Synthesis of O,O-Diethyl Arylthiophosphonate from O-Aryl-O,O-diethylthiophosphate

Abstract

The synthesis of O,O-diethyl 2-hydroxyarylthiophosphonate is reported by using a [1,3]-rearrangement. This method is achieved in high yield from ortho-bromophenols derivatives by a two-step process

Key words

phosphorylation - metallation - phenols - rearrangement

References and Notes

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13

Preparation of Thiophosphates 1a-i Represented by the Preparation of O , O- Diethyl 6-Bromo-2-(diethoxythio-phosphinyl)-4-methylphenylthiophosphonate (1g): A solution of the phenolic derivative 2c (3.70 g, 8.85 mmol), triethylamine (1.48 mL, 10.6 mmol, 1.2 equiv) and DMAP (0.108 g, 0.88 mmol, 0.1 equiv) in THF (36 mL) was slowly added (15 min) to a solution of O,O-diethylchlorothio-phosphate (1.67 g, 8.85 mmol) in THF (10 mL). The solution was then stirred overnight. The obtained suspension was filtered on celite and washed with Et₂O. The filtrate was concentrated and redissolved in Et₂O (80 mL). The organic phase was washed with H₂O (2 × 20 mL) and brine (15 mL), dried over MgSO₄, filtered and concentrated. The obtained crude product was purified by column chromatography over silica gel (70-230 mesh; pentane-EtOAc, 100:5) to produce 1g (87% yield) as a colorless solid; mp 81 ˚C. ^¹H NMR (300 MHz, CDCl₃): δ = 1.33, 1.40 (2 × t, ^³ J _HH = 7.0 Hz, 12 H, CH ₃CH₂O), 2.34 (s, 3 H, Me), 4.14, 4.31 (2 × m, 8 H, CH₃CH ₂O), 7.57 (d, ⁵ J _HP = 1.8 Hz, 1 H, H5), 7.92 (d, ^³ J _HP = 19.0 Hz, 1 H, H3). ^³¹P (81.03 MHz, CDCl₃): δ = 62.2 (d, ⁴ J _PP = 2.7 Hz), 83.5 (d, ⁴ J _PP = 2.7 Hz). ^¹³C (75.48 MHz, CDCl₃): δ = 16.0 (m, CH₂ CH₃), 20.7 (s, Me), 63.3 (d, ^³ J _HP = 5 Hz, OCH₂CH₃), 65.2 (m, OCH₂CH₃), 117.6 (dd, ^³ J _CP = 12 Hz, ^³ J _CP = 5 Hz, CBr), 127.6 (dd, ^¹ J _CP = 143 Hz, ^³ J _CP = 5 Hz, C_ArP), 136.0-136.42 (m, 2 × C_Ar), 139.0 (s, C_ArH), 147.3 (m, C_ArO). IR (neat): 709, 735, 790, 889, 927, 966, 1018, 1245, 1432, 2979 cm^-¹. Anal. Calcd for C₁₅H₂₅BrO₅P₂S₂: C, 36.67; H, 5.13; S, 13.05. Found: C, 36.74; H, 5.10; S, 13.02.

14

Synthesis of Thiophosphonate 2-2i from Thiophosphate Represented by the Preparation of O , O -Diethyl 6-Hydroxy-2-pyridinylthiophosphonate (2f):
n-Butyllithium (1.5 M in n-hexane, 2.25 mL, 3.38 mmol, 1.1 equiv) was added dropwise to a solution of 1f (1 g, 3.07 mmol) in THF (10 mL) previously cooled to -78 ˚C. At the end of the addition, the solution was left to warm slowly. Then an aqueous solution of ammonium chloride was added (10 mL). The aqueous phase was extracted with Et₂O (3 × 30 mL). The combined organic phases were washed with H₂O and dried over MgSO₄. After filtration and concentration the crude product was purified by column chromatography over silica gel (PE-EtOAc, 5:1) to produce the pure compound 2f as a white solid in 85% yield; mp 70 ˚C. ^¹H NMR (300 MHz, CDCl₃): δ = 1.37 (t, ^³ J _HH = 7.0 Hz, 6 H, OCH₂CH ₃), 4.26 (m, 4 H, OCH ₂CH₃), 7.31 (dd, ^³ J _HH = 7.0 Hz, ^³ J _HP = 1.0 Hz, 1 H, C4-H), 7.36 (m, 1 H, C5-H), 8.34 (dt, ^³ J _HH = 5.0 Hz, ⁴ J _HP = 1.0 Hz, 1 H, C6-H), 9.65 (s, 1 H, OH). ^³¹P NMR (81.03 MHz, CDCl₃): δ = 69.7. ^¹³C NMR (75.48 MHz, CDCl₃): δ = 16.0 (d, ^³ J _CP = 7 Hz, OCH₂ CH₃), 63.6 (d, ^² J _CP = 6 Hz, OCH₂CH₃), 126.4 (d, ^³ J _CP = 10 Hz, C4), 128.4 (d, ⁴ J _CP = 4 Hz, C5), 135.4 (d, ^¹ J _CP = 188 Hz, C2), 141.9 (d, ^³ J _CP = 20 Hz, C6), 158.3 (d, ^² J _CP = 27 Hz, C3). Anal. Calcd for C₉H₁₄NO₃PS: C, 43.72; H, 5.71; N, 5.66; S, 12.87. Found: C, 44.19; H, 5.90; N, 5.30; S, 12.66. HRMS (ES-TOF): m/z
[M + H] calcd for C₉H₁₅NO₃PS: 248.0505; found: 248.0510. IR (neat): 953, 1009, 1306, 1455, 1570, 2733, 2927 cm^-¹.