Ionic liquid promoted efficient synthesis of 3,4-dihydropyrimidin-2-(1 H )-ones
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Catalysis Letters Vol. 100, Nos. 3–4, April 2005 ( 2005) DOI: 10.1007/s10562-004-3451-8
Ionic liquid promoted efficient synthesis of 3,4-dihydropyrimidin2-(1H)-ones Ahmad Shaabani*, and Abbas Rahmati Department of Chemistry, Shahid Beheshti University, P.O. Box 19396-4716 Tehra, Iran
Received 16 November 2004; accepted 24 November 2004
R2 O
X
O
R2
R1=Alkyl or Aryl
R3
H2N
NH2
NH
O
TMGT R1CHO
R1
100 0C 5-50 min
X= O, S
R3
N H
X
(1-25)
R2=Alkyl-O or Alkyl
80-95%
R3=Methyl 3,4-Dihydropyrimidin-2-(1H)-ones have been synthesized in very short time with excellent yields in the presence of 1,1,3,3tetramethylguanidinium trifluoroacetate as a room temperature ionic liquid under solvent free conditions at 100 C. KEY WORDS: 1,1,3,3-tetrametylguanidinium trifluoroacetate; Biginelli reaction; dihydropyrimidinones; ionic liquid; one-pot condensation reaction.
1. Introduction Ionic liquids (ILs) are emerging as effective promoters and solvents for green chemical reaction. Over the past few years, a variety of catalytic reactions have been successfully conducted using ILs as solvents. Many interesting results have been obtained which demonstrate advantages of using ILs are alternative for organic solvents. Especially, one of the most important advantages of ILs is the behavior of solvophobic interactions that generate an internal pressure which promote the association of the reagents in a solvent cavity during the activation process and showed an acceleration of the multi-component reactions (MCRs) in comparison to conventional solvents [1–4]. Dihydropyrimidinones (DHPMs) and their derivatives are an important class of compounds in the field of pharmaceuticals and exhibit a wide spectrum of biological activities [4–6]. Owing to the versatile biological activity of these compounds introduction of an alternative synthetic methodology is of prime importance. Very recently, we reported NH4Cl as a catalyst for this transformation under solvent free conditions [7]. Despite NH4Cl is very cheap reagent and product yields * To whom correspondence should be addressed. E-mail: [email protected]
were relatively good, but the reaction times necessary for these yields were relatively long (3 h). Recently guanidine-based ILs was synthesized [8]. Herein, we wish to report the utilization of 1,1,3,3-tetrmethylguanidinium trifluoroacetate (TMGT), as a very efficient promoter for the multi-component Biginelli’s reaction. TMGT not only preserved the simplicity of Biginelli’s reaction, but also remarkably by improved the yields of products of dihydropyrimidinones (>80%) in shorter reaction times (5–50 min) in comparison of NH4Cl (Scheme 1).
2. Experimental Melting points were measured on an Electrothermal 9100 apparatus and are uncorrected. Mass spectra were recorded on a Finnigan-Mat 8430 mass spectrometer operating at an ionization potential of 70 eV. IR spectra were recorded on a Shimadzu IR-470 spectrometer. 1H and 13C NMR spectra were recorded on a Bruker DRX300 Avance spectrometer at 300.13 and 75.47 MHz, respectively. N
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