Generation of Silylethynolates via C-Si Bond Cleavage of Disilylketenes Induced by t-BuOK [1]

Abstract

Disilylketenes undergo selective mono-desilylation upon treatment of t-BuOK in the presence of HMPA. The resulting silylethynolates are convertible to other disilylketenes in good yields. The intermediary silylethynolate was analyzed by NMR and IR spectroscopy.

Key words

disilylketene - silylethynolate - potassium t-butoxide - carbon-silicon bond cleavage - HMPA

1

Presented in part at the 70th Annual Meeting of the Chemical Society of Japan, Tokyo, March 1996, Abstr. 2J392.

References

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• 7 Recently, Ishikawa and co-workers reported (Me₃Si)₃SiLi undergoes nucleophilic attack onto the silicon center of 1a in THF, but their attempts to trap the resulting silylethynolate were unsuccesful: Naka A. Ohshita J. Kunai A. Lee ME. Ishikawa M. J. Organomet. Chem.  1999,  574:  50 
• 8a n-BuLi is known to react with 1a at the ketene sp-carbon in the absence of HMPA: Ponomarev SV. rman MB. Lebedev SA. Pechurina SY. Lutsenko IF. Zh. Obsh. Khim.  1971,  41:  127 
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• Analytical data for 2:
• 9a

  1,1-Bis(trimethylsilyl)-2-[(1,1-dimethylethyl)dimethylsilyl]oxy-2-phenylethene (2, R = Ph). ¹H NMR (CDCl₃) δ: -0.31 (s, 9 H), -0.29 (s, 6 H), 0.25 (s, 9 H), 0.86 (s, 9 H), 7.18-7.29 (m, 5 H); ¹³C NMR (CDCl₃) δ: -3.1, 2.1, 2.4, 18.6, 26.3, 109.9, 127.8, 128.0, 129.6, 142.0, 165.9. Anal. Calcd for C₂₀H₃₈OSi₃: C, 63.42; H, 10.11. Found: C, 63.31; H, 10.35.

• 9b

  1,1-Bis(trimethyl-silyl)-2-[(1,1-dimethylethyl)dimethylsilyl] oxy-1-propene (2, R = Me). This compound was not obtained in pure form and thus only ¹H and ¹³C NMR spectral data were shown.
  ¹H NMR (CDCl₃) δ: 0.12 (s, 9 H), 0.14 (s, 9 H), 0.20 (s, 6 H), 0.95 (s, 9 H), 2.03 (s, 3 H); ¹³C NMR (CDCl₃) δ: -2.3, 0.1, 2.7, 2.9, 19.1, 26.5, 107.1, 164.5.

• 10 Rathke’s report on the isolation of 1a by warming a THF solution of lithio t-butyl bis(trimethylsilyl)acetate to 25 °C may indicate that the eliminated t-BuOLi does not undergo C-Si bond cleavage of 1a under their condition: Sullivan DF. Woodbury RP. Rathke MW. J. Org. Chem.  1977,  42:  2038 
• 11a

  General Procedure for the Preparation of Disilylketenes using t -BuOK: Preparation of [(1,1-dimethylethyl)dimethylsilyl](trimethylsilyl)ketene(1b) from 1a is representative. Disilyllketene 1a (296.5 mg, 1.59 mmol) was dissolved in THF (1.6 mL) and HMPA (0.28 mL, 1.61 mmol). To the resulting yellow solution was added a solution of t-BuOK (180.0 mg, 1.60 mmol) in THF (3.2 mL) at 0 °C. The mixture was stirred for 1 h at the same temperature and quenched by t-BuMeSiOTf (0.37 mL, 1.61 mmol). After stirring the resulting solution for 2 h at room temperature, the reaction mixture was diluted with pentane and washed with water. Then the organic layer was dried by Na₂SO₄ and filtered through Florisil. Evaporation of the solvent followed by silica-gel chromatography (Wakogel C-200) afforded 1b as a colorless oil (305.4 mg, 84% yield).

• 11b

  We were unable to detect the formation of any
  O-silylated product (silyl silylethynyl ether) under these conditions. See ref. [13c] .

• 11c

  The use of carbon electrophiles (MeI, Me₂SO₄, Me₃OBF₄, or PhCHO) instead of R₃SiX resulted in the formation of intractable mixtures under similar conditions.

• Analytical data for new disilylketenes (silicon-attached quarternary carbon was not observed in ¹³C NMR spectra):
• 12a

  (Dimethylphenylsilyl)(trimethylsilyl)ketene(1d). ¹H NMR (CDCl₃) δ: 0.14 (s, 9 H), 0.52 (s, 6 H), 7.40-7.43 (m, 3 H), 7.59-7.63 (m, 2 H); ¹³C NMR (CDCl₃) δ: -0.2, 1.2, 127.8, 129.4, 133.6, 138.3, 166.9; IR(neat) 2084 cm^-1 (CCO); MS (70 eV) m/z 248 (M⁺); bp 62-70 °C (0.05 mmHg). Anal. Calcd for C₁₃H₂₀OSi₂: C, 62.84; H, 8.11. Found: C, 63.10; H, 8.28.

• 12b

  Bis(triphenylsilyl)ketene(1k). ¹H NMR (CDCl₃) δ: 7.21-7.49 (m, 30 H); ¹³C NMR (CDCl₃) δ: 127.7, 127.8, 129.7, 129.8, 133.7, 135.2, 135.4, 135.9, 166.2; IR(nujol) 2080 cm^-1 (CCO); MS (70 eV) m/z 558 (M⁺); mp 165-166 °C. Anal. Calcd for C₃₈H₃₀OSi₂: C, 81.67; H, 5.41. Found: C, 81.40; H, 5.32.

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• 15b

  We suppose that HMPA may coordinate onto the smaller silicon center of the disilylketene to form a penta-coordinate silicate, and facilitate the alkoxide-induced Si-C bond cleavage.

1

Presented in part at the 70th Annual Meeting of the Chemical Society of Japan, Tokyo, March 1996, Abstr. 2J392.

2

Deceased Oct. 4, 1995. Address all correspondence to Dr. Masato Ito, Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552, Japan; E-mail: [e-mail].