Photo-induced tandem cyclization of 3-iodoflavones with electron rich five-membered heteroarenes

Abstract

Vinyl radicals were generated from 3-iodoflavones under a mercury lamp and tandem cyclization reactions occurred with five-membered heteroarenes entailing two consecutive C-C bond formations to synthesize benzo[e]chromeno[2,3-g]indol-13(1H)-one derivatives. The tandem cyclization reactions worked in acetonitrile without any additives such as transition metals, ligands and oxidants, giving rise to a broad variety of novel polycyclic xanthone frameworks in good yield under mild and environmentally friendly reaction conditions.

α‐Substituted Chalcones: A Key Review

“…Later, a similar cyclization was published by Yang et al. (2017) [194] who reacted α‐Br‐chalcone with pyrroles in dry acetonitrile using irradiation with a high‐pressure mercury lamp (500 W) at ambient temperature (reaction 4, Figure 49); no transition metals were used in this method. In another article, Paria and coworkers [195] revealed a photoredox iridium complex catalyzed intermolecular couplings of α‐bromochalcones to olefins affording 3,4‐dihydronaphthalenes (reaction 5, Figure 49) that can be easily transformed to the corresponding naphthalenes and further cyclized to 5 H ‐benzo[c]fluorenes.…”

Recent advances in the synthesis of xanthones and azaxanthones

“…An excellent example that provides rapid access to polycyclic xanthones without the requirement of any transition-metal-catalyst and/or oxidant additives is a tandem cyclization via the coupling of 3-iodoflavones 154 with five-membered heteroarenes. 185 This procedure allowed the preparation of a broad variety of novel polycyclic xanthone frameworks with excellent regioselectivity in good yields under mild and environmentally friendly reaction conditions. Mechanistic studies unveiled that the reaction proceeds via two consecutive C-C bond formations after irradiation of the substrate and N-methylpyrrole in CH 3 CN using a high-pressure mercury lamp (500 W) at room temperature for 7 h (Scheme 20A).…”

“…The substrate scope was also extended to other five-membered heteroarenes, with the desired xanthone derivatives 155 being obtained in lower yields. 185 5.3.2 Via intramolecular [4 + 2] cyclization. Another procedure that allows the preparation of xanthone derivatives without the need for a transition metal catalyst consists of a phase transfer reagent promoted tandem ring-opening and ring-closing reaction of 3-(hepta-1,6-diyn-1-yl)chromone derivatives 156 followed by a intramolecular [4 + 2] cyclization.…”

“…An intramolecular Diels-Alder reaction where both of the pyrone and the second aromatic rings are forged in a single step was reported for the synthesis of xanthones. 192 The scope of the route to several substituted xanthones was tested by using different 2′-hydroxyacetophenones (185) to prepare the corresponding 1,2-dichlorovinyloxy acetophenones (186 and 188) that react in situ with cinnamaldehyde (Scheme 24C). Similarly, the scope of the reaction was also 193 The scope and limitation of this reaction were studied and it was found that in addition to a 2-bromo substituted substrate, 2-fluoro or 2-chloro derivatives could also be obtained.…”

Synthesis of (2-Aminophenyl)(naphthalen-2-yl)methanones via Intramolecular Rearrangement of (E)-3-Styrylquinolin-4(1H)-ones under Irradiation with 365 nm UV Light

“…dehydrogenation/dehydration for the synthesis of polyheterocyclic componds, [20][21][22][23][24][25][26] we would like to follow our interest and demonstrate the intramolecular rearrangement of (E)-3-arylvinyl-4H-chromen-4-ones under UV light (365 nm/Ar) at room temperature for the synthesis of (2-aminophenyl)(naphthalen-2-yl)methanones analogues (Scheme 2), which avoids a) high temperature, b) usage of transition metals and c) directly constructed the naphthalene ring during rearrangement rather than inherited from substrates.…”