Synthesis of 3-heteroarylchromones via a photochemical reaction

Abstract

The direct coupling of 3-iodochromen-4-ones with heteroaromatics has been achieved via a photochemical reaction. A variety of 3-heteroarylchromones was obtained in moderate to good yields from the corresponding 3-iodochromen-4-ones and heteroaromatics, such as pyrrole, furan, thiophene, and benzofuran. The reaction worked smoothly in acetonitrile under a mercury lamp without any additives, providing a catalyst- and base-free approach for the synthesis of 3-heteroarylchromones.

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

“…Due to the ring closure for the formation of an aromatic system (vide infra), the stability issue 22 was not observed with the current protocol. The cyclization of 3-iodoavone 1a also proceeded smoothly with furan 2c and thiophene 2d to give the corresponding products in fair yields (entries [18][19]. It is noteworthy that no cyclization products were observed for benzene or other six-membered aromatics under the optimal conditions.…”

“…Various p-excessive ve-membered heteroarenes 2 were also explored to examine their compatibility and reactivity (entries [17][18][19]. Thus, irradiation of 1i with pyrrole 2b in MeCN at room temperature for 10 h gave the cyclization product 3q (entry 17).…”

“…On the basis of the experimental results and literature, 19,20,24,25 a two-step mechanism for the cyclization of 3-iodoavones 1 with p-excessive ve-membered heteroarenes 2 has been proposed. Initially, the photo-induced hemolytic cleavage of the C-I bond of 1 under UV light irradiation gave the radical intermediate A.…”

“…Following our interest in the photo-reactions of chromone analogues [18][19][20][21] as well as nucleoside substrates, 22 we herein report a new photo-induced tandem cyclization of 3-iodoavones with p-excessive ve-membered heteroaromatics at ambient temperature without the requirement of any transition-metal-catalyst and/or oxidant additives.…”

Stille coupling for the synthesis of isoflavones by a reusable palladium catalyst in water

“…Conventional synthetic methods for the preparation of isoflavones include deoxybenzoin cyclization of 2-hydroxyphenylbenzylketones, [7][8][9][10][11][12][13][14][15][16] oxidative rearrange ment, [17][18][19][20][21][22] or epoxidation [23] of a chalcone to form isoflavones, N-heterocyclic carbene-catalyzed reactions, [24,25] intramolecular [2+2] ketene cycloadditions, [26] reduction and cyclization of isoxazole derivatives, [27] and oxidation of flavanones. [20,[28][29][30][31] Recently, coupling of 3-iodochromones with heteroaromatics by a photochemical process, [32] and K10 montmorillonite-catalyzed one-pot reactions of 1-(2-hydroxyphenyl)butane-1,3-diones and 2,5-dimethoxy-2,5-dihydrofuran [33] to produce 3-heteroarylchromones were also reported.…”