{Facile and rapid synthesis of divers xanthene derivatives using lanthanum(III) chloride/chloroacetic acid as an efficient and reusable catalytic system under solvent-free conditions} J. Serb. Chem. Soc. 82 (5) 483–493 (2017) UDC 546.654’131+547.451.62–32+ JSCS–4982 547.815:542.913 Original scientific paper 483 Facile and rapid synthesis of diverse xanthene derivatives using lanthanum(III) chloride/chloroacetic acid as an efficient and reusable catalytic system under solvent-free conditions BEHJAT POURAMIRI, MARYAM SHIRVANI and ESMAT TAVAKOLINEJAD KERMANI* Department of Chemistry, Shahid Bahonar University of Kerman, Kerman 76169, Iran (Received 3 August 2016, revised 5 March, accepted 10 March 2017) Abstract: LaCl3/ClCH2COOH was used as an efficient, and recyclable catalytic system for synthesis of 11H-benzo[a]xanthene-11-one, hexahydro-1H-xan- thene-1,8(2H)-dione and 11-aryl-10H-diindeno[1,2-b:2′,1′-e]pyran-10,12(11H)- -dione derivatives via a one-pot three-component reaction of aldehydes, 2-naphthol, and cyclic 1,3-dicarbonyl compounds. The reactions proceeded rapidly at 70 °C under solvent-free conditions and the desired products were obtained in good to excellent yields. Keywords: multi-component reactions (MCRs); 11H-benzo[a]xanthene; hexa- hydro-1H-xanthene, 1,3-dicarbonyl compounds; solvent-free conditions; green chemistry. INTRODUCTION In the past few decades, heterocyclic chemistry has become one of the most important disciplines in organic synthesis and pharmaceutical chemistry.1 A large numbers of the synthesized compounds have emerged as active pharma- ceutical components in several drugs due to their potential anti-inflammatory,2,3 anti-tumor,4 anti-hyperlipidemic,5 anti-hypertensive,6 anti-HIV infections7 and several other biological properties.8,9 Xanthenes are an important class of heterocyclic compounds with remark- able biological and medicinal properties, such as antiviral, antibacterial and anti- -inflammatory activity.10–13 Furthermore, they are used as leuco-dyes, pH sen- sitive fluorescent materials, and in laser technologies.14–16 Among this class of molecules, xanthone is a prominent structural motif found in numerous natural products and synthetic compounds with important biological activities.17–21 Multi-component reactions (MCRs) have emerged as efficient and powerful tools in organic and medicinal chemistry due to their ability to synthesize organic * Corresponding author. E-mail: etavakoly@yahoo.com https://doi.org/10.2298/JSC160803034P _________________________________________________________________________________________________________________________ (CC) 2017 SCS. Available on line at www.shd.org.rs/JSCS/ 484 POURAMIRI, SHIRVANI and TAVAKOLINEJAD KERMANI molecules with higher efficiency and atom economy in a single step from three or more reactants. Moreover, MCRs offer the advantage of simplicity and syn- thetic efficiency over conventional chemical reactions.22 Therefore, developing new MCRs and improving known MCRs for the synthesis of diverse groups of compounds, especially ones that are biologically active, have gained great atten- tion in current organic synthesis.23–25 In addition, solvent-free conditions make synthesis simpler, save energy, and prevent solvent waste, hazards, and toxic- ity.26–28 It therefore remains a challenge to develop multi-component reactions with suitable heterogeneous catalysts. An interesting example of MCRs is the synthesis of xanthene derivatives that can be realized by condensation of aldehydes with β-naphthol, cyclic 1,3-dicar- bonyl compounds and/or a mixture of aldehyde and cyclic 1,3-dicarbonyl com- pounds. Various catalysts, such as KAl(SO4)2·12H2O,29 nano-SnCl4·SiO2,30 nano-ZnO,31 iodine,32 silica sulfuric acid33 and [Et3NSO3H]Cl34 have been used for the preparation of 14-aryl-14H-dibenzo[a,j]xanthenes. SbCl3/SiO2,35 SiO2– –RSO3H,36 p-dodecylbenzenesulfonic acid,37 triethylbenzylammonium chlor- ide38 and diammonium hydrogen phosphate39 have been used for the synthesis of 3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-diones octahydroxanthenes. Sulf- amic acid,40 dodecatungstophosphoric acid,41 InCl3/P2O542 and poly(2-acryl- amido-2-methylpropane sulphonic acid) crosslinked with N,N′-methylenebis- (acrylamide) (poly(AMPS-co-AA))43 have been used for the preparation of tetra- hydrobenzo[a]xanthen-11-ones. However, some of these methods involved long reaction times, harsh reaction conditions, or unsatisfactory yields. Therefore, improvements of these synthesis methods have been continuously sought. In continuation of ongoing research on green catalytic systems and their applications in organic synthesis and their applications as catalysts in organic synthesis,44–46 it was decided to investigate lanthanum(III) chloride/chloroacetic acid (LaCl3/ClCH2COOH) as a highly efficient, and reusable catalytic system for the practical, one-pot, three-component synthesis of 11H-benzo[a]xanthen-11- -ones, hexahydro-1H-xanthene-1,8(2H)-diones and 11-aryl-10H-diindeno[1,2- -b:2′,1′-e]pyran-10,12(11H)-diones under solvent-free conditions (Scheme 1). EXPERIMENTAL Chemicals and apparatus Chemicals were either laboratory-prepared or purchased from Merck or Fluka com- panies, and were used without any further purification. The IR spectra were recorded in KBr using a Bruker FT-IR spectrophotometer. The 1H- and 13C-NMR were recorded in CDCl3 and DMSO-d6 on a Bruker DRX-500 spectrometer using tetramethylsilane as an internal reference. The melting points were determined with a hot-plate microscope apparatus. The purity determination of the substrates and reaction monitoring were accomplished by TLC (petroleum ether (b.p.: 35‒60 °C)–ethyl acetate (b.p.: 77.1 °C), 3:1) on silica-gel POLYGRAM SIL G/UV254 plates (Merck). _________________________________________________________________________________________________________________________ (CC) 2017 SCS. Available on line at www.shd.org.rs/JSCS/ SYNTHESIS OF XANTHENE DERIVATIVES UNDER SOLVENT-FREE CONDITIONS 485 Scheme 1. One-pot synthesis of xanthene derivatives using LaCl3/ClCH2COOH as an efficient and reusable catalytic system. General procedure for the synthesis of 12-aryl-8,9,10,12-tetrahydro11H-benzo[a]xanthen-11- -ones (5) A mixture of aldehyde (1, 1 mmol), β-naphthol (3, 1 mmol), dimedone or 1,3-cyclohex- anedione (2, 1.2 mmol) and LaCl3/ClCH2COOH (10 mol %) was stirred in an oil-bath at 70 °C for a reasonable time. After completion of the reaction, as monitored by TLC, the reaction mixture was cooled, diluted with Et2O (5 mL) and filtered to remove catalyst. The crude product was recrystallized from ethanol to afford the pure product. General procedure for the synthesis of compounds 6 and 7 To a mixture of aromatic aldehyde (1, 1 mmol) and a cyclic 1,3-dicarbonyl compounds (2 or 4, 2 mmol), LaCl3/ClCH2COOH (10 mol %) was added and the mixture was heated on an oil bath at 70 °C for a reasonable time. After completion of the reaction, hot ethanol was added to the mixture and then filtered. The residue was recrystallized from ethanol. The spectral data of the synthesized compounds 5 and 6 are presented in the Supple- mentary material to this paper. RESULTS AND DISCUSSION Initially, to achieve suitable reaction conditions, the one-pot, three-compo- nent reaction of 2-naphthol, benzaldehyde, dimedone and LaCl3/ClCH2COOH as a model reaction was investigated. Subsequently efforts were focused on the optimization of various reaction parameters, such as amount of LaCl3/ /ClCH2COOH and temperature, in terms of yield and time. This observation rev- ealed that the use of 10 mol % LaCl3/ClCH2COOH at 70 °C under solvent-free _________________________________________________________________________________________________________________________ (CC) 2017 SCS. Available on line at www.shd.org.rs/JSCS/ 486 POURAMIRI, SHIRVANI and TAVAKOLINEJAD KERMANI conditions produced 9,9-dimethyl-12-phenyl-8,9,10,12-tetrahydro-11H-benzo[a]- xanthen-11-one (5a), after 10 min, in 96 % yield. Notably, the desired product could not be obtained under similar reaction conditions, even after a long time (1 h) in the absence of the catalyst (Table I). TABLE I. Screening of the reaction conditions for the synthesis of 9,9-dimethyl-12-phenyl- 8,9,10,12-tetrahydro-11H-benzo[a]xanthen-11-one (5a) Yielda, % Time, min Temperature, °C Amount LaCl3/ClCH2COOH, mol%Entry 0 60 70 No catalyst 1 20 35 50 LaCl3 (10 mol %) 2 25 30 60 LaCl3 (15 mol %) 3 35 50 70 ClCH2COOH (10 mol %) 4 40 55 80 ClCH2COOH (20 mol %) 5 70 25 70 LaCl3/ClCH2COOH (5 mol %) 6 85 20 60 LaCl3/ClCH2COOH (10 mol %) 7 96 10 70 LaCl3/ClCH2COOH (10 mol %) 8 96 10 80 LaCl3/ClCH2COOH (10 mol %) 9 aIsolated yields In order to study the generality of the procedure, three series of various xanthene derivatives having different steric and electronic properties were syn- thesized using the optimized conditions. In all cases, the corresponding products were obtained in good to excellent yields. The results are presented in Tables II and III. The obtained products were characterized by IR, 1H-NMR and 13C-NMR spectroscopy and physical data and the results were compared with the corresponding values for known xanthenes. TABLE II. One-pot preparation 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-ones M.p. / °C Yield, % Time, min Product R X Entry Reported Found 151–15342 152–150 96 10 CH3 H 5a _________________________________________________________________________________________________________________________ (CC) 2017 SCS. Available on line at www.shd.org.rs/JSCS/ SYNTHESIS OF XANTHENE DERIVATIVES UNDER SOLVENT-FREE CONDITIONS 487 TABLE II. Continued M.p. / °C Yield, % Time, min Product R X Entry Reported Found 209–21142 211–209 90 11 CH3 4-OH 5b 189–19047 191– 189 92 10 H H 5c 235–23647 238–233 97 10 H 3-NO25d 234–23547 234–236 92 10 H 4-NO25e 269–27047 267–270 93 10 H 4-OH 5f aIsolated yields In order to show the merit of the present work, the present results were compared with those reported by other groups in the synthesis of 9,9-dimethyl- 12-phenyl-8,9,10,12-tetrahydro-11H-benzo[a]xanthen-11-one (5a). It is import- ant to note that LaCl3/ClCH2COOH acts as an effective catalytic system with respect to reaction time and yield (Table IV). In a plausible mechanism, at first, the carbonyl group of the aromatic alde- hyde is activated through coordination with acidic LaCl3/ClCH2COOH to give 8. _________________________________________________________________________________________________________________________ (CC) 2017 SCS. Available on line at www.shd.org.rs/JSCS/ 488 POURAMIRI, SHIRVANI and TAVAKOLINEJAD KERMANI Next, the carbonyl carbon is attacked by the nucleophilic 1,3-dione derivative to form Knoevenagel products. The subsequent addition of these fragments to 2–4 gives the acyclic adduct intermediate, which undergoes intramolecular cyclization with participation of two hydroxyl groups to afford the xanthene derivatives (Scheme 2). TABLE III. One-pot preparation of hexahydro-1H-xanthene-1,8(2H)-dione and diindeno[1,2- -b:2′,1′-e]pyran-diones M.p. / °C Yield, % Time, min Product R1 X Entry Reported Found 201–20348 204–202 86 10 H H 6a 231–23348 232–230 92 10 H 4-Cl 6b 245–24748 246–243 97 10 H 4-OH 6c _________________________________________________________________________________________________________________________ (CC) 2017 SCS. Available on line at www.shd.org.rs/JSCS/ SYNTHESIS OF XANTHENE DERIVATIVES UNDER SOLVENT-FREE CONDITIONS 489 TABLE III. Continued M.p. / °C Yield, % Time, min Product R1 X Entry Reported Found 216–21848 217–219 92 10 H 4-CH36d 246–24843 245–248 93 8 H 4-NO26e 277–27943 236–240 96 7 H 3-NO26f 203–20449 202–204 90 8 CH3 H 6g 230–23249 230–233 93 9 CH3 4-Cl 6h 290–29150 288–290 80 10 – H 7a _________________________________________________________________________________________________________________________ (CC) 2017 SCS. Available on line at www.shd.org.rs/JSCS/ 490 POURAMIRI, SHIRVANI and TAVAKOLINEJAD KERMANI TABLE III. Continued m.p. / °C Yield, % Time, min Product R1 X Entry Reported Found – 310–312 85 9 – 4-Cl 7b aIsolated yields TABLE IV. Comparison of the results for the synthesis of xanthene 5a with different catalysts: DBSA, p-dodecylbenzenesulfonic acid; TBAHS, tetrabutylammonium hydrogen sulfate; experimental conditions: benzaldehyde (1 mmol), 2-naphthol (1 mmol), dimedone (1 mmol) and LaCl3/ClCH2COOH (10 mol %) Catalyst Catalyst load mol % Solvent Temp., °C Time, min Yielda % DBSA 10 H2O, ultrasound 30 60 8951 TMSCl 100 MeCN reflux 420 9552 HClO4–SiO2 10 Solvent-free 140 180 3253 SbCl3–SiO2 10 Solvent-free 120 50 9335 PPA–SiO2 10 Solvent-free 140 30 9353 TBAHS 10 Dioxane, H2O reflux 210 8854 LaCl3/ClCH2COOH 10 Solvent-free 70 10 96 aIsolated yields Scheme 2. The proposed mechanism for the synthesis of xanthene derivatives using LaCl3/ClCH2COOH. _________________________________________________________________________________________________________________________ (CC) 2017 SCS. Available on line at www.shd.org.rs/JSCS/ SYNTHESIS OF XANTHENE DERIVATIVES UNDER SOLVENT-FREE CONDITIONS 491 Finally, the possibility of recycling of LaCl3/ClCH2COOH was investigated using the model reaction forming 5a in the presence of LaCl3/ClCH2COOH. After completion of the reaction, ice-cold water was added to the reaction mix- ture and the product was filtered. After completely washing the solid product with water, the aqueous layer containing the catalytic system (LaCl3 and ClCH2COOH are soluble in water) was evaporated under reduced pressure and catalyst was recovered and reused for subsequent reactions. The recovered cat- alyst showed the same activity as that of the fresh catalyst without any loss of activity in terms of yield and product purity. The catalyst was recycled and reused in the same reaction at least four times with remarkable retention of its activity (Table V). TABLE V. Recycling yields (refer to pure isolated yields); reaction conditions: benzaldehyde (1 mmol), 2-naphthol (1 mmol), dimedone (1 mmol) and LaCl3/ClCH2COOH (10 mol %) No. of Cycles Fresh Run 1 Run 2 Run 3 Run 4 Yield, % 96 96 96 96 96 Time, min 10 10 10 10 10 CONCLUSIONS In conclusion, an efficient catalytic system was developed for the synthesis of various xanthene derivatives via one-pot three-component reactions of alde- hydes, 2-naphthol, and cyclic 1,3-dicarbonyl compounds. The advantages of the presented procedure include simplicity of operation, high yields of products, short reaction time and solvent-free conditions. SUPPLEMENTARY MATERIAL Analytical and spectral data of the synthesized compounds are available at the pages of the journal’s website: http://www.shd.org.rs/JSCS/, or from the corresponding author on request. Acknowledgement. We gratefully acknowledge the funding support received for this project from the Research Council of Shahid Bahonar University of Kerman. И З В О Д БРЗА СИНТЕЗА КСАНТЕНСКИХ ДЕРИВАТА УПОТРЕБОМ КАТАЛИТИЧКОГ СИСТЕМА ЛАНТАН(III)-ХЛОРИД/ХЛОРСИРЋЕТНА КИСЕЛИНА У ОДСУСТВУ РАСТВАРАЧА BEHJAT POURAMIRI, MARYAM SHIRVANI и ESMAT TAVAKOLINEJAD KERMANI Department of Chemistry, Shahid Bahonar University of Kerman, Kerman 76169, Iran LaCl3/ClCH2COOH је коришћен као ефикасан каталитички систем, који се успешно може поновно користити више пута после изоловања, за синтезу деривата 11H-бензо[a]- ксантен-11-она, хексахидро-1H-ксантен1,8(2H)-диона и 11-арил-10H-дииндено[1,2- -b:2′,1′-e]пиран-10,12(11H)-диона. Синтеза се врши у једном кораку, у трокомпонентној реакционој смеши алдехида, 2-нафтола, и цикличног 1,3-дикарбонилног једињења. _________________________________________________________________________________________________________________________ (CC) 2017 SCS. 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