The Domino Chromone Annulation and a Transient Halogenation-Mediated C–H Alkenylation toward 3-Vinyl Chromones

Abstract

Reported in this paper is a step economical method toward the general synthesis of 3-vinyl chromones via the reactions between readily available o-hydroxyphenyl enaminones and various alkenes. The domino C–H alkenylation and chromone annulation of the enaminones are involved, which enables the synthesis of 3-vinyl chromone products using both terminal and internal alkenes via a key process of transient C–H halogenation.

Recent advances in transition metal-free annulation toward heterocycle diversity based on the C–N bond cleavage of enaminone platform

“…In the past decade, a range of 3-hydrocarbon functionalized chromones, including 3-alkylated chromones, 22 3-fluoroalkylated chromones, 23 3-arylated chromones, 24 3-vinylated chromones, 25 3-alkynylated chromones 26 and 3-acylated chromones, 27 had been synthesized via carbon functionalization, subsequent chromone annulation and final deamination under different reaction conditions and these developments had been reviewed by Wan et al 1 b in 2019 and Yu et al 1 d in 2021, respectively. Accordingly, only updated works in the chromone synthesis via such cascade reactions are introduced in this review.…”

“…In the past decade, a range of 3-hydrocarbon functionalized chromones, including 3-alkylated chromones, 22 3-fluoroalkylated chromones, 23 3-arylated chromones, 24 3-vinylated chromones, 25 3-alkynylated chromones 26 and 3-acylated chromones, 27 In 2020, an array of 3-aryl chromones were prepared by Eosin Y-catalyzed reactions of diazonium salts and hydroxyarylenaminones via green LED irradiation in DMSO at room temperature (Scheme 8). 28a According to the results, broad ranges of both o-hydroxyarylenaminones and diazonium salts were investigated in this novel photo-Meerwein arylation successfully affording the corresponding 3-aryl chromones in good yields.…”

Diversity‐Oriented Synthesis of Flavones and Isoflavones via Palladium/Norbornene Cooperative Catalysis

“…A number of methods for the assembly of flavones and isoflavones have already been developed, which can be roughly divided into two categories. [ 5‐11 ] One is through Claisen condensation, [ 12 ] Baker‐Venkataraman reaction [ 13 ] or Vilsmeier‐Haack reaction [ 14 ] of aromatic compounds, but most of these transformations only construct C2 and C3 monosubstituted chromones. The other is direct derivatization of chromone skeletons.…”

Advances in the site-selective C-5, C-3 and C-2 functionalization of chromones via sp2 C–H activation

“…The selective functionalization at C-5, C-3 or C-2 positions of chromones by a direct functionalization method acts as a substitution for the classical cross-coupling reactions including Ullmann, Suzuki, Heck, Negishi, Goldberg, Buckwald-Hartwig, Sonogashira, Hiyama, Cadiot-Chodkiewicz, Stille and Kumada coupling, and the carbonylation coupling, which includes pre-functionalization or generation of halogen wastes. [57][58][59][60][61] The coupling reaction without prefunctionalization catalyzed by a transition metal or other metal-free methodologies with a directing group containing a substrate are more efficient and atom-economic pathways. 62,63 Dahye et al earlier in 2018 discussed the siteselective C-H functionalization of chromones and coumarins.…”