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Synlett 2005(2): 299-303  
DOI: 10.1055/s-2004-837212
LETTER
© Georg Thieme Verlag Stuttgart · New York

H3PW12O40 as a Useful Recyclable Heterogeneous Catalyst for the Facile and Highly Efficient Michael Addition Reaction of Thiols to α,β-Unsaturated Ketones

Habib Firouzabadi*, Nasser Iranpoor*, Abbas Ali Jafari
Chemistry Department, College of Sciences, Shiraz University, Shiraz 71454, Iran
e-Mail: firouzabadi@chem.susc.ac.ir; e-Mail: iranpoor@chem.susc.ac.ir ;
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Publikationsverlauf

Received 20 July 2004
Publikationsdatum:
17. Dezember 2004 (online)

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Abstract

Solid H3PW12O40 is easily used as a heterogeneous, re­usable and efficient catalyst (1 mol%) for the selective addition of thiols and dithiols to α,β-unsaturated ketones in MeCN to afford the corresponding Michael adducts in excellent yields at room ­temperature.

Key words

dodecatangstophosphoric acid - H3PW12O40 - Michael addition - α,β-unsaturated ketones

22

General Procedure for the 1,4-Conjugate Addition of Thiols to α,β-Unsaturated Ketones:
To a mixture of the α,β-unsaturated ketone (5 mmol) and the thiol (5 mmol) in MeCN (10 mL), H3PW12O40 (1 mol%, 0.144 g) was added and the resulting heterogenous mixture was stirred at r.t. for the appropriate reaction time (Table [1] ). After completion of reaction (monitored by TLC), the catalyst was filtered off and the filtrate was evaporated under vacuum to afford the desired product in high purity in excellent yield. Structural assignments of the products are based on their 1H NMR, 13C NMR, IR, MS spectra and elemental analysis and also compared with some of those reported.
Spectroscopic data of the unknown Michael adducts:
Table 1, Entry 4: 1H NMR (250 MHz, CDCl3): δ = 3.15 (m, 1 H), 2.71-2.64 (m, 2 H), 2.41-2.31 (m, 3 H), 2.15-2.11 (m, 2 H), 1.92 (m, 2 H), 1.74-1.63 (m, 5 H), 1.35-1.28 (m, 5 H) ppm. 13C NMR (63 MHz, CDCl3): δ = 209.11, 49.00, 42.36, 41.38, 34.51, 33.11, 26.28, 25.61 ppm. IR: ν = 2920, 2880, 1710, 1425, 1200 cm-1. MS: m/e = 212 [M]+. Anal. Calcd for C12H20OS: C, 67.88; H, 9.49. Found: C, 67.25; H, 9.48.
Table 1, Entry 8: 1H NMR (250 MHz, CDCl3): δ = 3.53 (m, 1 H), 2.71-2.61 (m, 1 H), 2.58-2.55 (m, 1 H), 2.38 (m, 2 H), 2.22 (m, 2 H), 2.19-2.15 (m, 2 H), 1.94 (m, 3 H), 1.76-1.63 (m, 2 H), 1.33-1.30 (m, 6 H) ppm. 13C NMR (63 MHz, CDCl3): δ = 215.47, 45.04, 42.27, 37.40, 35.93, 32.59, 29.16, 24.69 ppm. IR: ν = 2920, 2880, 1725, 1425, 1180 cm-1. MS: m/e = 198 [M]+. Anal. Calcd for C11H18OS: C, 66.62; H, 9.15. Found: C, 66.58; H, 9.14.
Table 1, Entry 12: 1H NMR (250 MHz, CDCl3): δ = 2.75-2.73 (dd + m, 5 H), 2.17-2.18 (m, 2 H), 2.00 (m, 2 H), 1.77 (m, 2 H), 1.63 (m, 1 H), 1.30 (m, 6 H) ppm. 13C NMR (63 MHz, CDCl3): δ = 207.25, 44.08, 34.34, 30.74, 26.10, 24.10 ppm. IR: ν = 2920, 2880, 1710, 1425, 1350 cm-1. MS: m/e = 186 [M]+. Anal. Calcd for C10H18OS: C, 64.47; H, 9.74. Found: C, 64.48; H, 9.74. Table 1, Entry 13: 1H NMR (250 MHz, CDCl3): δ = 7.50-7.70 (m, 3 H), 7.15-7.30 (m, 7 H), 4.60 (t, 1 H), 2.80-3.10 (dd, 2 H), 2.15 (s, 3 H) ppm. 13C NMR (63 MHz, CDCl3): δ = 205.88, 141.51, 137.43, 133.28, 129.44, 129.22, 129.05, 128.18, 128.06, 49.89, 48.45, 30.71 ppm. IR: ν = 3070, 2920, 1710, 1560, 1490, 1350 cm-1. MS: m/e = 256 [M]+. Anal. Calcd for C16H16OS: C, 74.96; H, 6.29. Found: C, 75.2; H, 6.28. Table 1, Entry 15: 1H NMR (250 MHz, CDCl3): δ = 7.35-7.16 (m, 10 H), 4.60 (t, 1 H), 3.50 (s, 2 H), 2.80-2.60 (dd, 2 H), 2.15 (s, 3 H) ppm. 13C NMR (63 MHz, CDCl3): δ = 205.88, 141.51, 134.10, 129.44, 129.22, 129.05, 128.18, 128.06, 49.20, 48.45, 38.81, 30.71 ppm. IR: ν = 3070, 2920, 1710, 1560, 1490, 1350 cm-1. MS: m/e = 270 [M]+. Anal. Calcd for C17H18OS: C, 75.52; H, 6.71. Found: C, 75.31; H, 6.68.

23

General Procedure for the Double Conjugate Addition of Thiols to α,β-Unsaturated Ketones:
To the mixture of the α,β-unsaturated ketone (4.5 mmol) and H3PW12O40 (1 mol%, 0.06 g) in MeCN (5 mL), a solution of dithiol (2 mmol) in MeCN (5 mL) was added dropwise at r.t. for the appropriate reaction time (Table [2] ). The catalyst was filtered off after the completion of reaction (monitored by TLC). The filtrate was evaporated under vacuum and the resulting crude product was purified by column chromatography eluting with petroleum ether-EtOAc (2:1). Structural assignments of the products are based on their 1H NMR, 13C NMR, IR, MS spectra and elemental analysis.
Spectroscopic data of the novel Michael adducts: Table 2, Entry 1: 1H NMR (250 MHz, CDCl3): δ = 2.76-2.70 (m, 12 H), 2.18 (s, 6 H) ppm. 13C NMR (63 MHz, CDCl3): δ =207.00, 43.97, 32.63, 30.45, 26.01 ppm. IR: ν = 2860, 1710, 1410, 1350, 1170 cm-1. MS: m/e = 234 [M]+. Anal. Calcd for C10H18O2S2: C, 51.25; H, 7.74. Found: C, 51.19; H, 7.72. Table 2, Entry 2: 1H NMR (250 MHz, CDCl3): δ = 2.74 (m, 8 H), 2.62 (m, 4 H), 2.18 (s, 6 H), 2.18 (t, 2 H) ppm. 13C NMR (63 MHz, CDCl3): δ = 207.13, 43.91, 31.33, 30.43, 29.34, 26.00 ppm. IR: ν = 2860, 1710, 1410, 1350, 1170
cm-1. MS: m/e = 248 [M]+. Anal. Calcd for C11H20O2S2: C, 53.19; H, 8.12. Found: C, 53.15; H, 8.11. Table 2, Entry 3: 1H NMR (250 MHz, CDCl3): δ = 3.20-3.10 (m, 2 H), 2.76 (m, 4 H), 2.70-2.65 (m, 2 H), 2.42-2.32 (m, 6 H), 2.16-2.13 (m, 4 H), 1.74-1.70 (m, 4 H) ppm. 13C NMR (63 MHz, CDCl3): δ = 208.53, 48.27, 42.68, 41.09, 31.74, 30.91, 24.25 ppm. IR: ν = 2930, 1710, 1410, 1350, 1170 cm-1. MS: m/e = 286 [M]+. Anal. Calcd for C14H22O2S2: C, 58.70; H, 7.74. Found: C, 58.64; H, 7.73. Table 2, Entry 4: 1H NMR (250 MHz, CDCl3): δ = 3.01-3.00 (m, 2 H), 2.74-2.62 (t + m, 6 H), 2.42-2.33 (m, 6 H), 2.17-2.12 (m, 4 H), 1.87-1.69 (m, 6 H) ppm. 13C NMR (63 MHz, CDCl3): δ = 209.10, 48.47, 43.24, 41.28, 31.93, 29.74, 29.73, 24.51 ppm. IR: ν = 2930, 1710, 1410, 1350, 1170 cm-1. MS: m/e = 300 [M]+. Anal. Calcd for C15H24O2S2: C, 59.96; H, 8.05. Found: C, 59.92; H, 8.02. Table 2, Entry 5: 1H NMR (250 MHz, CDCl3): δ = 3.50-3.55 (m, 2 H), 2.82 (s, 4 H), 2.68-2.58 (m, 2 H), 2.44-2.35 (m, 4 H), 2.27-2.16 (m, 4 H), 2.04-1.96 (m, 2 H) ppm. 13C NMR (63 MHz, CDCl3): δ = 216.52, 46.06, 41.03, 37.40, 31.84, 30.34. IR: ν = 2930, 1725, 1410, 1350, 1170 cm-1. MS: m/e = 258 [M]+. Anal. Calcd for C12H18O2S2: C, 55.78; H, 7.02. Found: C, 55.78; H, 7.01. Table 2, Entry 6: 1H NMR (250 MHz, CDCl3): δ = 3.50-3.45 (m, 2 H), 2.72-2.57 (t + m, 6 H), 2.43-2.34 (m, 4 H), 2.27-2.19 (m, 4 H), 1.97-1.89 (m, 4 H) ppm. 13C NMR (63 MHz, CDCl3): δ = 216.87, 46.10, 40.90, 37.45, 30.50, 29.62 ppm. IR: ν = 2930, 1725, 1410, 1350, 1170 cm-1. MS: m/e = 272 [M]+. Anal. Calcd for C13H20O2S2: C, 57.32; H, 7.40. Found: C, 57.28; H, 7.40.