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Title: Facile synthesis of new substituted aryl and heteroarylflavones by thermal and microwave assisted Suzuki-Miyaura coupling reaction
Authors: Joshi, Vidya
Hatim, Jaywant Govind
Keywords: Suzuki-Miyaura coupling;Flavones;Biphenyl derivatives;Boronic acids;4′-bromoflavone;Microwave heating
Issue Date: Jul-2012
Publisher: NISCAIR-CSIR, India
Abstract: Microwave assisted Suzuki-Miyaura coupling of 4'-bromoflavone 5 with substituted aryl and heteroarylboronic acids 6a-m gives high yields of aryl and heteroarylflavones 7a-m. Couplings have been carried out by three methods i) conventional heating with Pd(OCOCH3)2 catalyst, in solvent DMF(N,N-dimethylformamide) and base, aqueous Na2CO3 (2N) for 6-12 hr, at 110°C, yield 30-70%, ii) conventional heating with Pd[(C6H5)3P]4 catalyst, in DMF and base, aq. Na2CO3 (2N) for 6-12 hr, at 110°C, yield 40-72% and iii) Microwave heating with Pd[(C6H5)3P]4 catalyst, in solvent (DMF+H2O, 5:2) and base, aq. Na2CO3 (2N) for 2-9 min, yield 50-87%. The substrate 4′-bromoflavone 5 has been synthesized from o-hydroxyacetophenone 1 in 3 steps. Esterification of 1 with 4-bromobenzoyl chloride 2 with montmorillonite-KSF catalyst, DCE (1,2-dichloroethane) and Et3N (triethylamine) which gives 2-(4-bromobenzoyloxy)acetophenone 3. Baker-Venkataraman rearrangement of 3 with pyridine and KOH further gives 1-(4-bromophenyl)-3-(2-hydroxyphenyl)propane-1,3-dione 4, followed by cyclization of 4 with methanolic sulfuric acid (2.5%) which yields 4'-bromoflavone 5, yield 82%.
Page(s): 1002-1010
ISSN: 0975-0983(Online); 0376-4699(Print)
Appears in Collections:IJC-B Vol.51B(07) [July 2012]

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