Abstract. The one-pot multicomponent synthesis of 3,4-dihydropyrimidinone derivatives using starch sulfuric acid as an environmentally friendly biopolymer-based solid acid catalyst from aldehydes, β-keto esters and urea/ thiourea without solvent is described. Compared with classical Biginelli reaction conditions, this new method has the advantage of minimizing the cost operational hazards and environmental pollution, good yields, shorter reaction times and simple work-up.Keywords: Biginelli reaction, dihydropyrimidinones, starch sulfuric acid, solvent-free, biodegradable catalyst.
IntroductionDihydropyrimidinones are attractive organic compounds which show important biological activities such as antiviral, antitumor, antibacterial and anti-infl ammatory actions [1][2][3]. The more convenient procedure for the preparation of dihydropyrimidinones fi rst reported by P. Biginelli in 1893, consists of the one-pot condensation of β-dicarbonyl compounds with aldehydes and urea or thiourea under strongly acidic conditions [4]. One major disadvantage of this method is the low yields especially in the case of aliphatic and some substituted aromatic aldehydes. To circumvent this problem, a variety of new catalysts has been introduced in the literature. In recent years, many protocols involving the use of Lewis and Bronsted acids such as graphite supported lanthanum chloride, [5] [32][33][34][35][36][37][38] are reported. However, at a practical level, these often require relatively harsh reaction conditions such as high reaction temperatures, expensive or highly acidic catalysts, and prolonged reaction times. In most of the cases stoichiometric amounts of catalyst are required in order to achieve good yields. In addition, most of the reactions require tedious work-up procedures and column purifi cation, which ultimately results in diminished yields. Therefore, in spite of a large number of methods reported for this transformation, there is still need to develop a more effi cient, simple, milder protocol using conservational catalyst.In recent years, the direction of science and technology has been shifting more towards eco-friendly, natural product resources and reusable catalysts. Thus, natural biopolymers are attractive candidates in the search for such solid support catalysts [39]. Starch as a one of the most common and easy to recover biopolymer become in the scope of many research [40, 41].We now report an effi cient catalyzed method for the synthesis of dihydropyrimidinones via the three-component reaction of β-dicarbonyl compounds with aldehydes and urea or thiourea under mild conditions (Scheme 1). To the best of our knowledge, the use of starch sulfuric acid (SSA) as a catalyst for the synthesis of dihydropyrimidinones previously has not been reported.
