Synlett 2013; 24(12): 1558-1562
DOI: 10.1055/s-0033-1339194
letter
© Georg Thieme Verlag Stuttgart · New York

Catalyst- and Metal-Free Rapid Functionalizations of Alkynes Using TsNBr2

Ruchi Chawla
Green Synthesis Lab, Department of Chemistry, University of Allahabad, Allahabad 211 002, India   Fax: +91(532)2460533   Email: ldsyadav@hotmail.com
,
Atul K. Singh
Green Synthesis Lab, Department of Chemistry, University of Allahabad, Allahabad 211 002, India   Fax: +91(532)2460533   Email: ldsyadav@hotmail.com
,
Lal Dhar S. Yadav*
Green Synthesis Lab, Department of Chemistry, University of Allahabad, Allahabad 211 002, India   Fax: +91(532)2460533   Email: ldsyadav@hotmail.com
› Author Affiliations
Further Information

Publication History

Received: 02 May 2013

Accepted after revision: 20 May 2013

Publication Date:
20 June 2013 (online)


Abstract

A very rapid (3–12 min) and efficient method has been developed for a one-pot synthesis of α,α-dibromoalkanones and β-bromoenol alkanoates directly from alkynes using N,N-dibromo-p-toluenesulfonamide (TsNBr2). The protocol is embellished with features like ambient temperature, high regioselectivity, operational simplicity, and metal- and catalyst-free conditions.

 
  • References and Notes

  • 3 Palisse A, Kirsch SF. Org. Biomol. Chem. 2012; 10: 8041
  • 8 Kajigaeshi S, Kakinami T, Okamoto T, Fujisaki S. Bull. Chem. Soc. Jpn. 1987; 60: 1159
  • 9 Paul S, Gupta V, Gupta R, Loupy A. Tetrahedron Lett. 2003; 44: 439
  • 10 Ye C, Shreeve JM. J. Org. Chem. 2004; 69: 8561
  • 11 Pandit P, Gayen KS, Khamarui S, Chatterjee N, Maiti DK. Chem. Commun. 2011; 47: 6933
  • 12 Schmidt R, Stolle A, Ondruschka B. Green Chem. 2012; 14: 1673
  • 14 Kharasch MS, Priestley HN. J. Am. Chem. Soc. 1939; 61: 3425
  • 17 Shen R, Huang X. Org. Lett. 2009; 11: 5698
  • 19 Schmid GH, Modro A, Yates K. J. Org. Chem. 1980; 45: 665
  • 20 General Procedure for the Synthesis of α,α-Dibromoalkanones 3 A mixture of alkyne 1 (1.0 mmol) and TsNBr2 (2, 2.0 mmol) in MeCN (2 mL) with H2O (0.2 mL) was stirred at r.t. for 3–10 min (Table 2). After completion of the reaction (monitored by TLC), H2O was added and the mixture was extracted with EtOAc (3 × 5 mL). The combined organic phases were dried over anhyd Na2SO4, filtered, and concentrated under reduced pressure. The resulting crude product was purified by silica gel column chromatography using a mixture of EtOAc–n-hexane (1:99) as eluent to afford an analytically pure sample of α,α-dibromoalkanones 3 (Table 2). Characterization Data of Representative Compounds Compound 3a: viscous liquid; yield 87%. IR (neat): νmax = 3448, 2926, 1600, 1475, 1092 cm–1. 1H NMR (400 MHz, CDCl3): δ = 6.71 (s, 1 H), 7.49–7.57 (m, 2 H), 7.63–7.67 (m, 1 H), 8.08–8.10 (m, 2 H). 13C NMR (100 MHz, CDCl3): δ = 39.7, 128.9, 129.8, 130.3, 134.7, 185.7. MS (EI): m/z = 276 [M+], 278 [M+ + 2]. Anal. Calcd for C8H6Br2O: C, 34.57; H, 2.18. Found: C, 34.33; H, 2.26. Compound 3h: viscous liquid; yield 78%. IR (neat): νmax = 2960, 2938, 2871, 1720, 1461, 1380, 1243, 1147, 1105, 627 cm–1. 1H NMR (400 MHz, CDCl3): δ = 0.99 (m, 6 H), 1.70 (m, 4 H), 2.43 (m, 2 H), 3.09 (t, J = 7.2 Hz, 2 H). 13C NMR (100 MHz, CDCl3): δ = 13.1, 13.6, 18.6, 20.7, 38.3, 46.8, 71.5, 198.0. MS (EI): m/z = 284 [M+], 286 [M+ + 2]. Anal. Calcd for C8H14Br2O: C, 33.60; H, 4.93. Found: C, 33.52; H, 5.02.
  • 21 General Procedure for the Synthesis of Bromoenol Alkanoates 5 and 6 A mixture of alkyne 1 (2.0 mmol) and TsNBr2 (2, 1.0 mmol) in carboxylic acid 4 (2 mL) was stirred at r.t. for 3–12 min (Table 3). After completion of the reaction (monitored by TLC), H2O was added, and the mixture was extracted with EtOAc (3 × 5 mL). The combined organic phases were dried over anhyd Na2SO4, filtered, and concentrated under reduced pressure. The resulting crude product was purified by preparative chromatography using a mixture of EtOAc–n-hexane (1:99) as eluent to afford an analytically pure sample of bromoenol alkanoates 5 and 6 (Table 3). Characterization Data of Representative Compounds Compound 5a: yellow oil; yield 60%. IR (KBr): νmax = 3095, 2928, 2852, 1765, 1625, 1436, 1370, 1180, 1036, 740, 694, 627, 569, 488 cm–1. 1H NMR (400 MHz, CDCl3): δ = 2.34 (s, 3 H), 6.55 (s, 1 H), 7.33–7.35 (m, 3 H), 7.37–7.41 (m, 2 H). 13C NMR (100 MHz, CDCl3): δ = 20.5, 96.6, 124.3, 126.1, 128.5, 133.0, 150.2, 166.6. MS (EI): m/z = 240 [M+], 242 [M+ + 2]. Anal. Calcd for C10H9BrO2: C, 49.82; H, 3.76. Found: C, 49.46; H, 3.82. Compound 6a: yellow oil; yield 24%. IR (KBr): νmax = 3096, 2929, 2855, 1762, 1624, 1438, 1370, 1185, 1036, 740, 690, 625, 567, 489 cm–1. 1H NMR (400 MHz, CDCl3): δ = 2.17 (s, 3 H), 6.31 (s, 1 H), 7.34–7.43 (m, 4 H), 7.61–7.64 (m, 1 H). 13C NMR (100 MHz, CDCl3): δ = 20.3, 94.6, 124.8, 128.5, 129.3, 133.2, 148.7, 167.3. MS (EI): m/z = 240 [M+], 242 [M+ + 2]. Anal. Calcd for C10H9BrO2: C, 49.82; H, 3.76. Found: C, 49.55; H, 3.78. Compound 5d: yellow oil; yield 54%. IR (KBr): νmax = 3094, 2938, 1765, 1609, 1510, 1458, 1370, 1035, 896, 835, 770, 658, 597, 512 cm–1. 1H NMR (400 MHz, CDCl3): δ = 2.31 (s, 3 H), 3.76 (s, 3 H), 6.37 (s, 1 H), 6.85 (d, J = 8.8 Hz, 2 H), 7.33 (d, J = 8.8 Hz, 2 H). 13C NMR (100 MHz, CDCl3): δ = 20.8, 55.2, 96.4, 113.5, 125.3, 126.3, 150.2, 160.1, 167.3. MS (EI): m/z = 270 [M+], 272 [M+ + 2]. Anal. Calcd for C11H11BrO3: C, 48.73; H, 4.09. Found: C, 48.44; H, 4.12. Compound 6d: yellow oil; yield 20%. IR (KBr): νmax = 3092, 2940, 1763, 1606, 1514, 1457, 1370, 1035, 898, 835, 770, 657, 595, 511 cm–1. 1H NMR (400 MHz, CDCl3): δ = 2.13 (s, 3 H), 3.80 (s, 3 H), 6.22 (s, 1 H), 6.87 (d, J = 9.2 Hz, 2 H), 7.56 (d, J = 8.0 Hz, 2 H).13C NMR (100 MHz, CDCl3): δ = 20.5, 55.3, 94.4, 114.1, 125.8, 129.7, 148.5, 160.4, 168.6. MS (EI): m/z = 270 [M+], 272 [M+ + 2]. Anal. Calcd for C11H11BrO3: C, 48.73; H, 4.09. Found: C, 48.40; H, 4.19.