Silanes palladium catalysed synthesis

Palladium-mediated addition of silyl stannane reagents to alkynyl ethers has been employed for the synthesis of aliphatic acyl silanes in very good yields via the intermediate a-alkoxy-/J-stannyl vinyl silanes (enol ethers of acyl silanes)82. In a second palladium-catalysed step, the vinyl stannane moiety could be coupled to suitable halides before hydrolysis to the acyl silanes with trifluoroacetic acid (Scheme 11). 

Hi. Carbon-silicon bonds. Following the earlier reports mentioning the palladium-catalysed addition of organosilylstannanes to alkynes or isonitriles , Mori and coworkers realized tandem transmetallation-cyclization reactions with bifunctional halogeno triflates and Bu3SnSiMe3 18. The reactivity of 18 under palladium catalysis was used for the silylstannylation of alkenes or the synthesis of allylic silanes via a three-component (aryl iodide - - diene - - 18) coupling reaction. Recently, a similar... 

The heteroaryl derivatives of boron, silicon, and tin, which show related patterns of reactivity, have found considerable application in synthesis. Unlike lithium compounds, they are generally fairly stable to air and water but will undergo a range of selective reactions under relatively mild conditions. Heteroaryl boronic acids and stannanes are particularly useful as the organometallic component in palladium-catalysed coupling reactions (section 2.7.2.2) heteroaromatic silanes such as 2-... 

Among the applications of allyl silanes reported this year their reaction with phenylselenyl chloride and subsequent oxidation of the resulting allyl selenides to allylic alcoholshas been used in the sequence outlined in Scheme IS. 3-Bromoallyltrimethylsilane therefore behaves as a hydroxypropenyl synthon. Nitroalkenes react with allylsilanes to give, after hydrolysis, y,S-unsaturated ketones, and a synthesis of substituted cyclopentenones based on this procedure has been described.Allyl trimethylsilyl ethers undergo a palladium-promoted coupling with aryl iodides to give /3-aryl-a,/3-unsaturated ketones, and palladium also catalyses the reaction of various aryl bromides with trimethylsilyl acetylene to produce ethynylated aromatics. 

Asymmetric hydrosilylation of alkenes, catalysed by ferrocenylphosphine-palladium complexes, can be utilized in a synthesis of optically active alcohols from alkenes (Scheme 1). The initial optically active silane adducts are converted to alkyl pentafluorosilicates (1) which are then cleaved oxidatively, with retention of configuration, using peracid (c/. 3,132). Complex (2) was the best of several hydrosilylation catalysts examined using this, alcohols with enantiomeric purities of approx. 50% were obtained from norbornene and styrene as the alkenes. 

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