Site-selective Suzuki cross-coupling reactions of 2,3-dibromobenzofuran

Rapid regio- and multi-coupling reactivity of 2,3-dibromobenzofurans with atom-economic triarylbismuths under palladium catalysis

“…This reflects the efficient nature of our established pot-economic protocol employing different triarylbismuth reagents. In literature, bis-aryl couplings with arylboronic acids were reported with good reactivity under different heating conditions for mono- and bis-arylations [29–30]. As mentioned before, our couplings employing triarylbismuths reacted on par with good reativity in addition to threefold coupling advantage with sub-stoichiometric loadings.…”

“…A trial reaction was performed with 2,3-dibromobenzofuran ( 1.1, 3.3 equiv) and tri( p -anisyl)bismuth (1 equiv) with Pd(OAc) 2 /PPh 3 , Cs 2 CO 3 (3 equiv) in N -methyl-2-pyrrolidone (NMP) at 90 °C for 1 h as protocol conditions [35]. This protocol furnished the preferential cross-coupling at the more electrophilic 2-Br position of 2,3-dibromobenzofuran ( 1.1 ) [29]. This reaction delivered 2-aryl-3-bromobenzofuran 2.1 in 46% yield (Table 1, entry 1) and the corresponding bis-arylation product involoving both 2- and 3-Br positions was not formed.…”

“…The corresponding coupling products 2.22 – 2.27 were obtained in high yields (Table 2, entries 22–27). It is to be mentioned at this stage that in comparison to similar cross-couplings carried out with aryl boronic acids [29], the present method with triarylbismuth reagents showed appreciable reactivity with threefold coupling advantage and extended substrate scope. The overall resulted regio- and chemo-selective couplings encouraged us to investigate further arylation studies with triarylbismuth reagents.…”

“…To note, synthetic functionalization under transition-metal-catalyzed conditions allows the preparation of multi-substituted benzofurans in a facile manner [23–28]. Langer et al reported the site-selective Suzuki–Miyaura reaction of 2,3-dibromobenzofuran with arylboronic acids under palladium catalyzed conditions [29–30]. Bach et al reported site-selective studies involving the Sonogashira, Negishi, Kumada cross-couplings employing 2,3-dibromobenzofuran and 2,3,5-tribromobenzofuran substrates [31–33].…”

ChemInform Abstract: Synthesis of Arylated Benzofurans by Regioselective Suzuki—Miyaura Cross‐Coupling Reactions of 2,3‐Dibromobenzofurans‐ and 2,3,5‐Tribromobenzofurans.

“…Site-selective Negishi and Kumada crosscoupling reactions of 2,3,5-tribromobenzofuran have also been reported [14]. Recently, we have reported site-selective Suzuki-Miyaura reactions of 2,3-dibromobenzofuran [17]. Multi-step syntheses of 3-substituted benzofurans in low overall yields have been reported [16].…”