Organosilicon compounds preparation

Some organosilicon compounds undergo transmetallation. The allylic cyanide 461 was prepared by the reaction of an allylic carbonate with trimethylsi-lyl cyanide[298]. The oriho esters and acetals of the o. d-unsaturated carbonyl compounds 462 undergo cyanation with trimefhylsilyl cyanide[95]. 

The possibility of the existence of organosilicone compounds was first predicted by Dumas in 1840, and in 1857 Buff and Wohler found the substance now known to be trichlorosilane by passing hydrochloric acid gas over a heated mixture of silicone and carbon. In 1863 Friedel and Crafts prepared tetraethylsilane by reacting zinc diethyl with silicon tetrachloride. 

Fluorinated organosilicon compounds may be prepared from readUy available fluorohalocarbons by using phosphorous amides [84, 85, 86] or tetrakis(dimeth-ylamino)ethylene [57] for the generation of the fluoroorganic nucleophiles (equations 61-69). 

To prepare multifunctionalized symmetric organosilicon compounds by the polyalkylation of benzene. (2-chloroethyi)trichlorosilane and (3-chloropropyl)tri-chlorosilane were reacted with benzene. Polyalkylations of benzene with (2-chloroethyl)silane and (3-chloropropyl)silane were carried out in the presence of aluminum chloride catalyst at a reaction temperature of 80 C. The reaction of benzene with excess (2-chloroethyI )trichlorosilanes afforded pcralkylated product, hexakis(2-(trichlorosilyl)ethyl)benzene in good yield (70%). ... 

Alkyllead-substituted organosilicon compounds can be prepared as follows193 ... 

Several methods, similar to those used to produce organosilicon compounds, are available for the preparation of germanium organyls. Organogermanium halides, which are the source of practically all other types of germanium organyls, can be formed by the direct reaction of aryl and alkyl halides with Ge/Cu alloys (equation 1). 

During the last three decades, a number of organosilicon compounds have been prepared which have opened new vistas in the synthesis of numerous organic compounds and have brought to light many fascinating reactions. 

In 1976 W.C. Still (J. Org. Chem. 41, 3063-41) discovered Me3SiLi and in the same year RB. Dervan and MA Shippey (J. Awer Chem. Soe, 98, 1265-1267, 1976) discovered Me3SiK which are silicon nucleophiles and both of which promised to be very useful for preparing organosilicon compounds. 

An alternative method for preparing metallocenyllithium derivatives, convertible into organosilicon compounds, is based on cleavage of organomercury compounds with organolithium reagents. It was used for the silylation of ferrocene (113, 151) ... 

The study of the antitumorous effect of low-toxic silatranes not affecting healthy organs and tissues and producing a certain antiblastic effect in the tests with animals indicates the necessity of further investigation of this class of organosilicon compounds in order to develop a new type of anti-cancer preparations. 

Since 1989, when the first volume of The Chemistry of Organosilicon Compounds appeared1, large strides have been made in preparing silicenium cations. The first X-ray structures2,3 of solvent stabilized silicenium cations are among the most notable successes. Most recently, a free silicenium cation has been prepared in solution4 5. In addition... 

This short review deals with the topical subject chirality in bioorganosilicon chemistry . Two different aspects will be discussed (i) biological recognition of enantiomeric organosilicon drugs and (ii) biocatalysis as a method for the preparation of optically active organosilicon compounds . Most of the experimental material described in this article (which does not lay claim to completeness) comes from our own laboratory. 

III. BIOCATALYSIS AS A METHOD FOR THE PREPARATION OF OPTICALLY ACTIVE ORGANOSILICON COMPOUNDS... 

Enantioselective enzymatic amide hydrolyses can also be applied for the preparation of optically active organosilicon compounds. The first example of this is the kinetic resolution of the racemic [l-(phenylacetamido)ethyl] silane rac-84 using immobilized penicillin G acylase (PGA E.C. 3.5.1.11) from Escherichia coli as the biocatalyst (Scheme 18)69. (R)-selective hydrolysis of rac-84 yielded the corresponding (l-aminoethyl)silane (R)-85 which was obtained on a preparative scale in 40% yield (relative to rac-84). The enantiomeric purity of the biotransformation product was 92% ee. This method has not yet been used for the synthesis of optically active silicon compounds with the silicon atom as the center of chirality. 

Enantioselective enzymatic esterifications represent a further type of biotransformation that has been used for the synthesis of optically active organosilicon compounds. The first example of this particular type of bioconversion (kinetic racemate resolution) is illustrated in Scheme 22. Starting from the racemic l-silacyclohexan-2-ol rac-43, the optically active 5-phenylpentanoate (S)-94 was prepared by enantioselective esterification with 5-phenylpentanoic acid using 2-methylheptane as solvent and crude Candida cylin-dracea lipase (CCL E.C. 3.1.1.3) as biocatalyst7. The enantiomeric purity of (S)-94 was ca 65% ee (bioconversion not optimized). 

Most organosilicon compounds (silyl ethers, silylenolethers, allyl- and vinyl-silanes) are stable enough to be easily prepared, handled and stored with a minimum of precautions. Whilst silyl ethers are mainly considered as protected alcohol... 

The first preparation of such an alkali-organosilicon compound was made by Kraus391 and Benkeser31. Gilman and Wu224 first cleaved hexaphenyl-disilane with potassium/sodium alloy and obtained triphenylsilyl potassium as a dark solution in ether. 

These syntheses of all three elements have been widely used — those of organoboron compounds often as a prelude to further transformations (see Section 15.4, Ref. [1]), those of organosilicon compounds often to characterize organomagnesium reagents, and those of organophosphorus compounds often to prepare phosphine ligands. 

Substitution by Alkyls of Zinc, Mercury, and Aluminum. The reaction of alkyls of zinc with ethyl silicate or silicon tetrachloride was the first to be used for the preparation of organosilicon compounds. During the period 1863 to 1880 Friedel and Crafts and later Ladenburg employed zinc dimethyl and zinc diethyl to prepare the corresponding alkyls of silicon and many of the intermediate substitution products as well. The reactions were conducted in sealed tubes heated to about 160° and were of a straightforward metathetical type ... 

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