Asymmetric Hydrosilylation of Alkenes with Alkoxyhydrosilanes Catalyzed by Chiral Bis(oxazolinyl)phenyl-Rhodium Complex

Yasunori Tsuchiya; Hirofumi Uchimura; Kazuki Kobayashi; Hisao Nishiyama

doi:10.1055/s-2004-831312

LETTER

Asymmetric Hydrosilylation of Alkenes with Alkoxyhydrosilanes Catalyzed by Chiral Bis(oxazolinyl)phenyl-Rhodium Complex

Yasunori Tsuchiya, Hirofumi Uchimura, Kazuki Kobayashi, Hisao Nishiyama*
Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan
Fax: +81(52)7893209; e-Mail: hnishi@apchem.nagoya-u.ac.jp;

Abstract

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Abstract

Asymmetric addition of alkoxyhydrosilanes to styrene derivatives was examined with chiral bis(oxazolinyl)phenyl-rhodium complex to give moderate ratios (up to 77:23) of α- and β-adducts and high enantioselectivity (up to 95% for the α-adduct).

Key words

rhodium - bisoxazoline - styrene - hydrosilylation - asymmetric catalysis

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References

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Typical Procedure for the Hydrosilylation of Styrene and Diethoxymethylsilane with Rh(Phebox- ip )Cl ₂ ₍ H ₂ O) (Run 2, Table 1): To a solution of the rhodium complex 1 (4.9 mg, 0.01 mmol) and styrene (104 mg, 1.00 mmol) in toluene (1 mL) was added diethoxymethylsilane (134 mg, 0.12 mmol) at r.t. The mixture was stirred at 50 °C for 72 h and was concentrated to give an oily residue, which was purified by silica-gel column chromatography to give a mixture of α- and β-silylated products (3a and 3b, 224 mg, 94%). The ratio of 54:46 was determined by ¹H NMR. The mixture (224 mg, 0.94 mmol) was treated with excess of KF, K₂CO₃, and H₂O₂ (30%, 1 mL) in THF-MeOH (1:1, 2 mL) at 0 °C. The mixture was stirred for 12 h and was treated with sat. aq solution of Na₂S₂O₃ (6 mL) for 1 h. After usual work-up of extraction and concentration, the residue was purified by column chromatography to give a mixture 1- and 2-phenylethanol (110 mg). The ee of 1-phenylethanol was determined by HPLC with DAICEL CHIRALCEL OB (i-PrOH-hexane = 1:9, 0.5 mL/min); 96:4, 11.4 min. for S and 14.6 min for R. For run 4 with AgBF₄, the procedure is as follows: a suspension of the rhodium complex 1 (0.01 mmol) and AgBF₄ (0.02 mmol) in THF (1 mL) was stirred for 1 h. Then the solvent was removed under reduced pressure to give the corresponding cationic complex as solids followed by addition of solvent, alkene, and the silane.

We did not observe formation of simple reduction products of alkenes or vinylsilanes derived from ‘silylrhodation-β-hydride elimination’ in most cases.