An Expedient Reduction of sec-Phosphine Oxides to sec-Phosphine-boranes by BH3˙SMe2

Marek Stankevič; K. Michał Pietrusiewicz

doi:10.1055/s-2003-39304

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Synlett 2003(7): 1012-1016
DOI: 10.1055/s-2003-39304

LETTER

An Expedient Reduction of sec-Phosphine Oxides to sec-Phosphine-boranes by BH₃˙SMe₂

Marek Stankevič^a, K. Michał Pietrusiewicz*^a,b
Institute of Organic Chemistry, Polish Academy of Science, ul. Kasprzaka 44/52, 01-224 Warsaw, Poland
Department of Organic Chemistry, Maria Curie-Skodowska University, ul. Gliniana 33, 20-614 Lublin, Poland
Fax: +48(22)63266 81; e-Mail: kmp@icho.edu.pl;

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Publication History

Received 22 March 2003
Publication Date:
20 May 2003 (online)

Abstract
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Abstract

Secondary phosphine oxides can be expeditiously converted into secondary phosphine-boranes by treatment with an excess of BH₃˙SMe₂ at room temperature. Selectivity of the conversion towards the formation of secondary phosphine-boranes is greatly improved by the addition of a small amount of water to the reaction mixture.

Key word

phosphorus - boron - complexes - reductions - stereoselectivity

References

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14

Typical procedure for the reduction of secondary phosphine oxides with BH₃˙THF complex:
To a solution of secondary phosphine oxide (0.5 mmol) in 10 mL of dry THF was added through a syringe 1.5 mmol of BH₃˙THF complex. The mixture was stirred at room temperature for 15 min-2 h (see Table [1] ). Then reaction mixture was evaporated to dryness and the crude product was purified by column chromatography (hexane:ethyl acetate, 6:1, then hexane:ethyl acetate, 2:1).
Phosphine-boranes 2a, 2b, 2j were known compounds. [8a] Data for new compounds follow:
Benzylphenylphosphine-borane (2c). Yield 84%; ¹H NMR (CDCl₃) δ = 0.12-1.90 (br m, 3 H), 3.11-3.50 (m, 2 H), 5.53 (dq, J _P-H = 376 Hz, 1 H), 6.96-7.10 (m, 2 H), 7.22-7.31 (m, 3 H), 7.37-7.60 (m, 5 H) ppm; ¹³C NMR (CDCl₃) δ = 31.94, 32.56, 125.02, 125.55, 127.03, 127.08, 128.54, 128.60, 128.81, 129.09, 129.18, 131.71, 131.76, 132.97, 133.14, 133.25 ppm; ³¹P NMR (CDCl₃) δ = 8.10 ppm (m); Anal for C₁₃H₁₆BP Calcd: C 72.95, H 7.53 Found: C 72.95, H 7.60.
(1-Naphthylmethyl)phenylphosphine-borane (2d). Yield 87%; ¹H NMR (CDCl₃) δ = 0.20-1.90 (br m, 3 H), 3.47-4.02 (m, 2 H), 5.58 (dq, J _P-H = 374 Hz, 1 H), 7.02-7.11 (m, 1 H), 7.28-7.69 (m, 8 H), 7.77-7.98 (m, 3 H) ppm; ¹³C NMR (CDCl₃) δ = 29.49, 30.10, 123.01, 124.33, 125.11, 125.17, 125.87, 126.41, 127.77, 127.87, 127.96, 128.02, 128.50, 128.70, 129.00, 129.52, 129.72, 130.92, 131.68, 131.74, 132.96, 133.12, 133.85 ppm; ³¹P NMR (CDCl₃) δ = 5.48 ppm (m); Anal for C₁₇H₁₈BP Calcd: C 77.31, H 6.87 Found: C 77.21, H 6.99.
(2-Naphthylmethyl)phenylphosphine-borane (2e). Yield 71%; ¹H NMR (CDCl₃) δ = 0.15-1.85 (br m, 3 H), 3.30-3.68 (m, 2 H), 5.60 (dq, J _P-H = 374 Hz, 1 H), 7.12-7.17 (m, 1 H), 7.34-7.60 (m, 8 H), 7.68-7.89 (m, 3 H) ppm; ¹³C NMR (CDCl₃) δ = 32.19, 32.80, 125.87, 126.25, 127.03, 127.10, 127.41, 127.55, 127.85, 127.97, 128.27, 128.61, 128.81, 130.54, 130.72, 131.72, 131.77, 132.19, 132.97, 133.14 ppm; ³¹P NMR (CDCl₃) δ = 7.94 ppm (m); Anal for C₁₇H₁₈BP Calcd: C 77.31, H 6.87. Found: C 77.41, H 6.93.
c-Hexylphenylphosphine-borane (2f). Yield 74%; ¹H NMR (CDCl₃) δ = -0.05-1.65 (br m, 3 H), 1.12-1.46 (m, 5 H), 1.63-2.10 (m, 6 H), 5.24 (dq, J _P-H = 364 Hz, 1 H), 7.42-7.77 (m, 5 H) ppm; ¹³C NMR (CDCl₃) δ = 25.61, 26.24, 26.29, 26.48, 26.52, 26.69, 28.18, 28.21, 32.99, 33.67, 124.11, 125.17, 128.60, 128.79, 131.37, 131.42, 133.20, 133.36 ppm; ³¹P NMR (CDCl₃) δ = 13.12 ppm (m); Anal for C₁₂H₂₀BP Calcd: C 69.94, H 9.78. Found: C 69.72, H 9.82.
i-Propylphenylphosphine-borane (2g). Yield 64%; ¹H NMR (CDCl₃) δ = -0.05-1.40 (br m, 3 H), 1.09-1.36 (m, 6 H), 2.16-2.39 (m, 1 H), 5.30 (dq, J _P-H = 364 Hz, 1 H), 7.42-7.60 (m, 3 H), 7.63-7.78 (m, 2 H) ppm; ¹³C NMR (CDCl₃) δ = 17.45, 17.99, 23.31, 24.01, 124.13, 125.19, 128.63, 128.82, 131.48, 133.19, 133.35 ppm; ³¹P NMR (CDCl₃) δ = 17.03 ppm (m); Anal for C₉H₁₆BP Calcd: C 65.12, H 9.71. Found: C 64.91, H 9.57.
Phenyl-p-tolylphosphineborane (2h). Yield 76%. ¹H NMR (CDCl₃) δ = 0.21-2.02 (br m, 3 H), 2.44 (s, 3 H), 6.34 (dq, J _P-H = 380 Hz, 1 H), 7.39-7.48 (m, 2 H), 7.43-7.79 (m, 7 H) ppm; ¹³C NMR (CDCl₃) δ = 21.50, 121.80, 122.93, 125.98, 127.12, 128.60, 128.80, 128.99, 129.39, 129.62, 129.83, 130.49, 130.54, 130.69, 130.72, 130.77, 131.34, 131.39, 131.51, 132.58, 132.76, 132.94, 142.06, 142.11 ppm; ³¹P NMR (CDCl₃) δ = 1.90 ppm (m); Anal for C₁₃H₁₆BP Calcd: C 72.95, H 7.53. Found: C 72.89, H 7.61.
Phenyl-o-tolylphosphine-borane (2i). Yield 18%; ¹H NMR (CDCl₃) δ = 0.23-2,00 (br m, 3 H), 2,42 (s, 3 H), 6,46 (dq, J _P-H = 380 Hz, 1 H), 7.25-7.80 (m, 9 H) ppm; ¹³C NMR (CDCl₃) δ = 20.97, 21.08, 125.31, 126.33, 126.56, 128.86, 128.91, 129.06, 130.93, 131.08, 131.32, 131.37, 131.91, 131.96, 132.61, 132.79, 134.13, 134.40, 141.62 ppm; ³¹P NMR (CDCl₃) δ = -3.83 ppm (m); Anal for C₁₃H₁₆BP Calcd: C 72.95, H 7.53. Found: C 72.88, H 7.61.
Di-c-Hexylphosphine-borane (2k). Yield 41%; ¹H NMR (CDCl₃) δ = -0.45-1.50 (br m, 3 H), 1.20-1.59 (m, 10 H), 1.64-2.02 (m, 12 H), 4.15 (dq, J _P-H = 348 Hz, 1 H) ppm; ¹³C NMR (CDCl₃) δ = 25.65, 26.21, 26.43, 26.63, 27.60, 28.48, 29.15, 29.21, 29.27 ppm; ³¹P NMR (CDCl₃) δ = 18.94 ppm (m); Anal for C₁₂H₂₆BP Calcd: C 67.95, H 12.35. Found: C 68.11, H 12.35.
Phenyl-i-propoxyphosphine-borane (2l). Yield 36%; ¹H NMR (CDCl₃) δ = 0.05-1.73 (br m, 3 H), 1,31 (t, 6 H), 4.45 (m, 1 H), 7.18 (dq, J _P-H = 400 Hz, 1 H), 7.47-7.68 (m, 3 H), 7.76-7.90 (m, 2 H) ppm; ¹³C NMR (CDCl₃) δ = 23.50, 73.38, 73.50, 128.75, 128.95, 131.79, 132.01, 132.54, 132.59 ppm; ³¹P NMR (CDCl₃) δ = 93.30 ppm (m); Anal for C₁₂H₂₆BOP Calcd: C 59.39, H 8.86. Found C 59.31, H 8.78.

15

Typical procedure for the reduction of secondary phosphine oxides with BH₃˙THF complex:
To a solution of secondary phosphine oxide (0.5 mmol) in 10 mL of dry THF was added water (about 5 mmol) and after homogenization of the reaction mixture 10 mmol of BH₃˙SMe₂ complex was added dropwise via syringe. The mixture was stirred at room temperature for 8 min-1.5 h (see Table [2] ). Then reaction mixture was evaporated to dryness and the crude product was purified by column chromatography (hexane:ethyl acetate 6:1).
Compounds data:
Di-p-anisylphosphine-borane (2o). Yield 73%. ¹H NMR (CDCl₃) δ = 0.15-1.87 (br m, 3 H), 3.87 (s, 6 H), 6.30 (dq, J _P-H = 380 Hz, 1 H), 6.93-7.05 (m, 4 H), 7.53-7.68 (m, 4 H) ppm; ¹³C NMR (CDCl₃) δ = 55.37, 114.55, 114.78, 134.38, 134.59 ppm; ³¹P NMR (CDCl₃) δ =-1.18 ppm (m); Anal for C₁₄H₁₈BO₂P Calcd: C 64.65, H 6.98. Found: C 64.54, H 6.89.
Di-(3,5-dimethyl)-phenylphosphine-borane (2p). Yield 70%. ¹H NMR (CDCl₃) δ = 0.15-1.88 (br m, 3 H), 2.37 (s, 12 H), 6.21 (dq, J _P-H = 380 Hz, 1 H), 7.16 (br s, 2 H), 7.27 (br s, 2 H), 7.33 (br s, 2 H) ppm; ¹³C NMR (CDCl₃) δ = 21.26, 130.30, 130.50, 133.27, 133.32, 138.60, 138.82 ppm; ³¹P NMR (CDCl₃) δ = 3.23 ppm (m); Anal for C₁₆H₂₁BP Calcd: C 75.03, H 8.66. Found: C 74.84, H 8.72.
1-Naphthylphenylphosphine-borane (2q). Yield 68%; ¹H NMR (CDCl₃) δ = 0.28-2.13 (br m, 3 H), 6.84 (dq, J _P-H = 380 Hz, 1 H), 7.37-7.74 (m, 8 H), 7.90-8.00 (m, 1 H), 8.00-8.19 (m, 3 H) ppm; ¹³C NMR (CDCl₃) δ = 121.79, 122.86, 125.05, 125.10, 125.18, 125.37, 125.55, 126.56, 126.67, 127.50, 128.87, 129.08, 129.22, 131.33, 131.37, 132.47, 132.67, 133.07, 133.12, 133.19, 133.47, 133.60, 134.81, 135.08 ppm; ³¹P NMR (CDCl₃) δ = -5,73 ppm (m); Anal for C₁₆H₁₆BP Calcd: C 76.84, H 6.45. Found: C 76.64, H 6.31.
[(2-Methyl)-1-naphthyl]phenylphosphine-borane (2r). Yield 20%; ¹H NMR (CDCl₃) δ = 0.20-1.95 (br m, 3 H), 2.71 (s, 3 H), 7.09 (dq, J _P-H = 386 Hz, 1 H), 7.32-7.56 (m, 5 H), 7.61-7.75 (m, 2 H), 7.80-7.98 (m, 3 H), 8.09-8.19 (m, 1 H) ppm; ¹³C NMR (CDCl₃) δ = 23.31, 23.47, 125.48, 125.68, 127.14, 127.56, 128.86, 128.91, 129.00, 129.06, 129.26, 129.44, 131.32, 131.37, 132.07, 132.19, 132.24, 132.83, 133.02 ppm; ³¹P NMR (CDCl₃) δ = -22,11 ppm (m).
Di-n-hexylphosphine-borane (2s). Yield 26%; ¹H NMR (CDCl₃) δ = -0.30-1.45 (br m, 3 H), 0.84-1.03 (m, 6 H), 1.22-1.51 (m, 13 H), 1.51-1.90 (m, 7 H), 4.57 (dq, J _P-H = 352 Hz, 1 H) ppm; ¹³C NMR (CDCl₃) δ = 14.02, 20.13, 20.84, 22.43, 24.38, 24.45, 30.27, 30.50, 30.93, 31.25 ppm; ³¹P NMR (CDCl₃) δ = -7.04 ppm (m); Anal for C₁₂H₃₀BP Calcd: C 66.68, H 13.99. Found: C 66.91, H 13.87.