One-pot synthesis of 2H-phenanthro[9,10-c]pyrazoles from isoflavones by two dehydration processes

Abstract

An environmentally friendly and efficient method was developed for one-pot synthesis of a series of 2H-phenanthro[9,10-c]pyrazoles in EtOH by two dehydration processes. Firstly, 3,4-diaryl-1H-pyrazoles were synthesized by the cyclocondensation of isoflavones and hydrazine hydrate in refluxing EtOH. Secondly, the final target products 2H-phenanthro[9,10-c]pyrazoles were given by photocyclization and dehydration of 3,4-diaryl-1H-pyrazoles in 1 : 1 (v/v) EtOH-H 2 O. The advantages of this method are catalyst-free, short synthetic routes, mild reaction conditions and easy work-up. In addition, the fluorescence properties of 2H-phenanthro[9,10-c]pyrazoles were determined. Scheme 1 The retrosynthetic analysis of 2H-phenanthro[9,10-c]pyrazoles. † Electronic supplementary information (ESI) available: 1 H NMR, 13 C NMR and HRMS spectra for all compounds.

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).…”

“…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.…”

Pot-economic synthesis of diarylpyrazoles and pyrimidines involving Pd-catalyzed cross-coupling of 3-trifloxychromone and triarylbismuth

“…26 In the second step, it was expected to undergo cyclocondensation with hydrazine involving nucleophilic attack of hydrazine (B), ring opening (C) followed by cyclocondensation to give 3,4-diarylpyrazole (D). 12 Whereas the formation of 4,5-diarylpyrimidines is expected to begin with the base-mediated ring opening of isoflavone 37,38 leading to F which undergoes condensation with guanidine to give 4,5-diarylpyrimidine (G).…”

“…10,11 Phenol-substituted pyrazoles can easily be converted to phenanthropyrazoles. 12 Apart from that, pyrazole derivatives are also known to serve as insecticides, 13 fungicides 14 and as versatile ligands. 15,16 There have been a few synthetic methods for the preparation of aryl substituted pyrazoles [17][18][19][20][21][22][23] and pyrimidines.…”