Organosilicon reagents

Since silicon is more electropositive than carbon (see Table 7.1), the carbon-silicon bond is polarized in the direction Si -C. This polarization has two important 

The Si -C polarization supports the formation or development of carbocations in the P-position, a stereoelectronic phenomenon known as the This is com- 

Second-row elements such as silicon are known to stabilize a-carbanions with considerably greater effectiveness than their first-row counterparts. Early rationalization of this phenomenon favored the p j-d model B as a source of the stabilizing influence. More recently, stabilization by means of the high polarizability of Si and the presence of an empty o orbital on the silicon have been proposed. Overlap with the filled orbital of a flanking carbanionic center as in C can account for the observed stabilization.  

Alkynylsilanes are readily accessible by metalation of terminal alkynes, followed by addition of the appropriate trialkylchlorosilane. 

Reactions of alkynylsilanes with electrophiles in the presence of a Lewis acid catalyst such as BF3, AICI3, or TiCl4 generally occur regioselectively at the silicon-bearing carbon, due to the [3-effect, and under mild conditions. 

Catalyst = (PPh2)4Ni from Ni acac)2/PPh3/Bu 2AIH or PPh3)2PdCl2andBu 2AIH 

The silicon analogs of tfie tin reagents are less toxic, but are also less reactive. Yet, Hiyama showed ihatsilicon reagents imdergo cross-coupling reactions in ffiepresenceof added fluoride 

CHAPTER 19 transition METAL-CATALYZED COUPLING REACTIONS 

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Transfomations of cyclic acetals and their heteroanalogs under the action of organosilicon reagents 97MI1. 

P. Magnus, Organosilicon reagents for carbon-carbon bond-forming reactions, Aldrichimica Acta 13,43 (1980). 

M. Lalonde and T. H. Chan. Use of organosilicon reagents as protective groups in organic synthesis. Synthesis 817 (1985). 

Arylsilanols, silanediols, and triols performed poorly under fluoride activation conditions, but instead required Ag20 (78X274 However, the cross-coupling of arylsilanediols and similar organosilicon reagents (formed in situ from the respective halosilanes) can be achieved under very mild conditions, using phosphine-free catalysts in water in the absence of any organic cosolvents.275... 

Among other organosilicon reagents used for cross-couplings, notable ones are commercial vinylsiloxanes, which are useful for vinyl-transfer reactions (81).280... 

Evans, D.A., Hurst, K.M., Truesdale, L.K., and Takacs, J.M., The carbonyl insertion reactions of mixed tervalent phosphorus-organosilicon reagents, Tetrahedron Lett., 2495, 1977. 

The wide spectrum of Organosilicon Reagents now available can be used to ... 

One of the earliest synthetic uses of organosilicon reagents was the silicon equivalent of writing reaction called Peterson Reaction. 

As already seen the use of organosilicon reagents for organic synthesis and as intermediates to be discussed later is now becoming a field of great importance. 

Not only organoboron reagents but also organosilicon reagents are suitable nucleophiles in the rhodium-catalyzed asymmetric 1,4-additions to a,p-enones in... 

Reactions with Organosilicon Reagents The Hiyama Reaction... 

Reaction with Organosilicon Reagents (Hiyama Coupling) 668... 

Recent synthetic applications of organosilicon reagents of alkenes (equation 30). 

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