Silyl/stannyl exchange

Selective silyllstannyl exchange. Regioselective aldol condensation of methyl ketones can be effected by generation of the a-stannyl derivative via silyl-stannyl exchange... 

Mixed trialkylstannyl and silyl derivatives have also been used in coupling reactions, with subsequent replacement of the silyl substituent by bromine, leading to species that are capable of undergoing further coupling reactions. This process was amply demonstrated by the recent synthesis of micrococcinic acid 203, which involved four palladium-catalyzed crosscoupling reactions on stannylated substrates, two palladium-catalyzed trimethylstannane replacements of bromine, two trimethylsilyl displacements by bromine, and a total of four bromine-lithium exchange reactions, on three different thiazole derivatives and one pyridine derivative (91-TL4263). 

When Me3SiSnBu3 is treated with CsF, the fluoride anion should coordinate to the silyl group and not the stannyl group to produce a hypervalent silicate, and as a result, a stannyl anion would be generated.282 The stannyl anion reacts with vinyl iodide to produce a vinyl anion via a halogen-metal exchange and it reacts with the carbonyl group intramolecularly (Equation (113)). Aryl halides or allyl halides are also used in similar cyclizations.283,284... 

Methyl trimethylsilyl tellurium and phenyl trimethylsilyl tellurium exchanged the organyltelluro group for halogen in reactions with silyl, germyl, stannyl and plumbyl halides2. 

Trialkylsilyl- or stannyl-substituted carbenes 2 and 3 can be generated from the title compounds by a-elimination of hydrogen halide (HX) or metal halide, and silyl- or stannylcyclopropanes can be formed by intra- or intermolecular carbene transfer to C C bonds. To this end, 1-haloalkyl(trialkyl)metal compounds can be treated with sodium (Method A, metal halide exchange followed by base-induced a-elimination of HX) or with a strong base (Method B, a-elimination of HX), and l,l-dihaloalkyl(trialkyl)metal compounds can be treated with an al-kyllithium compound (Method C, metal/halide exchange and subsequent a-elimination of a metal halide). 

Finally, a method of generating enol stannyl ethers in situ is to start from enol silyl ethers by an exchange reaction with tributyltin fluoride. An example is given in Scheme 29. It has been reported that this process occurs preferentially at the less-substituted enol silyl ether site if several are available. ... 

Borabicyclo[3.3.1]nonane (9-BBN) has found use in the selective hydro-boration of alkenes in the presence of other reducible functional groups and its reaction with alkynylstannates has been studied. o-Stannyl- and a-silyl-substituted crotyl-9-BBN show promise as reagents for the stereo-regulated synthesis of acyclic systems. A series of papers covers the question of olefin-alkyl exchange in. 5-alkyl-9-BBN s, " the kinetics of reduction of substituted benzaldehydes with 9-BBN, and the kinetics and mechanism of hydroboration of alkynes with 9-BBN dimers. Selective dehalogenation of tertiary alkyl, benzyl, and allyl halides in the presence of secondary or primary alkyl or aryl halides is possible with (165). The... 

Functionalized allyllithium compounds of type XIII are also homoenolate equivalents [122,130], but in their reaction with electrophiles sometimes it is not possible to control the regioselectivity. These compounds have been prepared mainly by either deprotonation or tin-lithium exchange. Deprotonation of (F)-cinnamyl-N,N-diisopropylcarbamate 155 with n-BuLi in the presence of (-[-sparteine in toluene gave a configurationally stable lithiated O-allyl carbamate (epi-156), which equilibrates at -50 °C to give the (R)-intermediate 156. Whereas the reaction of these compounds with Mel and MeOTs gave the /-attack, however acylation, silylation and stannylation took place at the a-position (Scheme 2.21) [131]. 

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