ether Furan with Indole

Abstract

Heterobiaryls serve as relevant structural motifs in many fields of high applicative importance such as drugs, agrochemicals, organic functional materials etc. Cross-dehydrogenative coupling involving direct oxidation of two CÀ H bonds to construct a CÀ C bond is actively being pursued as a more benign and 'greener' alternative for synthesizing heterobiaryls. Herein, we report a Cu(I)-catalyzed crossdehydrogenative coupling of indoles and furans, two of the most important aromatic heterocycles using air as the terminal oxidant. The reaction proceeds with regio-and chemoselectivity to give the cross-coupled products in good to excellent yields generally. A broad substrate scope with respect to both the coupling partners has been demonstrated to prove the generality of this reaction. This represents the hitherto unexplored cross-dehydrogenative coupling methodology to obtain an indole-furan biaryl motif.

Recent Advances in Aerobic Oxidative of C−H Bond by Molecular Oxygen Focus on Heterocycles

“…Narayan reported a cross dehydrogenation coupling of substituted indoles ( 90 ) and furans ( 89 ) catalyzed by Cu(I), using air as the terminal oxidant, a series of diaryl motifs ( 91 ) were obtained with moderate to good yields (Scheme 19). [39] Further research indicates that the oxime ether group in furan acts as an activating group, making it essential for this reaction.…”

Cu(ii)-catalyzed aerobic oxidative coupling of furans with indoles enables expeditious synthesis of indolyl–furans with blue fluorescence

“…As a proof-of-concept, we recently reported our initial findings where Cu( i )/air combination was able to catalyze the direct coupling of a limited set of ‘oxime-ether activated’ furans with indoles ( Scheme 1d ). 12 However, all the cross-coupled products had oxime ether as a redundant substituent which severely limited the scope of the reaction.…”

Cationic palladium(ii)-catalyzed synthesis of substituted pyridines from α,β-unsaturated oxime ethers

“…8,9 However, with regard to α,β-unsaturated oximes, there are only a few reports on extension of this electron-donating ability to conjugated olefins. 10 Because of the electron-donating effect of an electron lone pair, conjugated systems of α,β-unsaturated oximes, especially at the β-position, can potentially exhibit nucleophilic reactivity (Fig. 1).…”