Synthesis of heterocyclic-fused benzofurans via C–H functionalization of flavones and coumarins

Abstract

An efficient method to effect C-O cyclization was developed via the C-H functionalization of chromones and coumarins, affording heterocyclic-fused benzofurans.

Synthesis of heterocyclic-fused benzopyrans via the Pd(ii)-catalyzed C–H alkenylation/C–O cyclization of flavones and coumarins

“…Furthermore, the enhanced activity observed with Al 2 O 3 might be attributed to a pathway where Al 2 O 3 competes with Pd/Cu in chelating the chromone substrate. 8 The utility of the present reaction was broadened by conducting a series of experiments designed to explore the potential applicability of the methodology to the coumarin scaffold 4 (Table 3). Based on the proposed mechanism, we envisaged that the selective C-H functionalization/C-O cyclization reac- tions of the 4-arylcoumarins would be possible because electrophilic palladation of the coumarins at the C3 position was favorable due to the nucleophilic 3-position.…”

Transition Metal Mediated C–H Activation of 2‐Pyrones, 2‐Pyridones, 2‐Coumarins and 2‐Quinolones

“…The C–O cyclisation via C–H functionalisation of 2‐coumarins was reported by Hong (Scheme ) . The C–O cyclisation of 4‐arylcoumarins was ultimately possible due to the favourable metalation of the nucleophilic C‐3 position.…”

Coumarin heterocyclic derivatives: chemical synthesis and biological activity

“…58 The Hong group developed a C-H bond functionalization, with an intramolecular C-O cyclization of 4-(2 0 -hydroxyphenyl)-coumarins 57, in the presence of 1-2 equivalents of Cu(OAc) 2 and a catalytic amount of Zn(OTf) 2 , which afforded the corresponding 6H-benzofuro[2,3-c]coumarins 58 (Scheme 19). 59 The formation of these products can be explained by the coordination of a Cu(II) species with the phenolic hydroxyl group. Once a complex is generated, the electrophilic metalation at the C3-position of the chromone on Cu(II) may proceed.…”

“…196 In this context, some recent examples concerning the C-H functionalization at the C3 position of chromones and coumarins have been reported by the Hong group. 59,197 With these elements, Hong and co-workers carried out a practical approach for effecting tandem C-H alkenylation/C-O cyclization via the C-H functionalization of coumarin derivatives 57 to provide convenient access to coumarin-annelated benzopyrans 272 (Scheme 84). 198 …”