Abstract
An environmentally benign green protocol for the synthesis of 5-unsubstituted 3,4-dihydropyrimidin-2(1H)-ones using Amberlyst 15 DRY as a recyclable catalyst has been developed. The use of resinous, nontoxic, thermally stable, and inexpensive Amberlyst 15 DRY, as a recyclable heterogeneous catalyst, makes the process simple with negligible chemical waste. Among the various solid acid catalysts Amberlyst 15 DRY was found to be the most efficient catalyst with regard to reaction time, yield, and ease of work-up procedure.
Highlights
Replacement of conventional, toxic, and polluting Bronsted and Lewis acid catalysts with ecofriendly reusable solid acid heterogeneous catalysts like acidic zeolites, clays, sulfated zirconia, and ion exchange resins is an area of current interest [1, 2]
To evaluate the catalytic effect of various ion exchange resins we started with the model reaction of ethylacetoacetate (1.0 mmol) with benzaldehyde (1.0 mmol) and urea (1.2 mmol) in refluxing ethanol without and with use
It was found that 50 mg of Amberlyst 15 DRY is sufficient to carry out the Biginelli reaction successfully
Summary
Replacement of conventional, toxic, and polluting Bronsted and Lewis acid catalysts with ecofriendly reusable solid acid heterogeneous catalysts like acidic zeolites, clays, sulfated zirconia, and ion exchange resins is an area of current interest [1, 2]. Pyrimidinones or dihydropyrimidinones (DHPMs) are well known for their wide range of bioactivities Their applications in the field of drug research have stimulated the development of a wide range of synthetic methods for their preparation and chemical transformations. Out of the five major bases in nucleic acids three are pyrimidine derivatives which comprise of cytosine (1) which is found in DNA and RNA, uracil (2) in RNA and thymine, and (3) in DNA Because of their involvement as bases in DNA and RNA, they have become very important in the world of synthetic organic chemistry. Aryl-substituted 3,4-dihydropyrimidin2(1H)-one and their derivatives are an important class of substances in organic and medicinal chemistry (see Figure 1). In an attempt to prepare DHPMs, different types of acidic catalysts such as H2SO4 [12], BF3·EtOH/CuCl [13], LaCl3·7H2O with catalytic concentrated HCl [14], CeCl3·7H2O [15], InCl3 [16], heteropolyacids [17], BiCl3 [18], Cu(OTf)2 [19], TMSCl [20], LiClO4 [21], LiBr [22], ISRN Organic Chemistry
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