Carbon-tin bond

The silyl and stannyl substituents are crucial to these reactions in two ways. In the electrophilic addition step, they act as electron-releasing groups promoting addition and also control the regiochemistry. A silyl or starmyl substituent strongly stabilizes carboca-tion character at the /3-catbon atom and thus directs the electrophile to the a-carbon. The reaction is then completed by the limination step, in which the carbon-sihcon or carbon-tin bond is broken. 

Photoelectron spectroscopy shows that the carbon-tin bond prefers that orientation in which it lies parallel to the pir orbitals of the double bond, to permit carbon-metal hyperconjugation (146). 

Organotin compounds are characterized by the presence of a carbon-tin bond and have the following general formula ... 

Peddle and Redl,0) were still rather pessimistic in 1970 Thus while it should be possible to resolve an optically active organotin compound with four carbon-tin bonds, it seems unlikely that such a compound would be very useful in investigating the stereochemistry of substitution at the tin atom 10). 

The problems associated with the use of this classical method in organotin chemistry are essentially due to the fact that the carbon-tin bond can sometimes very easily be cleaved by electrophiles or by nucleophiles. The crucial step is therefore the elimination of the auxiliary group without the cleavage of any of the carbon-tin bonds. This cleavage could for instance not be achieved successfully in the case of /7-(z -propylmethylphenylstannyl)-N,N-dimethylaniline [formula (60) in... 

In contrast to silylcarbenes, the analogous stannylcarbenes 2p are not stable, which explains why they have attracted little interest. Their instability is probably due to the long carbon-tin bond, which does not allow sufficient steric protection of the carbene center. Their reactivity seems to be quite similar to that of stable (phosphino)(silyl)carbenes Cyclopropanation reactions have been reported with methyl acrylate as well as coupling reactions with tert-butyl isonitrile.73... 

Of great synthetic potential are demetallations with simultaneous formation of C-Sn bonds (Figure 2.20) [137,146,230,281,282]. These reactions presumably proceed via a heterobimetallic intermediate containing an Sn-M-C group. Reductive elimination of the metal M from this intermediate leads to formation of the carbon-tin bond. The resulting alkyl- or vinylstannanes are valuable synthetic intermediates. 

In 2000, Chamboumier and Gawley reported the failure of a conformationaUy locked 2-(tributylstannyl)piperidine to transmetalate when the 2-(tributylstannyl) moiety of a 4-fert-butylpiperidine is equatorial, Sn/Li exchange is facile, but when the 2-tributylstannyl group is axial, transmetalation fails (compare Figure 3d,i). In other words, in these conformationaUy rigid piperidines, there appears to be a configurational requirement for transmetalation the nitrogen atom lone pair has to be synclinal to the adjacent carbon-tin bond for transmetalation to succeed. 

The relative weakness of the carbon-tin bond provided a useful method for carbon-carbon bond formation by cross-coupling reaction with acyl halides. This reaction has been applied for the two-step synthesis of a-ketocyclopropyl sulfones (equation 8)30. 

Organometallic compounds possessing carbon-tin bonds can resist he action of TPAP during the oxidation of alcohols.99... 

Vinylsilanes react with boron trichloride to give the corresponding borodesilylation products in good yield which, in turn, can be transformed into boronic esters 124 by alcoholysis (equation 102). The initial dichloroorganoborane products can be used directly in the Suzuki-Miyaura cross-coupling reaction192. Replacement of a carbon-silicon bond by a carbon-tin bond in fluorinated alkenes (e.g. 125) can be achieved by the reaction of silanes with Bu3SnCl and KF in DMF under mild conditions (equation 103)193. It is... 

A number of conflicting reports exist on the stereochemical course of halogenolysis of carbon-lithium and carbon-tin bonds when the carbon atom undergoing substitution is part of an alicyclic ring. Halogenolysis of optically active 1-methyl-... 

The reaction is supposed to start with oxidative addition of an electrophilic component to Pd(0) species. Shirakawa and Hiyama demonstrated the possibility of oxidative addition of carbon-tin bond to palladium(O) to drive the catalytic cycle [32], that was suggested without evidence by Stille [33]. 

First, the utility of organostannyl compounds for generating carbo-cations or carbon radicals is discussed. Oxidation of organostannyl compounds such as a-stannyl sulfides, amines, esters, and ethers with metallic oxidants or photochemical methods gives their cation radicals, from which carbocations and carbon radicals are generated by cleavage of the carbon-tin bond. These reactive intermediates are employed for carbon-carbon bond formation, particularly in intermo-lecular reactions. 

The radical chemistry of organotins is undoubtedly dominated by tin hydride chemistry, which has been at the source of radical chain reactions of valuable interest for organic synthesis. However, the demonstration of the ability of allyltin reagents to undergo homolytic cleavage of the carbon-tin bond goes back to the early and only ten years... 

In organic syntheses allylsilanes and allylstannanes have been used extensively as allyl anion equivalents during the last two decades [187-190]. The regioselective attack of electrophiles, which finally yields products with allylic inversion (Scheme 43), has been explained by the hyperconju-gative stabilization of carbenium centers by the carbon-silicon or carbon-tin bond in the j3-position [191-196], which has initially been derived from solvolytic experiments [197-199]. 

Reactions of tin(IV) halides or organotin halides with organic derivatives of more electropositive metals provide the most important general synthetic routes to carbon-tin bonds (equation 6). The most frequently used R -M compounds are those of magnesium and lithium, with sodium, zinc, and aluminum having a more limited use. Some examples of these reactions are given in equations (7-9). 

Reactions of RsSnM (M = Li, Na, MgX, or Cu) occur with various organic electrophiles, e.g. organic halides and tosylates, aldehydes and ketones, /i-enones, and epoxides, to give new carbon-tin bonded compounds. 

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