H Functionalized Ionic Liquid Based on DABCO: New and Efficient

Hindawi Publishing CorporationJournal of ChemistryVolume 2013 Article ID 235818 5 pageshttpdxdoiorg1011552013235818

Research ArticleBi-SO3H Functionalized Ionic LiquidBased on DABCO New and Efficient Catalyst forFacile Synthesis of Dihydropyrimidinones

Firouzeh Nemati and Sara G Alizadeh

Department of Chemistry Semnan University Semnan 35131-19111 Iran

Correspondence should be addressed to Firouzeh Nemati fnemati 1350yahoocom

Received 25 May 2013 Revised 11 July 2013 Accepted 13 July 2013

Academic Editor Angelo de Fatima

Copyright copy 2013 F Nemati and S G AlizadehThis is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in anymedium provided the originalwork is properly cited

A simple and efficient method for the one-pot Biginelli condensation reaction of aldehydes 120573-dicarbonyl compounds and urea orthiourea employing [DABCO](SO

3H)2Cl2as a novel ionic liquid catalyst is described

1 Introduction

Over the past decade ionic liquids have attracted extensiveinterest in organic synthesis which has been recognized bya number of articles covering various aspects of ionic liquidsas the catalyst or as dual catalyst-solvent in synthetic organicchemistry [1 2] With increasing environmental concernsthe design of simple easily separable nontoxic and low-cost acidic ionic liquids has become an important researchfield [3ndash5] In this context ionic liquids as homogenousacid catalyst have attracted a great deal of attention dueto their outstanding properties such as simple preparationundetectable vapor pressure nonflammability and high ther-mal stability Introduction of functional groups especiallythe SO

3H-functional group obviously enhanced their acidity

andwater solubilityThese functionalized ILs are designed fora special use and are referred to as ldquotask-specific ILsrdquo

Multicomponent reactions (MCRs) defined as one-potreactions in which at least three different substrates jointhrough covalent bonds have steadily gained importancein synthetic organic chemistry MCRs allow the creation ofseveral bonds in a single operation and offer remarkableadvantages like simple procedure high bond forming effi-ciency time and energy saving extraction and purificationprocesses and hence minimize waste generation [6ndash10]MCRs are useful for the expedient creation of chemical

libraries of drug-like compounds with high levels of molec-ular complexity and diversity thereby facilitating identifi-cationoptimization in drug discovery programmes [11ndash16]Therefore researchers havemade great efforts to develop newMCRs with green procedure especially in the areas of drugdiscovery organic synthesis and material science [17 18]

In this paper a novel bi-SO3H functionalized ionic liquid

based onDABCOwas designed as a simple and powerful acidcatalyst and applied for synthesis of dihydropyrimidinones inmild reaction condition

2 Materials and Methods

21 Procedure for the Preparation of Ionic Liquid A round-bottomed flask (100mL) was charged with a solution of14-diazabicyclo[222]octane DABCO (056 g 5mmol) indry CH

2Cl2(50mL) and then chlorosulfonic acid (121 g

104mmol) was added dropwise over a period of 10min atroom temperature After the addition was completed thereaction mixture was left for 1 hour In this period of timea white solid was produced Afterward the CH

2Cl2was

decanted The residue was triturated with dry diethyletherand dried under vacuum to give [DABCO](SO

3H)2Cl2as a

very viscous colorless oil at 98 yieldSpectral data of [DABCO](SO

3H)2Cl2 1HNMR

(300MHz DMSO-d6) 120575 (ppm) 35 (s 6H) 732 (s 1H)

2 Journal of Chemistry

N

N

N

N

+

+

+

2ClSO3HDry CH2Cl2

Clminus

Clminus

SO3H

HO3S

Scheme 1 Synthesis of brnsted acidic ionic liquid

13CNMR (75MHz DMSO-d6) 120575 (ppm) 432 MSmz = 346

(M+ + 1) 345 (M+) IR (KBr cmminus1) 120592max 3500-2800 (broad)1319 (N-SO

2) 1179 (N-SO

2) Calcd For C

6H14N2S2O6Cl2 C

2086 H 405 N 811 Found C 2063 H 431 N 789

22 General Procedure for the Synthesis of Dihydropyrim-idinones Derivatives Aldehydes (1mmol) ethyl acetoac-etate (1mmol) and urea or thiourea (15mmol) were dis-solved in 4mL of ethanol containing [DABCO](SO

3H)2Cl2

(007mmol 0024 g) The mixture was heated under refluxAfter completion of the reaction as monitored by TLC water(10mL) was added to the reaction mixtureThe solid productwas filtered dried and recrystallized from ETOH to give thepure product

3 Results and Discussion

In continuation with our interest in developing efficient andenvironmental benign synthetic methodologies [19ndash21] wehave prepared a new type of brnsted acidic ionic liquidcatalyst based on DABCO and found that it is highly activefor the synthesis of dihydropyrimidinones

To prepare the brnsted acidic ionic liquid [DABCO](SO3H)2Cl2 chlorosulfonic acid (2 equiv) was added drop-

wise to a solution ofDABCO (1 equiv) in dry CH2Cl2at room

temperature (Scheme 1)For identification of structure of ionic liquid we have

studied the 1H NMR spectra of [DABCO](SO3H)2Cl2 The

presence of sulfonate groups causes a significant downfieldshift of the hydrogens of ionic liquid (35120575) compared withDABCO (27120575) Acidic hydrogens of SO

3H groups were

observed in 732 ppm that confirmed the sulfur atoms inthe catalyst were connected to nitrogen atoms of DABCO[5] Furthermore according to the literature reports in thereaction of triethylamine 1-methyl imidazole or imidazolewith chlorosulfonic acid the nitrogen atoms of amines act asa nucleophile (not base) and attack the sulfur atomofClSO

3H

[22]Thermogravimetric analysis (TGA) was used to study the

thermal stability of the acid catalyst (Figure 1) The catalyst isstable up to 250∘C and it is safe to carry out the reaction at80ndash140∘C which is sufficient for organic reaction

To investigate the efficiency and applicability of the newcatalyst its role as brnsted acidic ionic liquid was evaluatedfor synthesis of dihydropyrimidinones (DHPMs) derivativesin EtOH under mild heating (Scheme 2)

For optimization of the reaction condition ethyl acetoac-etate (1mmol) benzaldehyde (1mmol) and urea (15mmol)

100

10

Wei

ght (

)

20 100 200 300 400 500Temperature (∘C)

00

minus095

Der

ivat

ive w

eigh

t (

)

Figure 1 The TGA curve of [DABCO](SO3H)2Cl2

were heated under refluxing EtOH in the presence of[DABCO](SO

3H)2Cl2

(007mmol) to afford ethyl-6-methyl-2-oxo-4-phenyl-1234-tetrahydropyrimidine-5-car-boxylate in 98 yield (Table 1 Entry 1) To check the realeffect of the catalyst the reaction was performed without[DABCO](SO

3H)2Cl2The yield of catalyst-free reaction was

lower than 12 Further we carried out the above reactionwith ClSO

3H as catalyst (014mmol 007 g) in the same

reaction condition it leads to several very close spots onTLC and the desired product could not be isolated

The promising results obtained with [DABCO](SO3H)2Cl2prompted us to further investigate the effect

of solvents on Biginelli reactions So the model reactionwas performed in various solvents such as EtOH MeOHacetonitrile THF and CH

2Cl2under reflux and it was

found that EtOH provided the best solvents because of yieldreaction rate cost and environmental acceptability Furtherexperments revealed the optimum amount of catalyst to be007mmol

Structural varieties of arylaldehydes have been success-fully utilized for this transformation and in most cases goodyields were obtained (Table 1)

The reaction in refluxing ethanol alone gave poor yieldsIt is also a well-established fact that brnsted ionic liquidsproducedH+ Based on these two facts a possiblemechanismis depicted in Scheme 3 [23]

Table 2 compares the efficiency of the present methodfor the synthesis of 34-dihydropyrimidine-2-(1H)-ones withother reported catalysts in the literature As can be seen[DABCO](SO

3H)2Cl2acts as a highly effective catalyst in

terms of time temperature and yield of the reaction

4 Conclusion

In summary a novel and highly efficient methodology forthe synthesis of DHPMs in the presence of catalytic amountsof novel ionic liquid [DABCO](SO

3H)2Cl2 under reflux

conditions is reported This protocol describes a nonmetalcatalyst safe and easy work-up procedure for the synthesis

Journal of Chemistry 3

OR

O O X

+ +

NH

NH

X

Ar

RO

O

EtOH reflux IL

X = O S

ArCHO

R = Et Me

H2N NH2

Scheme 2 Application of [DABCO](SO3H)2Cl2(IL) in the Biginelli reaction

O

HN

O

OH

OH

HO

O

NH

NHNH

O

O

EtO

EtO EtO

EtO

O OO

O

Ar

Ar

ArAr

Ar

C HOH

+

+

+

+ +

Cyclization

IL

+ IL H

IL H

H

H

HN

O

H

H2N

H2N

NH2NH2

NH2minusH2O

minusH2O

= [DABCO] (SO3H)2Cl2

Scheme 3 A plausible mechanism

Table 1 [DABCO](SO3H)2Cl2-catalyzed synthesis of dihydropyrimidinones derivatives in EtOH

Entry Ar X R Time (min) Yield ()a Mp (Lit)∘Cb

1 C6H5 O Et 35 98 203-204 (202ndash204) [24]2 4-FndashC6H4 O Et 70 87 181ndash183 (183ndash185) [25]3 4-MeOndashC6H4 O Et 70 90 206ndash208 (206ndash208) [24]4 3-MeOndashC6H4 O Et 80 88 207ndash209 (207-208) [26]5 2-ClndashC6H4 O Et 80 83 220ndash222 (222ndash224) [26]6 4-ClndashC6H4 O Et 50 85 211ndash216 (208ndash211) [27]7 4-MeC6H4 O Et 75 83 214ndash216 (215ndash217) [27]8 3-NO2ndashC6H4 O Et 55 91 228ndash232 (229ndash231) [27]9 4-NO2ndashC6H4 O Et 45 93 208ndash211 (208ndash210) [24]10 C6H5 S Et 55 89 206-207 (206-207) [27]11 4-NO2ndashC6H4 S Et 120 75 110ndash113 (109ndash111) [27]12 C6H5 O Me 40 93 209-210 (206ndash208) [27]13 4-MeOndashC6H4 O Me 75 82 190ndash192 (190ndash192) [27]14 4-NO2 C6H4 O Me 55 82 213ndash215 (214-215) [27]aIsolated yieldsbProducts were characterized by comparison of their spectroscopic data (1H NMR IR) and melting points with those reported in the literature

Table 2 Comparison of the results obtained for the synthesis of 34-dihydropyrimidine-2-(1H)-ones catalyzed by [DABCO](SO3H)2Cl2 withother recently reported catalysts

Catalyst Condition Time Yield () ReferencesSulfonated carbon Neat140∘C 15ndash30min 80ndash92 [26][Hmim]HSO4 Neat80∘C 25ndash50min 88ndash96 [28]Bioglycerol-based carbon catalyst Neat75ndash80∘C 4ndash45 h 80ndash91 [29]HClO4ndashSiO2 Neat100∘C 75ndash180min 83ndash91 [30]119901-sulfonic acid calixarenes EtOHreflux 6 h 56ndash92 [31]L-pyrrolidine-2-carboxylic acid-4-hydrogen sulfate supported on silica gel EtOHreflux 6 h 80ndash98 [32][DABCO](SO3H)2Cl2 EtOHreflux 35ndash120min 75ndash98 This work


of these products In addition simplicity and ease of prepa-ration of the catalyst are promising points for the presentedmethodology

Acknowledgments

The authors thank the Department of Chemistry and Officeof Gifted Student at Semnan University for their financialsupport

References

[1] A C Cole J L Jensen I Ntai et al ldquoNovel broslashnsted acidicionic liquids and their use as dual solvent-catalystsrdquo Journal ofthe American Chemical Society vol 124 no 21 pp 5962ndash59632002

[2] X Liu H Ma Y Wu et al ldquoEsterification of glycerol withacetic acid using double SO

3H-functionalized ionic liquids as

recoverable catalystsrdquo Green Chemistry vol 13 no 3 pp 697ndash701 2011

[3] R Kore T J Dhilip Kumar and R Srivastava ldquoHydration ofalkynes using Bronsted acidic ionic liquids in the absence ofNobel metal catalystH

2SO4rdquo Journal of Molecular Catalysis A

vol 360 pp 61ndash70 2012[4] B Garg and Y C Ling ldquoHighly efficient synthesis of

N-confused meso-tetraspirocyclohexyl calix[4]pyrrole usingBroslashnsted acidic ionic liquids as catalystsrdquo Tetrahedron Lettersvol 53 pp 5674ndash5677 2012

[5] M A Zolfigol A Khazaei A R Moosavi-Zare A Zare andV Khakyzadeh ldquoRapid synthesis of 1-amidoalkyl-2-naphtholsover sulfonic acid functionalized imidazolium saltsrdquo AppliedCatalysis A vol 400 no 1-2 pp 70ndash81 2011

[6] A Basso L Banfi R Riva and G Guanti ldquoA novel highlyselective chiral auxiliary for the asymmetric synthesis of L- andD-120572-amino acid derivatives via amulticomponent ugi reactionrdquoJournal of Organic Chemistry vol 70 no 2 pp 575ndash579 2005

[7] S T Staben and N Blaquiere ldquoFour-component synthesis offully substituted 124-triazolesrdquo Angewandte Chemie vol 49no 2 pp 325ndash328 2010

[8] T Yue M-X Wang D-X Wang G Masson and J Zhu ldquoCat-alytic asymmetric Passerini-type reaction Chiral aluminum-organophosphate-catalyzed enantioselective 120572-addition of iso-cyanides to aldehydesrdquo Journal of Organic Chemistry vol 74 no21 pp 8396ndash8399 2009

[9] B A Trofimov L V Andriyankova K V Belyaeva et al ldquoC2-functionalization of 1-substituted imidazoles with aldehydesand electron-deficient acetylenes a novel three-componentreactionrdquo European Journal of Organic Chemistry no 9 pp1772ndash1777 2010

[10] N Ma B Jiang G Zhang S-J Tu W Wever and GLi ldquoNew multicomponent domino reactions (MDRs) inwater highly chemo- regio- and stereoselective synthe-sis of spiro[13]dioxanopyridine-46-diones and pyrazolo[34-b]pyridinesrdquoGreen Chemistry vol 12 no 8 pp 1357ndash1361 2010

[11] J D Sunderhaus C Dockendorff and S F Martin ldquoApplica-tions of multicomponent reactions for the synthesis of diverseheterocyclic scaffoldsrdquo Organic Letters vol 9 no 21 pp 4223ndash4226 2007

[12] C Haurena E Le Gall S Sengmany T Martens and MTroupel ldquoA Straightforward three-component synthesis of 120572-amino esters containing a phenylalanine or a phenylglycine

scaffoldrdquo Journal of Organic Chemistry vol 75 no 8 pp 2645ndash2650 2010

[13] B Willy and T J J Muller ldquoRegioselective three-componentsynthesis of highly fluorescent 135-trisubstituted pyrazolesrdquoEuropean Journal of Organic Chemistry no 24 pp 4157ndash41682008

[14] M M Heravi B Baghernejad H A Oskooie and R Hek-matshoar ldquoA novel and facile synthesis of 2-(cyclohexylamino)-67-dihydro-3-aryl-1H-indole-4(5H)-ones via a one-pot multi-component reactionrdquo Tetrahedron Letters vol 49 no 42 pp6101ndash6103 2008

[15] M Adib E Sheikhi A Kavoosi and H R BijanzadehldquoSynthesis of 2-(alkylamino)-5-alkyl[(2-oxo-2H-chromen-3-yl)carbonyl]amino-34-furandicarboxylates using a multi-component reaction in waterrdquo Tetrahedron vol 66 no 47 pp9263ndash9269 2010

[16] W-B Chen Z-J Wu Q-L Pei L-F Cun X-M Zhangand W-C Yuan ldquoHighly enantioselective construction ofspiro[4H-pyran-331015840-oxindoles] through a domino knoeve-nagelMichaelcyclization sequence catalyzed by cupreinerdquoOrganic Letters vol 12 no 14 pp 3132ndash3135 2010

[17] S-L Wang F-Y Wu C Cheng et al ldquoMulticomponentsynthesis of poly-substituted benzo[a]pyrano-[2 3-c]phenazinederivatives under microwave heatingrdquo ACS Combinatorial Sci-ence vol 13 no 2 pp 135ndash139 2011

[18] S R Kolla and Y R Lee ldquoEfficient one-pot synthesis of120573-phosphono malonates and 2-amino-4H-chromen-4-ylphos-phonate derivatives by ethylenediamine diacetate-catalyzedthree-component reactionsrdquoTetrahedron vol 68 no 1 pp 226ndash237 2012

[19] F Nemati andA Beyzai ldquoA facile one-pot solvent-free synthesisof 1 2-dihydro-1 arylnaphtho[1 2-e][1 3]oxazine-3-ones cat-alyzed bywet cyanuric chloriderdquo Journal of Chemistry vol 2013Article ID 365281 4 pages 2013

[20] F Nemati and R Saeedirad ldquoNano-Fe3O4encapsulated-silica

particles bearing sulfonic acid groups as a magnetically separa-ble catalyst for green and efficient synthesis of functionalizedpyrimido[4 5-b]quinolines and indeno fused pyrido[2 3-d]pyrimidines in waterrdquo Chinese Chemical Letters vol 24 pp370ndash372 2013

[21] F Nemati and A Elhampour ldquoCellulose sulphuric acid asa biodegradable catalyst for conversion of aryl amines intoazides at room temperature under mild conditionsrdquo Journal ofChemical Society vol 124 no 4 pp 889ndash892 2012

[22] H R Shaterian and M Ranjbar ldquoAn environmental friendlyapproach for the synthesis of highly substituted imidazolesusing Broslashnsted acidic ionic liquid N-methyl-2-pyrrolidoniumhydrogen sulfate as reusable catalystrdquo Journal of MolecularLiquids vol 160 no 1 pp 40ndash49 2011

[23] R O M A De Souza E T Da Penha H M S Milagre et alldquoThe three-component biginelli reaction a combined experi-mental and theoretical mechanistic investigationrdquo Chemistryvol 15 no 38 pp 9799ndash9804 2009

[24] E H Hu D R Sidler and U-H Dolling ldquoUnprece-dented catalytic three component one-pot condensation reac-tion an efficient synthesis of 5-alkoxycarbonyl-4-aryl-34-dihydropyrimidin-2(H)-onesrdquo Journal of Organic Chemistryvol 63 no 10 pp 3454ndash3457 1998

[25] D Z Xu H Li and Y Wang ldquoHighly enantioselective Biginellireaction catalyzed by a simple chiral primary amine catalystasymmetric synthesis of dihydropyrimidinesrdquo Tetrahedron vol68 no 38 pp 7867ndash7872 2012


[26] M Moghaddasi A Davoodnia M M Heravi and N THoseini ldquoSulfonated carbon catalyzed Biginelli reaction forone-pot synthesis of 3 4-dihydropyrimidin-2(H)-ones andthionesrdquo Chinese Journal of Catalyst vol 33 pp 706ndash710 2012

[27] N-Y Fu Y-F Yuan Z Cao S-W Wang J-T Wang and CPeppe ldquoIndium(III) bromide-catalyzed preparation of dihy-dropyrimidinones improved protocol conditions for the Big-inelli reactionrdquoTetrahedron vol 58 no 24 pp 4801ndash4807 2002

[28] H Kefayati F Asghari and R Khanjanian ldquo1-Methylimid-azolium hydrogen sulfatechlorotrimethylsilane an effectivecatalytic system for the synthesis of 3 4-dihydropyrimidin-2(1H)-ones and hydroquinazoline-2 5-dionesrdquo Journal ofMolecular Liquids vol 172 pp 147ndash151 2012

[29] K Konkala N M Sabbavarapu R Katla et al ldquoRevisit to theBiginelli reaction a novel and recyclable bioglycerol-based sul-fonic acid functionalized carbon catalyst for one-pot synthesisof substituted 34-dihydropyrimidin-2-(1H)-onesrdquo TetrahedronLetters vol 53 no 15 pp 1968ndash1973 2012

[30] S R Narahari B R Reguri O Gudaparthi and K MukkantildquoSynthesis of dihydropyrimidinones via Biginelli multi-com-ponent reactionrdquo Tetrahedron Letters vol 53 no 13 pp 1543ndash1545 2012

[31] D L Da Silva S A Fernandes A A Sabino and A Fatimaldquop-Sulfonic acid calixarenes as efficient and reusable organocat-alysts for the synthesis of 34-dihydropyrimidin-2(1H)-ones-thionesrdquo Tetrahedron Letters vol 52 no 48 pp 6328ndash63302011

[32] A Ghorbani-Choghamarani and P Zamani ldquoThree com-ponent reactions an efficient and green synthesis of 3 4-dihydropyrimidin-2-(1H)-ones and thiones using silica gel-supported L-pyrrolidine-2-carboxylic acid-4-hydrogen sulfaterdquo2013

Impact Factor 173028 Days Fast Track Peer ReviewAll Subject Areas of ScienceSubmit at httpwwwtswjcom

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawi Publishing Corporation httpwwwhindawicom Volume 2013

The Scientific World Journal


N

N

N

N

+

+

+

2ClSO3HDry CH2Cl2

Clminus

Clminus

SO3H

HO3S

Scheme 1 Synthesis of brnsted acidic ionic liquid

13CNMR (75MHz DMSO-d6) 120575 (ppm) 432 MSmz = 346

(M+ + 1) 345 (M+) IR (KBr cmminus1) 120592max 3500-2800 (broad)1319 (N-SO

2) 1179 (N-SO

2) Calcd For C

6H14N2S2O6Cl2 C

2086 H 405 N 811 Found C 2063 H 431 N 789

22 General Procedure for the Synthesis of Dihydropyrim-idinones Derivatives Aldehydes (1mmol) ethyl acetoac-etate (1mmol) and urea or thiourea (15mmol) were dis-solved in 4mL of ethanol containing [DABCO](SO

3H)2Cl2

(007mmol 0024 g) The mixture was heated under refluxAfter completion of the reaction as monitored by TLC water(10mL) was added to the reaction mixtureThe solid productwas filtered dried and recrystallized from ETOH to give thepure product

3 Results and Discussion

In continuation with our interest in developing efficient andenvironmental benign synthetic methodologies [19ndash21] wehave prepared a new type of brnsted acidic ionic liquidcatalyst based on DABCO and found that it is highly activefor the synthesis of dihydropyrimidinones

To prepare the brnsted acidic ionic liquid [DABCO](SO3H)2Cl2 chlorosulfonic acid (2 equiv) was added drop-

wise to a solution ofDABCO (1 equiv) in dry CH2Cl2at room

temperature (Scheme 1)For identification of structure of ionic liquid we have

studied the 1H NMR spectra of [DABCO](SO3H)2Cl2 The

presence of sulfonate groups causes a significant downfieldshift of the hydrogens of ionic liquid (35120575) compared withDABCO (27120575) Acidic hydrogens of SO

3H groups were

observed in 732 ppm that confirmed the sulfur atoms inthe catalyst were connected to nitrogen atoms of DABCO[5] Furthermore according to the literature reports in thereaction of triethylamine 1-methyl imidazole or imidazolewith chlorosulfonic acid the nitrogen atoms of amines act asa nucleophile (not base) and attack the sulfur atomofClSO

3H

[22]Thermogravimetric analysis (TGA) was used to study the

thermal stability of the acid catalyst (Figure 1) The catalyst isstable up to 250∘C and it is safe to carry out the reaction at80ndash140∘C which is sufficient for organic reaction

To investigate the efficiency and applicability of the newcatalyst its role as brnsted acidic ionic liquid was evaluatedfor synthesis of dihydropyrimidinones (DHPMs) derivativesin EtOH under mild heating (Scheme 2)

For optimization of the reaction condition ethyl acetoac-etate (1mmol) benzaldehyde (1mmol) and urea (15mmol)

100

10

Wei

ght (

)

20 100 200 300 400 500Temperature (∘C)

00

minus095

Der

ivat

ive w

eigh

t (

)

Figure 1 The TGA curve of [DABCO](SO3H)2Cl2

were heated under refluxing EtOH in the presence of[DABCO](SO

3H)2Cl2

(007mmol) to afford ethyl-6-methyl-2-oxo-4-phenyl-1234-tetrahydropyrimidine-5-car-boxylate in 98 yield (Table 1 Entry 1) To check the realeffect of the catalyst the reaction was performed without[DABCO](SO

3H)2Cl2The yield of catalyst-free reaction was

lower than 12 Further we carried out the above reactionwith ClSO

3H as catalyst (014mmol 007 g) in the same

reaction condition it leads to several very close spots onTLC and the desired product could not be isolated

The promising results obtained with [DABCO](SO3H)2Cl2prompted us to further investigate the effect

of solvents on Biginelli reactions So the model reactionwas performed in various solvents such as EtOH MeOHacetonitrile THF and CH

2Cl2under reflux and it was

found that EtOH provided the best solvents because of yieldreaction rate cost and environmental acceptability Furtherexperments revealed the optimum amount of catalyst to be007mmol

Structural varieties of arylaldehydes have been success-fully utilized for this transformation and in most cases goodyields were obtained (Table 1)

The reaction in refluxing ethanol alone gave poor yieldsIt is also a well-established fact that brnsted ionic liquidsproducedH+ Based on these two facts a possiblemechanismis depicted in Scheme 3 [23]

Table 2 compares the efficiency of the present methodfor the synthesis of 34-dihydropyrimidine-2-(1H)-ones withother reported catalysts in the literature As can be seen[DABCO](SO

3H)2Cl2acts as a highly effective catalyst in

terms of time temperature and yield of the reaction

4 Conclusion

In summary a novel and highly efficient methodology forthe synthesis of DHPMs in the presence of catalytic amountsof novel ionic liquid [DABCO](SO

3H)2Cl2 under reflux

conditions is reported This protocol describes a nonmetalcatalyst safe and easy work-up procedure for the synthesis


OR

O O X

+ +

NH

NH

X

Ar

RO

O

EtOH reflux IL

X = O S

ArCHO

R = Et Me

H2N NH2


O

HN

O

OH

OH

HO

O

NH

NHNH

O

O

EtO

EtO EtO

EtO

O OO

O

Ar

Ar

ArAr

Ar

C HOH

+

+

+

+ +

Cyclization

IL

+ IL H

IL H

H

H

HN

O

H

H2N

H2N

NH2NH2

NH2minusH2O

minusH2O










Acknowledgments


References












































OR

O O X

+ +

NH

NH

X

Ar

RO

O

EtOH reflux IL

X = O S

ArCHO

R = Et Me

H2N NH2


O

HN

O

OH

OH

HO

O

NH

NHNH

O

O

EtO

EtO EtO

EtO

O OO

O

Ar

Ar

ArAr

Ar

C HOH

+

+

+

+ +

Cyclization

IL

+ IL H

IL H

H

H

HN

O

H

H2N

H2N

NH2NH2

NH2minusH2O

minusH2O










Acknowledgments


References













































Acknowledgments


References

























































Documents

H Functionalized Ionic Liquid Based on DABCO: New and Efficient