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Synlett 2013; 24(17): 2241-2244
DOI: 10.1055/s-0033-1339758
letter
© Georg Thieme Verlag Stuttgart · New York

Samarium(III) Triflate as an Efficient and Reusable Catalyst for Facile Synthesis of Benzoxazoles and Benzothiazoles in Aqueous Medium

Pratapsinha B. Gorepatil
Department of Chemistry, S. C. S. College, Omerga, Dist-Osmanabad 413 606, India   Fax: +91(2475)252020   Email: gorepatilpratap1986@gmail.com   Email: Inglevilas71@yahoo.in
,
Yogesh D. Mane
Department of Chemistry, S. C. S. College, Omerga, Dist-Osmanabad 413 606, India   Fax: +91(2475)252020   Email: gorepatilpratap1986@gmail.com   Email: Inglevilas71@yahoo.in
,
Vilas S. Ingle*
Department of Chemistry, S. C. S. College, Omerga, Dist-Osmanabad 413 606, India   Fax: +91(2475)252020   Email: gorepatilpratap1986@gmail.com   Email: Inglevilas71@yahoo.in
› Author Affiliations
Further Information

Publication History

Received: 16 June 2013

Accepted after revision: 18 August 2013

Publication Date:
13 September 2013 (online)

 
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Abstract

A simple, green, and efficient method is presented for the synthesis of benzoxazoles and benzothiazoles from reaction of o-aminophenols, o-aminothiophenols, and aliphatic or aromatic aldehydes using samarium triflate as a reusable acid catalyst under mild reaction conditions in aqueous medium.


#

Key words

benzoxazoles - benzothiazoles - samarium triflate

Benzoxazoles and benzothiazoles have attracted considerable attention due to their biological properties.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] The most commonly used synthetic approach involves condensation of o-aminothiophenols or o-aminophenols with aldehydes,[9] [11] although carboxylic acids,[12] alcohols,[13] and acid chlorides[14] have been utilized. However, most of the traditional synthetic methods suffer from drawbacks such as the need for strongly acidic conditions and high temperatures,[15a] [b] [c] [d] long reaction times,[15e] [f] and significant amounts of catalyst or toxic solvents.[15g] [h] Heterogeneous Lewis acid catalysis has attracted considerable attention[16] but, although a wide range of Lewis acids has been developed, most of them are used only under strictly anhydrous conditions.[17] Recently, with the objective of developing environmentally benign reaction conditions and media for organic reactions with excellent efficiency and selectivity, water has been shown to be a useful solvent for certain Lewis acids.[18] For instance, In(OTf)3, Yb(OTf)3, Bi(OTf)3, Sc(OTf)3, Sm(OTf)3, and other metal triflates have been found to be water-tolerant, reusable Lewis acids catalysts and have received considerable interest for condensation reactions[17] [19] and other organic transformations.[20] [21] [22]

In continuation of our interest in the synthesis of fused heterocyclic compounds,[23] we report herein the use of samarium triflate[24] as a water-tolerant Lewis acid catalyst for the synthesis of 2-substituted benzoxazoles and benzothiazoles by the condensation of o-aminophenols or o-aminothiophenols with aldehydes in aqueous ethanol as shown in Scheme [1].

Initially, the samarium triflate catalyzed reaction between equimolar quantities of o-aminophenol and benzaldehyde was selected as a model reaction for optimization under different concentrations and using different solvents as summarized in Table [1]. Samarium triflate (10 mol%) was found to be best suited for reaction in an ethanol–water (2:2) mixture at 60 °C compared to solvents such MeCN, dioxane, or toluene (Table [1], entry 7).

Zoom Image
Scheme 1 Samarium triflate [Sm(OTf)3] catalyzed synthesis of ­2-substituted benzoxazoles and benzothiazoles

Table 1 Optimization of Reaction Conditions for the Synthesis of 2-Phenylbenzoxazolea

Entry

Catalyst (mol%)

Solvent

Time (h)

Yield (%)b

 1

–

EtOH

12

25

 2

ZnO (5)

EtOH–H2O (2:2)

 5

45

 3

In2O3 (5)

EtOH–H2O (2:2)

 5

67

 4

Sm(OTf)3 (5)

EtOH

 2

62

 5

Sm(OTf)3 (2)

EtOH–H2O (2:2)

 6

76

 6

Sm(OTf)3 (5)

EtOH–H2O (2:2)

 2

85

 7

Sm(OTf)3 (10)

EtOH–H2O (2:2)

 2

92

 8

Sm(OTf)3 (5)

MeCN

 5

53

 9

Sm(OTf)3 (5)

dioxane

 5

57

10

Sm(OTf)3 (5)

toluene

 5

60

11

Sm(OTf)3 (10)

toluene

 5

82

a Stirring at 50–60 °C.

b Isolated yield.

After optimization, we extended the study to various o-aminophenols and o-aminothiophenols with a range of aliphatic, aromatic, and heteroaromatic aldehydes. In general, most of reactions proceeded very smoothly to give the corresponding 2-substituted benzoxazoles and benzothizoles in moderate to excellent yields and aldehydes containing a range of sensitive functional groups were acceptable under these conditions. As a general trend, electron-deficient aldehydes gave better yields in shorter reaction times as compared to electron-rich aldehydes (Table [2]).

Table 2 Sm(OTf)3-Catalyzed Synthesis of 2-Substituted Benzoxazoles and Benzothiazolesa

Entry

Aldehyde

Product

Time (h)

Yield (%)b

 1

2

92

 2

3

94

 3

4

85

 4

3.5

96

 5

4

95

 6

3.5

82

 7

4.5

74

 8

3

89

 9

2

89

10

4

75

11

3.5

92

12

4

94

13

5

72

14

4.5

87

15

3.5

82

16

6

78

a Reaction conditions: aldehyde (1 mmol), o-aminophenol/o-aminothiophenol (1 mmol), Sm(OTf)3 (10 mol%), EtOH–H2O (4:2 mL), stirring at 50–60 °C.

b Isolated yield.

After completion of the reaction, the catalyst was removed by simple filtration and washed with ethanol. The catalyst was then dried at 100 °C for one hour and could be reused. It was found that the catalytic activities of the recovered catalyst were almost the same as that of fresh catalyst over several runs (Table [3]).

Table 3 Catalyst Reusability Study for the Reaction of Benzaldehyde with o-Aminophenola

Entry

Yield (%)b

Catalyst recovery (%)

1

92

94

2

90

92

3

88

90

4

86

88

a Reaction conditions: benzaldehyde (1 mmol), o-aminophenol (1 mmol), Sm(OTf)3 (10 mol%), EtOH–H2O (2:2 mL), 50–60 °C.

b Isolated yield.

In conclusion, a simple and efficient method has been developed for the synthesis of 2-substituted benzoxazoles and benzothiazoles by using samarium triflate as a water-tolerant, recyclable Lewis acid catalyst in aqueous ethanol.


#

Acknowledgment

One of the authors, Mr. P.B. Gorepatil, is grateful to the CSIR-New Delhi for a Junior Research Fellowship (JRF).

  • References and Notes

    • 4a Huang W, Yang G.-F. Bioorg. Med. Chem. 2006; 14: 8280
      CrossrefSearch in Google Scholar
    • 4b Sheng C, Che X, Wang W, Wang S, Cao Y, Yao J, Miao Z, Zhang W. Eur. J. Med. Chem. 2011; 1706
    • 5a Patel P, Pillai J, Darji N, Patel B. Int. J. Drug Res. Technol. 2012; 2: 170
      Search in Google Scholar
    • 5b Shafi S, Alam MM, Mulakayala N, Mulakayala C, Vanaja G, Kalle AM, Pallu R, Alam MS. Eur. J. Med. Chem. 2012; 324
    • 6a Saeed S, Rashid N, Jones PG, Ali M, Hussain R. Eur. J. Med. Chem. 2010; 1323
    • 6b Bondock S, Fadaly W, Metwally MA. Eur. J. Med. Chem. 2009; 4813
  • 7 Nagarajan SR, De Crescenzo GA, Getman DP, Lu H.-F, Sikorski JA, Walker JL, McDonald JJ, Houseman KA, Kocan GP, Kishore N, Mehta PP, Funkes-Shippy CL, Blystone L. Bioorg. Med. Chem. 2003; 11: 4769
    CrossrefSearch in Google Scholar
  • 9 Bahrami K, Khodaei MM, Naali F. J. Org. Chem. 2008; 73: 6835
    CrossrefPubMedSearch in Google Scholar
  • 10 Sun Y, Duan L, Wei P, Qiao J, Dong G, Wang L, Qiu Y. Org. Lett. 2009; 11: 2069
    CrossrefSearch in Google Scholar
  • 13 Raghavendra GM, Ramesha AB, Revanna CN, Nandeesh KN, Mantelingu K, Rangappa KS. Tetrahedron Lett. 2011; 52: 5571
    CrossrefSearch in Google Scholar
    • 15a Kumar R, Selvam C, Kaur G, Chakraborti AK. Synlett 2005; 1401
      Thieme Connect
    • 15b Seijas JA, Vazquez-Tato MP, Carballido-Reboredo MR, Crecente Campo J, Romar-Lopez L. Synlett 2007; 313
    • 15c Ertan T, Yildiz I, Tekiner-Gulbas B, Bolelli K, Temiz-Arpaci O, Ozkan S, Kaynak F, Yalcin I, Aki E. Eur. J. Med. Chem. 2009; 501
    • 15d Terashima M, Ishii M, Kanaoka Y. Synthesis 1982; 484
      Thieme Connect
    • 15e Hein DW, Alheim RJ, Leavitt JJ. J. Am. Chem. Soc. 1957; 79: 427
      CrossrefSearch in Google Scholar
    • 15f So YH, Heeschen JP. J. Org. Chem. 1997; 62: 3552
      CrossrefSearch in Google Scholar
    • 15g Riadi Y, Mamouni R, Azzalou R, Haddad ME, Routier S, Guillaumet G, Lazar S. Tetrahedron Lett. 2011; 52: 3492
      CrossrefSearch in Google Scholar
    • 15h Tomoki Y, Hayato T, Tetsuya S, Masahiro M. Tetrahedron Lett. 2008; 49: 1598
      CrossrefSearch in Google Scholar
  • 16 Corma A, Garcia H. Chem. Rev. 2003; 103: 4307
    CrossrefPubMedSearch in Google Scholar
  • 17 Trivedi R, De SK, Gibbs RA. J. Mol. Catal. A: Chem. 2008; 245: 8
    Search in Google Scholar
  • 18 Li C.-J, Trost BM. Proc. Natl. Acad. Sci. U.S.A. 2008; 105: 13197
    CrossrefPubMedSearch in Google Scholar
  • 23 Gorepatil PB, Mane YD, Surywanshi VS, Shinde VS, Ingle VS. J. Curr. Chem. Pharm. Sci. 2012; 2: 367
    Search in Google Scholar
  • 24 General Procedure To a mixture of the requisite o-aminophenol/o-amino-thiophenol (1 mmol) and aldehyde (1 mmol) in EtOH–H2O (2:2 mL), samarium triflate catalyst (10 mol%) was added, and the resulting mixture was stirred at 60 °C. After completion of the reaction, as monitored by TLC, the mixture was diluted with H2O–EtOAc (1:1, 10 mL) and catalyst recovered by filtration. The filtrate was extracted with Et2O (2 × 10 mL) and dried with anhydrous Na2SO4. After filtration and evaporation of solvent, the crude product was recrystallized from EtOAc or MeOH. All the structures were confirmed by their analytical data and comparison with literature data.25–30 Spectroscopic Data for Selected Compounds 2-Phenylbenzo[d]oxazole (Table 2 Entry 1) Mp 100–102 °C. 1H NMR (300 MHz, DMSO-d 6): δ = 7.39 (m, 2 H), 7.57 (m, 3 H), 7.64 (m, 1 H), 7.80 (m, 1 H), 8.29 (m, 2 H). 13C NMR (75 MHz, DMSO-d 6): δ = 110.6, 119.9, 124.5, 125.1, 127.3, 127.5, 128.9, 131.5, 142.2, 150.8, 163.0. IR (KBr): 740, 1171, 1355, 1511, 1640, 3100 cm–1. MS (EI): m/z = 195.1 [M+]. 2-(4-Methylphenyl)benzo[d]oxazole (Table 2 Entry 3) Mp 114–116 °C. 1H NMR (300 MHz, DMSO-d 6): δ = 2.45 (s, 3 H), 7.36 (d, 2 H, J = 8.1 Hz), 7.41 (t, 1 H, J = 8.4 Hz), 7.51 (t, 1 H, J = 8.4 Hz), 7.96 (d, 1 H, J = 8.0 Hz), 8.00–8.06 (m, 3 H). 13C NMR (75 MHz, DMSO-d 6): δ = 21.2, 121.6, 122.9, 125.0, 126.2, 127.3, 129.7, 131.0, 135.0, 141.6, 154.2, 168.0. IR (KBr): 760, 1186, 1409, 1590, 1621, 2968 cm–1. MS (EI): m/z = 209.07 [M+]. 2-(4-Chlorophenyl)benzo[d]oxazole (Table 2 Entry 4) Mp 147–149 °C. 1H NMR (300 MHz, DMSO-d 6): δ = 7.44 (t, 1 H, J = 7.6 Hz), 7.50–7.56 (m, 3 H), 7.98 (d, 1 H, J = 8.1 Hz), 8.05–8.09 (m, 3 H). 13C NMR (75 MHz, DMSO-d 6): δ = 121.7, 123.2, 125.4, 126.5, 128.7, 129.2, 132.2, 135.1, 136.8, 154.1, 166.5. IR (KBr): 775, 1175, 1371, 1640, 2980 cm–1. MS (EI): m/z = 229 [M+] and 231 [M + 2]. 2-(4-Nitrophenyl)benzo[d]thiazole (Table 2 Entry 11) Mp 225–227 °C. 1H NMR (300 MHz, DMSO-d 6): δ = 7.51 (t, 1 H, J = 7.5 Hz), 7.60 (t, 1 H, J = 7.6 Hz), 8.01 (d, 1 H, J = 7.8 Hz), 8.16 (d, 1 H, J = 8.1 Hz), 8.36 (q, 4 H, J = 9.4 Hz). 13C NMR (75 MHz, DMSO-d 6): δ = 121.9, 123.8, 124.4, 126.1, 126.8, 128.2, 135.6, 139.2, 149.0, 154.1, 165.0. IR (KBr): 807, 1169, 1370, 1556, 1690, 3056 cm–1. MS (EI): m/z = 256.0 [M+]. 2-(Pyridin-4-yl)benzo[d]thiazole (Table 2 Entry 14) Mp 130–132 °C. 1H NMR (300 MHz, DMSO-d 6): δ = 7.44–7.50 (m, 2 H), 7.57 (t, 1 H, J = 8.1 Hz), 8.01 (d, 1 H, J = 7.9 Hz), 8.13 (d, 1 H, J = 8.2 Hz), 8.40 (dt, 1 H, J = 8.0, 1.7 Hz), 8.73 (dd, 1 H, J = 4.8z, 1.7 Hz). 13C NMR (75 MHz, DMSO-d 6): δ = 121.8, 123.3, 123.8, 125.6, 129.6, 134.4, 135.1, 148.5, 154.0, 164.7. IR (KBr): 690, 1150, 1400, 1653, 2360, 2905 cm–1. MS (EI): m/z = 212.03 [M+]. 2-(4-Methoxyphenyl)benzo[d]thiazole (Table 2 Entry 15) Mp 122–124 °C. 1H NMR (300 MHz, DMSO-d 6): δ = 3.89 (s, 3 H), 7.02 (d, 2 H, J = 8.4 Hz), 7.39 (t, 1 H, J = 7.2 Hz), 7.51 (t, 1 H, J = 7.2 Hz), 7.94 (d, 1 H, J = 7.8 Hz), 8.06 (m, 3 H). 13C NMR (75 MHz, DMSO-d 6): δ = 55.4, 114.3, 121.6, 122.7, 124.8, 126.2, 126.4, 129.0, 135.0, 154.3, 162.0, 167.7. IR (KBr): 781, 1170, 1450, 1597, 1650, 3010 cm–1. MS (EI): m/z = 241 [M+].
  • 25 Ranjit S, Liu X. Chem. Eur. J. 2011; 17: 1105
    CrossrefSearch in Google Scholar
  • 26 Huang J, Chan J, Chen Y, Borths CJ, Baucom KD, Larsen RD, Faul MM. J. Am. Chem. Soc. 2010; 132: 3674
    CrossrefSearch in Google Scholar
  • 27 Devalla VR, Ethirajulu K. J. Chem. Soc. 1995; 1497
  • 28 Bougrin K, Loupy A, Soufiaoui M. Tetrahedron 1998; 54: 8055
    CrossrefSearch in Google Scholar
  • 29 Balaji SL, Umesh RP, Jyotirling RM, Ramrao AM. Bull. Korean Chem. Soc. 2010; 31: 2329
    CrossrefSearch in Google Scholar
  • 30 Shi D.-F, Bradshaw TD, Wrigley S, McCall CJ, Lelieveld P, Fichtner I, Stevens MF. G. J. Med. Chem. 1996; 39: 3375
    CrossrefSearch in Google Scholar

  • References and Notes

    • 4a Huang W, Yang G.-F. Bioorg. Med. Chem. 2006; 14: 8280
      CrossrefSearch in Google Scholar
    • 4b Sheng C, Che X, Wang W, Wang S, Cao Y, Yao J, Miao Z, Zhang W. Eur. J. Med. Chem. 2011; 1706
    • 5a Patel P, Pillai J, Darji N, Patel B. Int. J. Drug Res. Technol. 2012; 2: 170
      Search in Google Scholar
    • 5b Shafi S, Alam MM, Mulakayala N, Mulakayala C, Vanaja G, Kalle AM, Pallu R, Alam MS. Eur. J. Med. Chem. 2012; 324
    • 6a Saeed S, Rashid N, Jones PG, Ali M, Hussain R. Eur. J. Med. Chem. 2010; 1323
    • 6b Bondock S, Fadaly W, Metwally MA. Eur. J. Med. Chem. 2009; 4813
  • 7 Nagarajan SR, De Crescenzo GA, Getman DP, Lu H.-F, Sikorski JA, Walker JL, McDonald JJ, Houseman KA, Kocan GP, Kishore N, Mehta PP, Funkes-Shippy CL, Blystone L. Bioorg. Med. Chem. 2003; 11: 4769
    CrossrefSearch in Google Scholar
  • 9 Bahrami K, Khodaei MM, Naali F. J. Org. Chem. 2008; 73: 6835
    CrossrefPubMedSearch in Google Scholar
  • 10 Sun Y, Duan L, Wei P, Qiao J, Dong G, Wang L, Qiu Y. Org. Lett. 2009; 11: 2069
    CrossrefSearch in Google Scholar
  • 13 Raghavendra GM, Ramesha AB, Revanna CN, Nandeesh KN, Mantelingu K, Rangappa KS. Tetrahedron Lett. 2011; 52: 5571
    CrossrefSearch in Google Scholar
    • 15a Kumar R, Selvam C, Kaur G, Chakraborti AK. Synlett 2005; 1401
      Thieme Connect
    • 15b Seijas JA, Vazquez-Tato MP, Carballido-Reboredo MR, Crecente Campo J, Romar-Lopez L. Synlett 2007; 313
    • 15c Ertan T, Yildiz I, Tekiner-Gulbas B, Bolelli K, Temiz-Arpaci O, Ozkan S, Kaynak F, Yalcin I, Aki E. Eur. J. Med. Chem. 2009; 501
    • 15d Terashima M, Ishii M, Kanaoka Y. Synthesis 1982; 484
      Thieme Connect
    • 15e Hein DW, Alheim RJ, Leavitt JJ. J. Am. Chem. Soc. 1957; 79: 427
      CrossrefSearch in Google Scholar
    • 15f So YH, Heeschen JP. J. Org. Chem. 1997; 62: 3552
      CrossrefSearch in Google Scholar
    • 15g Riadi Y, Mamouni R, Azzalou R, Haddad ME, Routier S, Guillaumet G, Lazar S. Tetrahedron Lett. 2011; 52: 3492
      CrossrefSearch in Google Scholar
    • 15h Tomoki Y, Hayato T, Tetsuya S, Masahiro M. Tetrahedron Lett. 2008; 49: 1598
      CrossrefSearch in Google Scholar
  • 16 Corma A, Garcia H. Chem. Rev. 2003; 103: 4307
    CrossrefPubMedSearch in Google Scholar
  • 17 Trivedi R, De SK, Gibbs RA. J. Mol. Catal. A: Chem. 2008; 245: 8
    Search in Google Scholar
  • 18 Li C.-J, Trost BM. Proc. Natl. Acad. Sci. U.S.A. 2008; 105: 13197
    CrossrefPubMedSearch in Google Scholar
  • 23 Gorepatil PB, Mane YD, Surywanshi VS, Shinde VS, Ingle VS. J. Curr. Chem. Pharm. Sci. 2012; 2: 367
    Search in Google Scholar
  • 24 General Procedure To a mixture of the requisite o-aminophenol/o-amino-thiophenol (1 mmol) and aldehyde (1 mmol) in EtOH–H2O (2:2 mL), samarium triflate catalyst (10 mol%) was added, and the resulting mixture was stirred at 60 °C. After completion of the reaction, as monitored by TLC, the mixture was diluted with H2O–EtOAc (1:1, 10 mL) and catalyst recovered by filtration. The filtrate was extracted with Et2O (2 × 10 mL) and dried with anhydrous Na2SO4. After filtration and evaporation of solvent, the crude product was recrystallized from EtOAc or MeOH. All the structures were confirmed by their analytical data and comparison with literature data.25–30 Spectroscopic Data for Selected Compounds 2-Phenylbenzo[d]oxazole (Table 2 Entry 1) Mp 100–102 °C. 1H NMR (300 MHz, DMSO-d 6): δ = 7.39 (m, 2 H), 7.57 (m, 3 H), 7.64 (m, 1 H), 7.80 (m, 1 H), 8.29 (m, 2 H). 13C NMR (75 MHz, DMSO-d 6): δ = 110.6, 119.9, 124.5, 125.1, 127.3, 127.5, 128.9, 131.5, 142.2, 150.8, 163.0. IR (KBr): 740, 1171, 1355, 1511, 1640, 3100 cm–1. MS (EI): m/z = 195.1 [M+]. 2-(4-Methylphenyl)benzo[d]oxazole (Table 2 Entry 3) Mp 114–116 °C. 1H NMR (300 MHz, DMSO-d 6): δ = 2.45 (s, 3 H), 7.36 (d, 2 H, J = 8.1 Hz), 7.41 (t, 1 H, J = 8.4 Hz), 7.51 (t, 1 H, J = 8.4 Hz), 7.96 (d, 1 H, J = 8.0 Hz), 8.00–8.06 (m, 3 H). 13C NMR (75 MHz, DMSO-d 6): δ = 21.2, 121.6, 122.9, 125.0, 126.2, 127.3, 129.7, 131.0, 135.0, 141.6, 154.2, 168.0. IR (KBr): 760, 1186, 1409, 1590, 1621, 2968 cm–1. MS (EI): m/z = 209.07 [M+]. 2-(4-Chlorophenyl)benzo[d]oxazole (Table 2 Entry 4) Mp 147–149 °C. 1H NMR (300 MHz, DMSO-d 6): δ = 7.44 (t, 1 H, J = 7.6 Hz), 7.50–7.56 (m, 3 H), 7.98 (d, 1 H, J = 8.1 Hz), 8.05–8.09 (m, 3 H). 13C NMR (75 MHz, DMSO-d 6): δ = 121.7, 123.2, 125.4, 126.5, 128.7, 129.2, 132.2, 135.1, 136.8, 154.1, 166.5. IR (KBr): 775, 1175, 1371, 1640, 2980 cm–1. MS (EI): m/z = 229 [M+] and 231 [M + 2]. 2-(4-Nitrophenyl)benzo[d]thiazole (Table 2 Entry 11) Mp 225–227 °C. 1H NMR (300 MHz, DMSO-d 6): δ = 7.51 (t, 1 H, J = 7.5 Hz), 7.60 (t, 1 H, J = 7.6 Hz), 8.01 (d, 1 H, J = 7.8 Hz), 8.16 (d, 1 H, J = 8.1 Hz), 8.36 (q, 4 H, J = 9.4 Hz). 13C NMR (75 MHz, DMSO-d 6): δ = 121.9, 123.8, 124.4, 126.1, 126.8, 128.2, 135.6, 139.2, 149.0, 154.1, 165.0. IR (KBr): 807, 1169, 1370, 1556, 1690, 3056 cm–1. MS (EI): m/z = 256.0 [M+]. 2-(Pyridin-4-yl)benzo[d]thiazole (Table 2 Entry 14) Mp 130–132 °C. 1H NMR (300 MHz, DMSO-d 6): δ = 7.44–7.50 (m, 2 H), 7.57 (t, 1 H, J = 8.1 Hz), 8.01 (d, 1 H, J = 7.9 Hz), 8.13 (d, 1 H, J = 8.2 Hz), 8.40 (dt, 1 H, J = 8.0, 1.7 Hz), 8.73 (dd, 1 H, J = 4.8z, 1.7 Hz). 13C NMR (75 MHz, DMSO-d 6): δ = 121.8, 123.3, 123.8, 125.6, 129.6, 134.4, 135.1, 148.5, 154.0, 164.7. IR (KBr): 690, 1150, 1400, 1653, 2360, 2905 cm–1. MS (EI): m/z = 212.03 [M+]. 2-(4-Methoxyphenyl)benzo[d]thiazole (Table 2 Entry 15) Mp 122–124 °C. 1H NMR (300 MHz, DMSO-d 6): δ = 3.89 (s, 3 H), 7.02 (d, 2 H, J = 8.4 Hz), 7.39 (t, 1 H, J = 7.2 Hz), 7.51 (t, 1 H, J = 7.2 Hz), 7.94 (d, 1 H, J = 7.8 Hz), 8.06 (m, 3 H). 13C NMR (75 MHz, DMSO-d 6): δ = 55.4, 114.3, 121.6, 122.7, 124.8, 126.2, 126.4, 129.0, 135.0, 154.3, 162.0, 167.7. IR (KBr): 781, 1170, 1450, 1597, 1650, 3010 cm–1. MS (EI): m/z = 241 [M+].
  • 25 Ranjit S, Liu X. Chem. Eur. J. 2011; 17: 1105
    CrossrefSearch in Google Scholar
  • 26 Huang J, Chan J, Chen Y, Borths CJ, Baucom KD, Larsen RD, Faul MM. J. Am. Chem. Soc. 2010; 132: 3674
    CrossrefSearch in Google Scholar
  • 27 Devalla VR, Ethirajulu K. J. Chem. Soc. 1995; 1497
  • 28 Bougrin K, Loupy A, Soufiaoui M. Tetrahedron 1998; 54: 8055
    CrossrefSearch in Google Scholar
  • 29 Balaji SL, Umesh RP, Jyotirling RM, Ramrao AM. Bull. Korean Chem. Soc. 2010; 31: 2329
    CrossrefSearch in Google Scholar
  • 30 Shi D.-F, Bradshaw TD, Wrigley S, McCall CJ, Lelieveld P, Fichtner I, Stevens MF. G. J. Med. Chem. 1996; 39: 3375
    CrossrefSearch in Google Scholar

   Permissions and Reprints All articles of this category
Zoom Image
Scheme 1 Samarium triflate [Sm(OTf)3] catalyzed synthesis of ­2-substituted benzoxazoles and benzothiazoles