untitled European Journal of Chemistry 2 (2) (2011) 168‐172 European Journal of Chemistry ISSN 2153‐2249 (Print) / ISSN 2153‐2257 (Online)  2011 EURJCHEM DOI:10.5155/eurjchem.2.2.168‐172.228 European Journal of Chemistry Journal homepage: www.eurjchem.com Green methodologies in organic synthesis: Microwave assisted solvent‐ and catalyst‐free synthesis of enaminones and their conversion into 1,3,5‐trisubstituted benzenes as well as 3‐aroyl‐6‐substituted pyridines Morsy Ahmed El‐Apaserya,b, Saleh Mohamed Al‐Mousawia,* and Mohamed Helmy Elnagdia a Department of Chemistry, Faculty of Science, Kuwait University, Safat, 13060, Kuwait b Dyeing, Printing and Textile Auxiliaries Department, Textile Research Division, National Research Centre, Dokki, Giza, 12622, Egypt *Corresponding author at: Department of Chemistry, Faculty of Science, Kuwait University, Safat, 13060, Kuwait. Tel.: +96599728120; fax: +96524816482. E‐mail address: saleh.almousawi@yahoo.com (S.M. Al‐Mousawi). ARTICLE INFORMATION ABSTRACT Received: 03 August 2010 Received in revised form: 24 September 2010 Accepted: 16 November 2010 Online: 30 June 2011 KEYWORDS Enaminones were obtained in good yields via condensing methyl ketones with (N,N‐ dimethylformamide dimethyl acetal) DMF‐DMA under microwave irradiation in absence of solvent. These enaminones were readily converted into 1,3,5‐trisubstituted benzenes. Reacting enaminones in presence of ammonium acetate has afforded pyridine derivatives. Enaminone Solvent‐free Green chemistry Dye intermediates Microwave irradiation 1,3,5‐trisubstituted benzenes 1. Introduction Enaminones are polydentate reagents that are finding plenty of neat utilities in synthetic organic chemistry [1‐4] and/or dye intermediates [5‐7]. Microwave irradiation has been frequently used in diverse organic transformations with a remarkable reduction in reaction times and, in many cases, improving the yields and selectivity of the processes. We have already previously reported on the utility of enaminones as precursors to polyfunctional aromatics and heteroaromatics [8,9]. Enaminones are obtained via condensing methyl ketones with DMF‐DMA, through pathways employed benzene as solvent for this condensation. However several authors have reported that yields are quite low according to this protocol [10]. Domestic microwave irradiation has already been described in the preparation of enaminones by Braibante et al. [11,12] and by Hamelin et al. [13], in both cases, either a solid support or an acid catalyst was employed as reaction promoter. Lee et al. [14] reported a solvent‐free microwave assisted preparation of enaminones in a microwave (MW) reactor, using catalytic HCl and an excess of the amines. Synthesis of enaminones in absence of solvent has been reported in domestic microwave oven to afford better yield, shorter reaction times [15], but under such conditions productions of hazardous vapours could not be avoided. In the present article, we report high yield synthesis of enaminones 2a‐c via reacting 1a‐c with DMF‐DMA in a direct beam microwave reactor and report on conversion of the obtained enaminones as precursors for the title compounds which were needed in connection with a biological chemically programme in our laboratories. 2. Experimental 2.1. Instrumentation Melting points are uncorrected. All the reactions were conducted under microwave irradiation in heavy‐walled Pyrex tubes (capacity 10 mL). Microwave heating was carried out with a single mode cavity Explorer Microwave Synthesizer (CEM Corporation, NC, USA), producing continuous irradiation and equipped with simultaneous external air‐cooling system. IR spectra were recorded in KBr disks using a Perkin‐Elmer System 2000 FT‐IR spectrophoto‐meter. 1H NMR (400 MHz) and 13C NMR (100 MHz) spectra were recorded on a Bruker DPX 400, super‐conducting NMR spectrometer in CDCl3 or DMSO‐d6 as solvent and TMS as internal standard; chemical shifts were reported in  units (ppm). X‐ray crystallography was carried out on a Kappa CCD Enraf Nonius FR 590 diffractometer, National Research Center, Dokki, Giza, Egypt (Table 1). Mass spectra were measured on a VG Autospec‐Q (high resolution, high performance, tri‐sector GC/MS/MS). Microanalyses were performed on a LECO CHNS‐932 Elemental Analyzer. 2.2. Synthesis and purification of compounds (2a‐c) and (3) A mixtures of phthalimidoacetone (1a) or 2‐acetylpyrrole (1b) or acetophenone (1c) (0.01 mol) and DMF‐DMA (1.19 g, 0.01 mol) were irradiated by focused microwave at 180 °C for 20 min for product 2a, 120 °C for 10 min for product 2b, and 120 °C for 30 min for product 2c. Completion of the reactions was monitored by TLC. The build‐up of pressure in the closed El‐Apasery et al. / European Journal of Chemistry 2 (2) (2011) 168‐172 169 reaction vessel was carefully monitored. After the irradiation, the reaction tube was cooled with high‐pressure air through an inbuilt system in the instrument until the temperature had fallen below 50 °C. The reaction mixture left to cool to room temperature and then treated with a mixture of EtOH:dioxane (3:1). The solid product, so formed, was collected by filtration and crystallized from dioxane to afford compounds 2a‐c. The filtrate of product 2a was dried over anhydrous sodium sulphate and concentrated on vacuum. The residue was purified by column chromatography on silica gel with ethyl acetate:EtOH (9:1) as then eluent to afford product 3 in 10 % yields. 2‐(4‐Dimethylamino‐2‐oxo‐but‐3‐enyl)isoindole‐1,3‐dione, 2a: Yellow crystals. Yield: 77%. M.p.: 162 °C (Lit. 159‐162 °C [16]). FT‐IR (KBr, cm‐1): 1769, 1714, 1660 (CO). 1H NMR (400 MHz, DMSO‐d6): 2.72 (s, 3H, CH3), 3.05 (s, 3H, CH3), 4.40 (s, 2H, CH2), 5.04 (d, 1H, J=12 Hz, CH), 7.61 (d, 1H, J=12 Hz, CH), 7.85‐ 7.91 (m, 4H, phthalimidyl‐H). MS (EI, m/z, %): 258 [M+, 24%]. Anal. Calcd. for C14H14N2O3: C, 65.11; H, 5.46; N, 10.85. Found: C, 65.18; H, 5.44; N, 10.76. 3‐Dimethylamino‐1‐(1H‐pyrrol‐2‐yl)‐propenone, 2b: Orange crystals. Yield: 86%. M.p.: 199‐200 °C. FT‐IR (KBr, cm‐1): 3252 (NH), 1625 (CO). 1H NMR (400 MHz, DMSO‐d6): 2.88 (s, 3H, CH3), 3.03 (s, 3H, CH3), 5.62 (d, 1H, J=12.4 Hz, CH), 6.08‐6.10 (m, 1H, pyrrolyl‐H), 6.76‐6.78 (m, 1H, pyrrolyl‐H), 6.86‐6.88 (m, 1H, pyrrolyl‐H), 7.68 (d, 1H, J=12.4 Hz, CH), 11.41 (s, 1H, NH). MS (EI, m/z, %): 164 [M+, 100%]. Anal. Calcd. for C9H12N2O: C, 65.83; H, 7.37; N, 17.06. Found: C, 65.82; H, 7.91; N, 17.06. 3‐Dimethylamino‐1‐phenyl‐propenone, 2c: Orange crystals. Yield: 87%. FT‐IR (KBr, cm‐1): 1639 (CO). 1H NMR (400 MHz, DMSO‐d6): 2.90 (s, 3H, CH3), 3.14 (s, 3H, CH3), 5.81 (d, 1H, J=12.4 Hz, CH), 7.41‐7.50 (m, 3H, phenyl‐H), 7.70 (d, 1H, J=12.4 Hz, CH), 7.88‐7.90 (m, 2H, phenyl‐H). MS (EI, m/z, %): 175 [M+, 89%]. 2‐(1‐Dimethylaminomethylene‐2‐oxo‐propyl)isoindole‐1,3‐ dione, 3: Light yellow crystals. Yield: 15%. M.p.: 176‐178 °C. FT‐ IR (KBr, cm‐1): 1771, 1715, 1653 (CO). 1H NMR (400 MHz, CDCl3): 2.91 (s, 3H, CH3), 2.98 (s, 3H, NCH3), 3.22 (s, 3H, NCH3), 7.72‐7.75 (m, 2H, phthalimidyl‐H), 7.79 (s, 1H, CH), 7.87‐7.90 (m, 2H, phthalimidyl‐H). MS (EI, m/z, %): 258 [M+, 8%]. Anal. Calcd. for C14H14N2O3: C, 65.11; H, 5.46; N, 10.85. Found: C, 65.01; H, 5.61; N, 11.05. 2.3. Synthesis of compounds (6a,b) 2.3.1. 2‐(2‐3,5‐Di[2‐(1,3‐dioxo‐2,3‐dihydro‐1H‐2‐isoindolyl) acetyl]phenyl‐2‐oxoethyl)‐1,3‐isoindolinedione (6a) A mixture of compound 2a (2.58 g, 0.01 mol), indium chloride (0.02 g) and acetic acid (0.5 mL) was irradiated in microwave at 140 oC for 30 min. The crude product was poured onto water, the solid product, so formed, was collected by filtration and crystallized from toluene. Light brown. Yield: 58 %. M.p.: 300‐301 oC. FT‐IR (KBr, cm‐1): 1776, 1721 (CO). 1H NMR (400 MHz, DMSO‐d6): 5.57 (s, 6H, CH2), 7.93‐7.99 (m‐12H, phthal‐imidyl‐H), 8.98 (s, 3H, benzyl‐H). 13C NMR (DMSO‐d6): 192.23, 167.98 (2 CO), 135.33, 135.20, 133.39, 132.02, 123.93, 45.50 (CH2). MS (EI, m/z, %): 639 [M+, 12%]. Anal. Calcd. for C36H21 N3O9: C, 67.61; H, 3.31; N, 6.57. Found 67.46; H, 3.33; N, 6.81. 2.3.2. [3,5‐di(1H‐2‐pyrrolylcarbonyl)phenyl](1H‐2‐pyrrolyl) methanone (6b) A mixture of compound 2b (1.64 g, 0.01 mol) and acetic acid (0.5 mL) was irradiated by focused microwave at 140 °C for 30 min. Completion of reaction was monitored by TLC. The solid product, so formed, was collected and crystallized from dioxane to afford compounds 6b. Yield 93%. M.p.: 259‐260 °C. FT‐IR (KBr, cm‐1): 3290 (NH), 1626 (CO). 1H NMR (400 MHz, DMSO‐d6): 6.130‐6.30 (m, 1H, pyrrolyl‐H), 6.91‐6.93 (m, 1H, pyrrolyl‐H), 7.28‐7.30 (m, 1H, pyrrolyl‐H), 8.37 (s, 1H, benzoyl‐ H), 12.22 (s, 1H, NH). 13C NMR (DMSO‐d6, 100 MHz): 182.10 (CO), 138.84, 131.21, 130.17, 127.20, 119.81, 110.69. MS (EI, m/z, %): 357 [M+, 100%]. Anal. Calcd. for C21H15N3O3: C, 70.58; H, 4.23; N, 11.76. Found: C, 69.77; H, 4.74; N, 11.30. 2.4. General procedure for the synthesis of compounds (8a,b) A mixture of compound 2a (0.02 mol), 2b or 2c (0.1 mol) and acetic acid (0.5 mL) was irradiated by focused microwave at 140 °C for 30 min. The solid product, so formed, was collected and crystallized from dioxane to afford compounds 8a,b. 2‐2‐[3‐[2‐(1,3‐dioxo‐2,3‐dihydro‐1H‐2‐isoindolyl)acetyl]‐5‐ (1H‐2‐pyrrolylcarbony)phenyl]‐2‐oxoethyl‐1,3‐isoindolinedione, 8a: Buff powder. Yield: 52%. M.p.: 252‐253 °C. FT‐IR (KBr, cm‐ 1): 3343 (NH), 1717 (CO). 1H NMR (400 MHz, DMSO‐d6): 5.54 (d, 4H, J=12.4 Hz, 2NCH2), 6.23‐6.33 (m, 1H, pyrrolyl‐H), 6.93‐ 6.96 (m, 1H, pyrrolyl‐H), 7.31‐7.33 (m, 1H, pyrrolyl‐H), 7.91‐ 7.95 (m, 4H, Ar‐H), 7.98‐8.00 (m, 4H, Ar‐H), 8.62 (d, 1H, J=1.2 Hz, CH), 8.98 (s, 1H, CH), 12.29 (s, 1H, NH). MS (EI, m/z, %): 545 [M+, 18%]. Anal. Calcd. for C31H19N3O7: C, 68.26; H, 3.51; N, 7.70. Found: 68.37; H, 3.91; N, 7.74. 2‐(2‐3‐benzoyl‐5‐[2‐(1,3‐dioxo‐2,3‐dihydro‐1H‐2‐isoindolyl) acetyl]phenyl‐2‐oxoethyl)‐1,3‐isoindolinedione, 8b: Brown powder. Yield: 68%. M.p.: 194‐496 °C. FT‐IR (KBr, cm‐1): 1718 (CO). 1H NMR (400 MHz, DMSO‐d6): 5.55 (d, 4H, J=7.6 Hz, 2NCH2), 7.30‐732 (m, 3H, Ar‐H), 7.56‐7.59 (m, 2H, Ar‐H), 7.83‐ 7.87 (m, 4H, Ar‐H), 7.93‐7.98 (m, 4H, Ar‐H), 8.57 (s, 1H, CH), 8.98 (s, 1H, CH). MS (EI, m/z, %): 556 [M+, 32%]. Anal. Calcd. for C33H20N2O7: C, 71.22; H, 3.62; N, 5.03. Found: C, 70.94; H, 3.96; N, 5.72. 2.5. General procedure for the synthesis of compounds (9a‐c) A mixture of compounds 2a‐c (0.01 mol), EtOH (1 mL) and aniline (0.93g, 0.01 mol) were irradiated by focused microwave at 140 °C for 5 min. The reaction mixture was poured into cold water, filtered and crystallized from ethanol to afford compounds 9a‐c. 2‐(2‐Oxo‐4‐phenylamino‐but‐3‐enyl)isoindole‐1,3‐dione, 9a: Yellow‐orange crystals. Yield: 88%. M.p.: 167‐169 °C. FT‐IR (KBr, cm‐1): 3457 (NH), 1773, 1706, 1640 (CO). 1H NMR (400 MHz, DMSO‐d6): 4.50 (s, 2H, NCH2), 5.45 (d, 1H, J=8.0 Hz, CH), 7.03 (t, 1H, J=7.2 Hz, phenyl‐H), 7.25 (d, 2H, J=8.0 Hz, phenyl‐H), 7.30 (t, 2H, J=7.2 Hz, phenyl‐H), 7.77 (dd, 1H, J=8.0 Hz, J=8.0 Hz CH), 7.87‐7.90 (m, 2H, phthalimidyl‐H), 7.91‐7.95 (m, 2H, phthalimidyl‐H), 11.15 (d, 1H, J=12.6 Hz, NH). 13C NMR (DMSO‐ d6, 100 MHz): 191.47, 168.22 (CO), 145.75, 140.38, 135.16, 132.14, 130.06, 123.96, 123.69, 116.66, 93.58, 45.79 (NCH2). MS (EI, m/z, %): 306 [M+, 20%]; 160 (25), 146 (100), 117 (8), 104 (14), 77 (12). Anal. Calcd. for C18H14N2O3: C, 70.58; H, 4.61, N, 9.15. Found: C, 70.55; H, 4.61, N, 9.27. 3‐Phenylamino‐1‐(1H‐pyrrol‐2‐yl)‐propenone, 9b: Golden‐ yellow crystals. Yield: 74%. M.p.: 217‐218 °C. FT‐IR (KBr, cm‐1): 3262 (NH), 1635 (CO). 1H NMR (400 MHz, DMSO‐d6): 5.85 (d,1H, J=8.0 Hz, CH), 6.16‐6.18 (m, 1H, pyrrolyl‐H), 6.88‐6.90 (m, 1H, pyrrolyl‐H), 7.00‐7.04 (m, 1H, pyrrolyl‐H), 7.21 (d,2H, J=8.4 Hz, phenyl‐H), 7.32 (t, 3H, J=8.4 Hz, phenyl‐H), 7.69 (dd, 1H, J=8.0 Hz, J=8.0 Hz, CH), 11.63 (s, 1H, NH), 11.71 (s, 1H, NH). MS (EI, m/z, %): 212 [M+, 100%]. Anal. Calcd. for C13H12N2O: C, 73.56; H, 5.70; N, 13.20. Found: C, 73.42; H, 6.03; N, 13.07. 1‐Phenyl‐3‐phenylamino‐propenone, 9c: Yellow crystals. Yield: 83%. All data agreed with the published one [17]. 170 El‐Apasery et al. / European Journal of Chemistry 2 (2) (2011) 168‐172 Table 1. Crystal data and structure refinement for compound 3. Chemical formula C14H14N2O3 Formula weight 258.277 Crystal System Triclinic Space group P‐1 a 7.9478 (5) Å b 8.4931 (6) Å c 11.1333 (8) Å  88.231 (2)   83.557 (2)   62.615 (2)  V 662.90 (8) Å3 Z 2 Temperature 298 K Radiation type Mo K Measured reflections 3228 Independent reflections 2435 Observed reflections 1252 Rint 0.036 R(all) 0.111 R(gt) 0.064 wR(ref) 0.119 wR(all) 0.126 Parameters 172 2.6. General procedure for the synthesis of compounds (12a,b) A mixture of compound 2a‐b (0.01 mol) and ammonium acetate (0.2 mol) was irradiated by focused microwave at 160 °C for 10 min for product 12a, 140 °C for 10 min for product 12b. Completion of reaction was monitored by TLC. The solid product, so formed, was collected and crystallized from dioxane:EtOH (1:3) to afford compounds 12a,b. 2‐(5‐[2‐(1,3‐dioxo‐2,3‐dihydro‐1H‐2‐isoindolyl)acetyl]‐2‐ pyridylmethyl)‐1,3‐isoindolinedione, 12a: Buff powder. Yield: 53%. M.p.: 235‐236 °C. FT‐IR (KBr, cm‐1): 1714 (CO). 1H NMR (400 MHz, DMSO‐d6): 5.04 (s, 2H, CH2), 5.29 (s, 2H, CH2), 7.23 (d, 1H, J=7.6 Hz, Ar‐H), 7.59‐7.63 (m, 1H, Ar‐H), 7.31 (d, 1H, J=8.4 Hz, Ar‐H), 7.76‐7.81 (m, 1H, Ar‐H). 7.87 (s, 1H, Ar‐H), 7.98‐8.00 (m, 4H, Ar‐H), 7.31 (dd, 1H, J=2.4 Hz, J=2.0 Hz, Ar‐H), 9.15 (s, 1H, Ar‐H). MS (EI, m/z, %): 425 [M+, 10%]. Anal. Calcd. for C24H15N3O5: C, 67.76; H, 3.55; N, 9.88. Found: C, 67.70; H, 3.63; N, 9.77. 1H‐2‐pyrrolyl[6‐(1H‐2‐pyrrolyl)‐3‐pyridyl]methanone, 12b: Brown powder. Yield: 78%. M.p.: 136‐137 °C. FT‐IR (KBr, cm‐1): 3295 (NH), 1618 (CO). 1H NMR (400 MHz, DMSO‐d6): 6.31 (t, 1H, J=4.0 Hz, pyrrolyl‐H), 6.92 (t, 1H, J=2.8 Hz, pyrrolyl‐H), 7.30 (d, 1H, J=9.2 Hz, pyrrolyl‐H), 8.41(d, 2H, J=4.8 Hz, pyridinyl‐H), 9.14 (s, 1H, pyridinyl‐H), 12.28 (s, 2H, NH). MS (EI, m/z, %): 237 [M+, 100%]. Anal. Calcd. for C14H11N3O: C, 70.87; H, 4.67; N, 17.71. Found: C, 69.87; H, 4.66; N, 17.53. 3. Results and discussion Condensation of phthalimidoacetone 1a with dimethyl formamide dimethyl acetal (DMF‐DMA) has afforded enaminone 2a in focused microwave oven at 180 °C for 20 min in absence of solvent in 77 % yield. Also, a side product was isolated from this reaction. Isolation of the side product has not been observed earlier. The X‐ray crystal structure for this product indicated that it resulted from condensation of methylene moiety in 1a with DMF‐DMA to yield 2‐(1‐ dimethylamino methylene‐2‐oxo‐propyl)isoindole‐1,3‐dione (3) (Figure 1). In Table 2, we list the selected bond lengths and angles for compound 3. It is clear from Figure 1 that the product adopted sterical strained form compound 3 rather than compound 3a. This is a further example indicating that steroelectronic factors overweight steric factors. It has previously indicated that this is the case when steroelectronic factors and steric factors contradict [18]. Bond length for N2‐C15 is typical for N‐C single bond. The same applies for N5 and C7 indicating that charge separated resonance form 3a does play significant role. Heating of methyl ketones 1b,c with (DMF‐DMA) in MW with solvent‐free at 120 °C for 10‐30 min has afforded enaminones 2b,c in 86% and 87% yields, respectively. Recently, it was reported that heating neat reactants in ionic liquid afforded compounds 2b,c in 86% and 70% yields, respectively [19] (Scheme 1). Figure 1. X‐ray crystal structure of compound (3). Table 2. Selected bond lengths and angles for compound 3. Bond Bond length (Å) Bond Bond angle (°) N2‐C6 1.397 (6) C7‐N5‐C17 120.0 (4) N2‐C13 1.414 (6) N2‐C15‐C7 123.5 (3) N2‐C15 1.434 (5) C7‐C15‐C9 121.8 (4) N5‐C7 1.339 (6) N5‐C7‐C15 33.3 (4) N5‐C17 1.453 (6) N2‐C15‐C9 114.7 (3) C7‐C15 1.349 (5) N2‐C15‐C7 123.5 (3) N5‐C18 1.448 (6) N5‐C7‐H7 120.3 (4) N5‐C7‐C15‐C9 ‐179.4 (7) Scheme 1 Compound 2b undergoes self‐condensation on heating in focused microwave at 140 oC for 30 min in presence of a few drops of acetic acid to give 1,3,5‐triacylbenzene 6b in 93% yields. We believe that compound 2b is initially converted to the open chain intermediate 4 that further adds to one molecule of enaminone 2b to yield the intermediate 5, which aromatize under these reaction conditions to give the final isolable product 6b. In a trial to enhance the polycondensation of 2a using InCl3 as catalyst the reaction resulted only in the formation of 6a, which has been recently reported by us [16] (Scheme 2). Compounds 2a‐c, have proved to be a versatile starting materials for a variety of otherwise not readily obtainable functionally substituted aromatics and heteroaromatics. Thus, heating a mixture of enaminones 2a with 2b or 2c as 2:1 ratio in focused microwave oven at 140 °C for 30 min in presence of few drops of acetic acid afforded products that were identified as 1,3,5‐trisubstituted benzenes 8a,b in 52% and 68% yields, respectively. It is most likely that the initial step in this reaction is addition of 2a to 2b or 2c to furnish an intermediate 7, which then reacts further with 2a to yield final isolable products 8a,b (Scheme 3). El‐Apasery et al. / European Journal of Chemistry 2 (2) (2011) 168‐172 171 Scheme 2 Scheme 3 Compound 2a‐c reacted with aniline in focused microwave oven at 140 ºC for 5 min afforded the aniline derivatives 9a‐c in 88%, 74% and 83% yields, respectively (Scheme 4). Heating enaminones 2a,b with ammonium acetate, in focused microwave oven at 160‐140 oC for 10 min afforded the 3‐aroyl‐6‐substituted pyridines 12a,b in 53% and 78% yields, respectively. Formation of 12a,b may take place through an initial self condensation of 2 to afford the intermediate 10 which reacts directly with ammonium ion to give a further intermediate 11, that undergoes intramolecular cycloconden‐ sation, via loss one molecule of water to give the final products (Scheme 5). 4. Conclusion The studies described above clearly demonstrate that an efficient method was achieved for the preparation of enaminones, employing green methodologies. The simplicity of the reaction conditions, their efficacy and excellent yields obtained using MW irradiation, under solvent‐ and catalyst‐free conditions. Also we could show that the enaminones 2a‐c is a valuable precursor to the triacylbenzene 1,3,5‐trisubstituted benzenes as well as 3‐aroyl‐6‐substituted pyridines. 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