Abstract
4-Heteroarylidene-2-phenyl-1,3-oxazol-5(4H)-ones were prepared by reactions of hippuric acid with substituted furan-2-carboxaldehydes or furo[b]pyrrole type aldehydes. The reactivity of various furan-2-carboxaldehyde derivatives in this reaction is discussed. The effect of microwave irradiation on some condensation reactions was compared with "classical" conditions. The results show that microwave irradiation shortens the reaction times while affording comparable yields. Elementary analysis, UV, IR and 1D NMR proved the structure of new synthesised compounds. 2D NMR spectroscopic measurements confirmed that the configuration at the carbon-carbon double bond corresponds to the pure E isomers of the products.
Highlights
During the past few decades many results have been published in the area of the synthesis and the study of physical and chemical properties of heterocyclic compounds containing a furan ring connected to or fused with a benzene ring or with different heterocyclic systems
Substituted furan-2-carboxaldehydes 1a-e and furo[b]pyrrole type aldehydes 2a-e, 3a,b are heteroaromatic compounds which posses a C2 carbonyl group that may act as a reactive centre for various condensation reactions
We present the synthesis of 5-(2-bromophenyl)furan-2-carboxaldehyde (1a) by Meerweins method (Scheme 1)
Summary
During the past few decades many results have been published in the area of the synthesis and the study of physical and chemical properties of heterocyclic compounds containing a furan ring connected to or fused with a benzene ring or with different heterocyclic systems. The use of 1,3-oxazol-5(4H)-ones as starting materials for synthesis is well known They are used as convenient reagents for the synthesis of α,β unsaturated α-amino acids [8], cyclic analogues of natural amino acids [9] or as intermediates for the synthesis of new heterocyclic compounds [10]. The aim of this study was to synthesise some new condensation products of 1a-e, 2a-e and 3a,b by their reactions with hippuric acid (Schemes 2-4). The condensation products of aldehydes 1a-3b with hippuric acid catalysed by potassium acetate [18] were prepared in dry acetic anhydride as shown in Schemes 2-4. 5-Arylfuran-2-carboxaldehydes 1a-c reacted with hippuric acid giving (4E)-2-phenyl-4-{[5-(Rphenyl)-2-furyl]methylene}-1,3-oxazol-5(4H)-ones (3a-c) (Scheme 2) in high yields (70-83%) after short reaction times
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