Radical Addition Reactions of Diphenylphosphine Sulfide

Abstract

Radical additions of diphenylphosphine sulfide [Ph₂P(S)H] to various C=C bonds offers a general, mild and ­efficient approach to alkyl(diphenyl)phosphine sulfides.

Key words

radical reaction - phosphorus hydride - C=C bonds

References

• Selected examples:
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3

Pantazis, D.; McGrady, J. E. unpublished results.

6

Performed in a CEM Focused Microwave Synthesis System.

7

All new compounds gave consistent spectral and HRMS data.

8

Typical Procedure. To diphenylphosphine sulfide (0.327 g, 3 equiv, 1.5 mmol) in a N₂ flushed flask was added non-degassed dioxane (2 mL), followed by methyl methacrylate (0.053 mL, 0.5 mmol). Then, Et₃B (1 M solution in hexane, 0.15 mL, 0.3 equiv, 0.15 mmol) was added and the reaction was left to stir for 4 h. After this time a further portion of Et₃B (1 M solution in hexane, 0.15 mL, 0.3 equiv, 0.15 mmol) was added, and the mixture was left to stir for 16 h. The reaction mixture was then concentrated in vacuo to afford the crude product. Following column chromatography (4:1, PE-EtOAc), methyl 3-(diphenylphosphorothioyl)-2-methylpropanoate (9) was isolated as a colourless oil (0.147 g, 92%); R _f = 0.2 (4:1, PE-EtOAc). IR (thin film): ν_max = 3054 (m), 2975 (m), 2949 (m), 1731 (s, C=O), 1436 (s, P-Ph), 1309 (m), 1274 (m), 1211 (s), 1158 (s), 1102 (s), 1027 (m), 998 (m) cm^-1.
¹H NMR (400 MHz, CDCl₃): δ = 7.91-7.80 (4 H, m, 4 × CH Ar), 7.54-7.41 (6 H, m, 6 × CH Ar), 3.46 (3 H, s, O-CH ₃), 3.21-3.08 [2 H, m, P(S)CH ₂-CH], 2.52-2.41 [1 H, m, P(S)CH₂-CH], 1.18 (3 H, d, J = 7 Hz, CH₂-CH-CH ₃).
¹³C NMR (100.6 MHz, CDCl₃): δ = 175.8 (d, ³ J _C-P = 9.5 Hz, O=C-O-CH₃), 133.1 (d, ¹ J _C-P = 80.5 Hz, C _q Ar), 132.3 (d, ¹ J _C-P = 80.5 Hz, C _q Ar), 131.6 (d, ⁴ J _C-P = 3.0 Hz, CH Ar), 131.5 (d, ⁴ J _C-P = 3.0 Hz, CH, Ar), 131.3 (d, ² J _C-P = 10.5 Hz, 2 × CH Ar), 131.0 (d, ² J _C-P 10.0 Hz, 2 × CH Ar), 128.7 (d, ³ J _C-P 12.0 Hz, 2 × CH Ar), 128.5 (d, ³ J _C-P = 12.0 Hz, 2 × CH Ar), 51.9 (O-CH₃), 35.5 [d, ¹ J _C-P = 57 Hz, P(S)CH₂], 34.3 [d, ² J _C-P = 1 Hz, P(S)CH₂-CH], 19.4 (d, ³ J _C-P = 8.5 Hz, CH₂-CH-CH₃). ³¹P NMR (161.9 MHz, CDCl₃): δ = 41.3 [Ph₂ P(S)]. MS (CI, NH₃): m/z (%) = 319 (100), 218 (17). HRMS: m/z calcd for C₁₇H₁₉O₂PS: [M + H⁺] 319.0922 (0.2 ppm); found: [M + H⁺] 319.0921.

9

Deprotonation of Ph₂P(S)H and addition to electron-poor alkenes has been reported previously (see ref. 4).