Regioselective Synthesis of Methyl 2,3-Dihydro-2-aryl Benzofuran-3-Carboxylates Using Thallium(III) Nitrate
作者:Mahavir S. Khanna、Om V. Singh、Chandra P. Garg、Ram. P. Kapoor
DOI:10.1080/00397919308009816
日期:1993.3.1
Abstract Flavanones (1a–d) undergo smooth ring contraction with thallium(III) nitrate in presence of perchloric acid and trimethyl orthoformate resulting in the formation of methyl 2,3-dihydro-2-arylbenzofuran-3-carboxylates (2a–d) in good yields. The mechanism of this oxidation has also been discussed.
Hypervalent Iodine Oxidation of Flavanones: A New Synthesis of Methyl 2-Aryl-2,3-dihydrobenzofuran-3-carboxylates by 1,2-Aryl Shift
作者:Om Prakash、Madan P. Tanwar
DOI:10.1246/bcsj.68.1168
日期:1995.4
Flavanones (1), on oxidation with (diacetoxyiodo)benzene-sulfuric acid (DIB–H2SO4) or (hydroxy)tosyloxy)iodo)benzene (HTIB) in trimethyl orthoformate, undergo facile ring contraction by 1,2-aryl shift, thereby yielding methyl 2-aryl-2,3-dihydrobenzofuran-3-carboxylates (4) as major products (40—80%). cis-3-Methoxyflavanones (5) and flavones (3) are the minor products formed in variable ratios.
Cyclization of a variety of chalcones to flavanones catalyzed by 1 mol% phosphomolybdic acid (PMA) supported on silica as a mild, efficient, and reusable catalyst was carried out in high yields. PMA-SiO2 is an efficient, inexpensive, and green catalyst which gave high conversion yields and could be recycled up to three times without significant loss in activity.
New synthesis of flavanones catalyzed by l-proline
L-Proline is utilized as an efficient organocatalyst for the synthesis of substituted flavanones and chalcones in good yields. The efficiency of the catalyst was proved with a variety of substrates ranging from electron-deficient to electron-rich aryl aldehydes and 2-hydroxyacetophenones. (c) 2005 Elsevier Ltd. All rights reserved.