Abstract
This review presents a survey of the condensations of 3-formylchromone with various active methylene and methyl compounds, e.g. malonic or barbituric acid derivatives, five-membered heterocycles, etc. The utilisation of the condensation products for the synthesis of different heterocyclic systems, which is based on the ability of the γ-pyrone ring to be opened by the nucleophilic attack is also reviewed. Finally, the applications of microwave irradiation as an unconventional method of reaction activation in the synthesis of condensation products is described and the biological activity of some chromone derivatives is noted.
Highlights
Introduction3-formylchromone (1, Figure 1) occupies an important position in the synthesis of various heterocyclic systems
From a synthetic viewpoint, 3-formylchromone (1, Figure 1) occupies an important position in the synthesis of various heterocyclic systems
This review presents the synthetic capability and the exploitation of the abovementioned types of condensation, achieved using the microwave irradiation method of synthesis as a new and very convenient rate enhancing method [4 -7]
Summary
3-formylchromone (1, Figure 1) occupies an important position in the synthesis of various heterocyclic systems. Several types of subsequent reactions of the condensation products illustrate the ability of chromone derivatives to serve as excellent precursors for the synthesis of a wide variety of heterocyclic systems. Condensation of 1 with an excess amount of 2,4-pentanedione (Scheme 2, path a) in boiling ethanol catalysed by ammonium acetate furnished 3-acetyl-5-(5-R-2-hydroxybenzoyl)-2-methylpyridines 9 in 20–29% yields [15]. The mechanism of this reaction involves the initial base-catalysed condensation of 1 with 2,4-pentanedione to obtain 3-[(4-oxo-4H-1-benzopyran-3-yl)methylene]pentanediones 7, followed by the cleavage of the pyrone ring at C-2 by ammonia and cyclisation of 7 to afford 9 via non-isolable intermediate 8. Benzophenone 14 is obtained by cyclisation of 12 to 13 and subsequent dehydration and tautomerisation
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