Acyl derivatives carbon-silicon bonds

Reductive cleavage of the carbon-silicon bond of acyl silanes, including a-alkoxy and t/./i-dialkoxy derivatives, to give aldehydes may be accomplished by palladium-catalysed hydrogenolysis at ambient temperature and pressure212. 

Three types of products have been observed in intermolecular acylations of homoallylic silanes, the major one being cyclopropylmethyl ketones, along with minor amounts of 3-butenyl ketones and -chlo-ro ketones. It is likely that all derive from the carbenium ion formed by acylation of the double bond, which then undergoes cyclodesilylation or hydride transfer followed by 3-elimination (Scheme 14). The former leads to the cyclopropane, which can ring open to give the chloro products. The latter pathway gives the butenyl ketone, and is supported by location of substituent positions on methylated substrates. However, the direct acylation of the carbon-silicon bond should not necessarily be excluded in consideration of more general cases. Titanium tetrachloride seems the preferred catalyst in these cyclodesilyl-ations, and low temperatures minimize the formation of the chloro by-products. Intramolecular versions... 

TetraaUcylsilanes are stable compounds. Therefore, it is necessary to activate the compounds for the conpling reaction. Since dialkylsilacyclobutanes have high strain energy, palladium complexes can easily insert into the carbon-silicon bond oxidatively, and the resultant complexes conple with acyl chlorides to give l-sila-2-oxa-3-cyclohex-ene derivatives (Scheme 14). 

Carbon monoxide insertion into zirconium(IV)-silicon bond has been reported . The trimethylsilyl derivative Zr(/7 -C5H5)2(SiMe3)Cl was carbonylated under CO pressure (about 7 atm) in diethyl ether, giving the following silyl-acyl compound ... 

The organometallic compounds prepared from alkali metal derivatives of metal carbonyls include compounds in which a transition metal of a metal carbonyl residue is cr-bonded to another atom such as a carbon atom in an alkyl, acyl, aryl, or perfluoroalkyl group, to the heavier congeners of carbon —silicon, germanium, tin, and lead—to mercury and gold which form unusually stable compounds, and even to other transition metals. The preparation and properties of all of these classes of compounds will be considered and, for the sake of completeness, a few related compounds prepared by routes other than those involving anionic metal carbonyl derivatives will be discussed. 

Transition metal-catalyzed silicon-based cross-coupling reaction has emerged as a versatile carbon-carbon bond-forming process with high stereocontrol and excellent functional group tolerance [35], For example, (a-benzoyloxy)alkenylsilanes 105, prepared as a pure -isomer by 0-acylation of a lithium enolate derived from the corresponding acylsilane, reacts with carboxylic acid anhydrides in the presence of [RhCl(CO)2]2, giving rise to a-acyloxy ketones 106, which are then converted into 1,2-diketones by acidic workup (Scheme 5.27) [36]. 

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