[57519-88-7]  · C9H14Cl2Si2  · 1,1-Dichloro-2,2,2-trimethyl-1-phenyldisilane  · (MW 249.29)

(silylating agent for p-allylpalladium complexes1 and palladium-catalyzed allylic silylation, giving allylsilanes;2 for asymmetric 1,4-disilylation of a,b-unsaturated ketones, giving optically active b-hydroxy ketones after oxidation3)

Physical Data: bp 50-60 °C/0.5 mmHg.

Solubility: sol THF, benzene.

Form Supplied in: oil, with some 1-chloro-2,2,2-trimethyl-1-phenyldisilane.2

Analysis of Reagent Purity: NMR, MS.

Preparative Method: the disilane is prepared in 75% yield by selective chlorodephenylation of 2,2,2-trimethyl-1,1,1-triphenyldisilane with Hydrogen Chloride in the presence of a catalytic amount of Aluminum Chloride in benzene.2,4

Purification: fractional distillation.

Handling, Storage, and Precautions: the disilane reacts with air and water, and should be kept sealed to preclude decomposition. The reagent is a potential acidic corrosive. It should be handled in a well ventilated hood.

1,4-Disilylation of a,b-Unsaturated Ketones.

In the presence of palladium-phosphine catalysts such as Tetrakis(triphenylphosphine)palladium(0), the unsymmetrically substituted disilane PhCl2SiSiMe3 reacts with a,b-unsaturated ketones in refluxing benzene to give g-(phenyldichlorosilyl) silyl enol ethers, which can be converted into b-(phenyldiethoxysilyl) ketones by treatment with ethanol and Triethylamine (eq 1).3 Oxidation of the phenyldiethoxysilyl group with Hydrogen Peroxide in the presence of fluoride gives b-hydroxy ketones in high yields. g-(Phenyldimethylsilyl) lithium enolates, generated by treatment of the g-(phenyldichlorosilyl) silyl enol ethers with Methyllithium, undergo alkylation with alkyl halides to give b-(phenyldimethylsilyl)-a-alkyl ketones with high anti selectivity (eq 2). These b-(phenyldimethylsilyl) ketones are subjected to fluorodephenylation followed by oxidation to give anti-b-hydroxy-a-alkyl ketones. The 1,4-addition of the disilane is enantioselective when catalyzed by PdCl2[(R)-BINAP], thereby providing optically active anti-b-hydroxy-a-alkyl ketones with 66-92% ee (Table 1).3a

Silylation of p-Allylpalladium Complexes and Palladium-Catalyzed Allylic Silylation.

The disilane is a highly reactive reagent for the silylation of p-allylpalladium complexes, producing phenyldichloro(allyl)silanes in high yields.1 The retention of configuration observed in the silylation of an optically active p-allylpalladium complex indicates that the silylation occurs by way of a p-allyl(phenyldichlorosilyl)palladium intermediate (eq 3). Palladium-catalyzed allylic silylation of allylic chlorides is also effected with the disilane reagent. In the presence of 1 mol % of palladium catalyst coordinated with triphenylphosphine or 1,1-Bis(diphenylphosphino)ferrocene (dppf), the silylation gives allylsilanes in high yields (eq 4).2 The functionalized allylsilanes may be oxidized to allylic alcohols.

1. Hayashi, T.; Yamamoto, A.; Iwata, T.; Ito, Y. CC 1987, 398.
2. Matsumoto, Y.; Ohno, A.; Hayashi, T. OM 1993, 12, 4051.
3. (a) Hayashi, T.; Matsumoto, Y.; Ito, Y. JACS 1988, 110, 5579. (b) Hayashi, T.; Matsumoto, Y.; Ito, Y. TL 1988, 29, 4147. (c) Matsumoto, Y.; Hayashi, T.; Ito, Y. T 1994, 50, 335.
4. Hengge, E.; Bauer, G.; Brandstätter, E.; Kollmann, G. M 1975, 106, 887.

Tamio Hayashi

Hokkaido University, Sapporo, Japan

Wesley K. M. Chong

Agouron Pharmaceuticals, San Diego, CA, USA

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