Radion Reactions To Form Vinylphosphonothioates

Abstract

Radical addition of diethyl thiophosphite to terminal ­alkenes followed by consecutive α-silylation and Peterson reactions, efficiently forms vinylphosphonothioates, in one-pot radion reactions.

Key words

radical reaction - Peterson reaction - phosphorus hydride

References

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9

All new compounds gave consistent spectral and HRMS data.

10

Typical Procedure for the Preparation of O , O -Diethyl ( E , Z )-1-Heptyl-2-(4-methoxyphenyl)ethenylphosphono-thioate ( 6a).
A solution of 1-octene (0.14 mL, 0.89 mmol), diethyl thiophosphite (0.15 g, 0.98 mmol) and AIBN (0.036 g, 0.22 mmol) in anhyd THF (10 mL) was heated at reflux for 8 h. A further portion of AIBN (0.036 g, 0.22 mmol) was added and the reaction was heated again at reflux for further 16 h then cooled to -78 °C. s-BuLi (1.59 mL of a 1.4 M solution in cyclohexane, 2.23 mmol) was added and the reaction was stirred at -78 °C for 0.5 h. After this time a solution of freshly distilled chlorotrimethylsilane (0.23 mL, 1.78 mmol) in anhyd THF (1.0 mL) was added and the reaction was warmed to r.t. and stirred at this temperature for 0.5 h. The reaction mixture was again cooled to -78 °C and s-BuLi (0.76 mL of a 1.4 M solution in cyclohexane, 1.07 mmol) was added and the reaction was stirred at this temperature for 0.25 h after which time a solution of 4-methoxybenz-aldehyde (0.17 mL, 1.42 mmol) in anhyd THF (1.0 mL) was added. The reaction mixture was allowed to warm slowly to r.t. and was stirred at this temperature for 16 h. The reaction was then quenched with NH₄Cl (10 mL of a sat. aq solution) and extracted with Et₂O (3 × 25 mL). The combined organic phases were dried over MgSO₄, filtered and concentrated to afford a crude residue that was purified by flash column chromatography on silica using PE-Et₂O with a solvent gradient of (199:1 to 9:1) as eluent to afford vinylphos-phonothioate 6a (0.28 g, 83%) as a colourless oil and as an inseparable 1:10 mixture of E- and Z-isomers as judged from the ¹H NMR spectrum.
Compound (Z)-6a: R _f = 0.20 (PE-Et₂O, 9:1). IR (neat):
ν_max = 2956 (s), 2925 (s), 2855 (s), 1607 (s), 1509 (s), 1464 (m), 1442 (w), 1388 (w), 1296 (w), 1253 (s), 1178 (s), 1049 (s), 1029 (s) cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 7.52 (d, J = 8.5 Hz, 2 H, C=CH, Ar), 6.95 (d, ³ J _HP = 49.5 Hz, 1 H, PC=CH), 6.84 (d, J = 8.5 Hz, 2 H, CH=COMe, Ar), 3.90 (dq, ³ J _HP = 9.5 Hz, J = 7.0 Hz, 4 H, 2 × POCH ₂), 3.66 (s, 3 H, OCH ₃), 2.44 (dt, ² J _HP = 15.0 Hz, J = 7.5 Hz, 2 H, PCCH ₂), 1.72-1.58 (m, 2 H, PCCH₂CH ₂), 1.41-1.25 (m, 8 H, 4 × CH ₂) 1.07 (t, J = 7.0 Hz, 6 H, 2 × OCH₂CH ₃), 0.89 (t, J = 6.5 Hz, 3 H, CH ₃). ¹³C NMR (100 MHz, CDCl₃): δ = 159.5 (COMe, Ar), 140.4 (d, ² J _CP = 8.5 Hz, PC=CH), 133.4 (d, ¹ J _CP = 137.5 Hz, PC=CH), 130.9 (d, ⁴ J _CP = 2.5 Hz, C=CH, Ar), 128.9 (d, ³ J _CP = 7.0 Hz, PC=CHC, Ar), 112.8 (CH=COMe), 61.9 (d, ² J _CP = 7.0 Hz, 2 × OCH₂), 55.06 (OCH₃), 36.3 (d, ² J _CP = 14.0 Hz, PCCH₂), 31.7 (CH₂), 30.0 (d, ³ J _CP = 3.0 Hz, PCCH₂ CH₂), 29.1 (CH₂), 28.9 (CH₂), 22.5 (CH₂CH₃), 15.6 (d, ³ J _CP = 8.5 Hz, 2 × OCH₂ CH₃), 13.9 (CH₃). MS (CI, NH₃): m/z (%) = 385 (100) [M + H⁺]. HRMS: m/z calcd for C₂₀H₃₃O₃PS: 385.1966 [M + H⁺]. Found: 385.1964 [M + H⁺]. The presence of compound (E)-6a was given by the following signals in the ¹H NMR and ¹³C NMR spectra. ¹H NMR (400 MHz, CDCl₃): δ = 7.35 (d, J = 8.5 Hz, 2 H, C=CH, Ar), 4.16-4.08 (m, 4 H, 2 ¥ POCH ₂), 3.83 (dq, ³ J _HP = 8.5 Hz, J = 7.0 Hz, 2 H, POCH ₂), 2.60-2.51 (m, 2 H, PCCH ₂), 1.33 (t, J = 7.0 Hz, 6 H, 2 × OCH₂CH ₃). ¹³C NMR (100 MHz, CDCl₃): δ = 159.5 (COMe, Ar), 141.8 (d, ² J _CP = 17.5 Hz, C=CH), 113.7 (CH=COMe), 62.2 (d, ² J _CP = 6.0 Hz, 2 × OCH₂), 55.08 (OCH₃), 16.0 (d, ³ J _CP = 7.5 Hz, 2 × OCH₂ CH₃).