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

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.

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

References

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<A NAME="RD20204ST-22">22</A>

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.

<A NAME="RD20204ST-23">23</A>

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.