Bis phenyldimethylsilyl cuprate

To a stirred suspension of NaH or KH (20 mmol) in HMPA (CAUTION— CANCER SUSPECT AGENT) was added hexamethyldisilane (10 mmol) slowly with stirring. A clear yellow-brown solution of trimethylsilyl potassium was obtained immediately mild heating at 30-40 °C is necessary to prepare trimethylsilylsodium. 

Dime thy Iphenylsilyl chloride (10 mmol) was stirred with lithium (30 mmol, Fison s shot ) in THF (25 ml) at -8°C for 36 h. The red solution is stable for several weeks at —20°C. 

This reagent is perhaps best thought of as a higher-order mixed cuprate of the type (R3Si)2Cu(CN)Li2 (7). 

To a stirred slurry of copper(i) cyanide (110 mmol) in THF (100 ml), cooled to 0 °C, was added a solution of dimethylphenylsilyl lithium (220 mmol, 1.3m in THF), and the mixture was stirred at 0°C for a further 30min. After cooling to -78 °C, a solution of methyl cinnamate (100 mmol) in THF (50 ml) was added, and stirring was continued at -78 °C for 6 h. At this time, iodomethane (300 mmol) (CAUTION—CANCER SUSPECT AGENT) was added, and the mixture allowed to warm to ambient temperature with 

The crude product was dissolved in MeOH (400 ml), and water (100 ml) and LiOH (313 mmol) were added. The two-phase mixture was heated under reflux for 24 h, and then concentrated in vacuo to a volume of 100ml. Ether (300 ml) and water (200 ml) were added, and the separated organic phase was washed with aqueous LiOH (2 x 100 ml, 6 m). The combined basic extracts were acidified to pH 2 using concentrated sulphuric add, and then extracted with ether (5 x 100 ml). The combined organic extracts were washed with water and brine, and dried. Concentration in vacuo followed by crystallization (pentane acetone, 5 1) gave the acid (59 mmol, 59%) as white prisms, m.p. 98-99°C. 

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A solution of hex-l-yne (4.5 mmol) in THF (1ml) was added slowly to lithium bis(phenyldimethylsilyl)cuprate (Chapter 8) (5 mmol, based on CuCN) at 0°C, and the mixture was stirred for 15min at 0°C. Saturated ammonium chloride solution (1 ml) was added, and stirring was continued for 5 min at 0°C. Light petroleum was then added, and the organic layer was washed with ammonium chloride solution, and dried. Concentration and chromatographic purification on silica gel gave the vinylsilane (4.23 mmol, 94%). 

Lewis acids, 15,72,106,108-11,112,116,128 Lithiation, 84 reductive, 68 o-Lithiation, 40 a-Lithiosilanes, 65, 68 o-Lithiosilyl enol ethers, 77 a-Lithiovinylsilanes, 69 Lithium bis(phenyldimethylsilyl)cuprate, 8,53... 

The conjugate addition of lithium bis(phenyldimethylsilyl)cuprates to tt./t-unsaUi rated esters forms enolates, which readily react with aldehydes to give 2-substituted 3-silyl esters (equation 129)509. The products are useful as intermediates in the synthesis of allylsilanes and natural products. Yields of this reaction may be significantly increased by... 

Fleming has generated enolates by conjugate addition of lithium bis(phenyldimethylsilyl)cuprate to a,p-unsaturated esters. The intermediate (Z)-enolates undergo stereoselective aldol addition, providing adducts having three contiguous stereocenters one example of this process is seen in equation (20). - ... 

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