Stannyl groups

The ( )-vinylsilane 151 was prepared by treatment of the silylstannation product 150 with hydrogen iodide[75] and the silylzincation product with water[70]. The silylstannylation of 1-ethoxyacetylene proceeds at room temperature using Pd(OAc)i and 1,1,3,3-tetramethylbutyl isocyanide regioselec-tively and an Si group is introduced at the ethoxy-bearing carbon. Subsequent Cul- and Pd-catalyzed displacement of the stannyl group in the product 152 with allyl halide, followed by hvdrolvsis, affords the acylsilane 153[79],... 

Sulfonation of the aromatic ring of l, 2, 2 -trifluorostyrene below 0 C does not give satisfactory yields with chlorosulfonic acid or a sulfur trioxide-dioxane complex Tar forms on heating In contrast, under similar conditions ipso substitution IS facile at the position of a trialkylsilyl or -stannyl group Thus, 4-trimethyl-silyl-T 2, 2 D-trifluorostyrene affords the corresponding trimethylsilyl sulfonate [20] (equation 9)... 

Alkenyl silanes and stannanes have the potential for nucleophilic delivery of vinyl groups to a variety of electrophiles. Demetallation also occurs in these reactions, so the net effect is substitution for the silyl or the stannyl group. 

With terminal alkynes, the stannyl group is added at the unsubstituted carbon and the Z-stereoisomer is initially formed but is readily isomerized to the E-isomer.140... 

Enantioselective Addition Reactions of Allylic Stannanes. There have been several studies of the enantiomers of a-oxygenated alkenyl stannanes. The chirality of the a-carbon exerts powerful control on enantioselectivity with the preference for the stannyl group to be anti to the forming bond. This is presumably related to the stereoelectronic effect that facilitates the transfer of electron density from the tin to the forming double bond.182... 

Polar functional groups such as carbonyl, cyano, and sulfoxide, as well as silyl and stannyl groups, exert a strong directing effect, favoring proton removal from the geminal methyl group.171... 

In contrast to a, (o-diepoxyorganostannanes, trialkylstannyls are not readily polymerized. When stored in the free air, they are gradually converted to a powder which may be explained by opening of the oxirane ring upon the catalytic action of alkyl(aryl)stannyl groups. 

Alkoxytrialkylstannanes react with alkynylcyclobutenones (101) to yield stannylated quinones285. The stannyl group can be displaced by aryl or hetaryl groups, as shown in reaction 32286a. 

The Z- or -configuration of the vinyl groups of linchpins (106,107) is preserved when the stannyl groups are displaced by triflate esters, as shown in reactions 49 and 50301. 

Stannyl groups attached to quinones can be displaced by aryl, heteryl and other groups, as shown in reactions 32286 and 67314. 

Reaction of the stannylborane 9 with an allenyne gives a cyclization product, in which the boryl and stannyl groups are introduced to the acetylenic terminus and the allenic central carbon, respectively (Equation (104)).159 Based on the assumption that an unsaturated functionality initially inserts into the Pd-B bond of (boryl)(stannyl)palladium(n) species, it seems likely that the alkyne moiety is more reactive than the allene moiety in this reaction. 

The heteroarylstannanes bear the same relation to the arylstannanes as do the heteroarenes to the arenes, with the extra factor that the Lewis acidity of the stannyl group may cause the heteroarylstannanes to have self-associated structures. 

Cyclopentadiene is acidic enough to react with aminostannanes, and at 80 °C, four stannyl groups can be introduced into the ring (Equation (116)).305... 

Ferroceneophanes (ansa-ferrocenes) have been prepared where the cyclopentadienyl rings are bridged through one, two, or three stannyl groups. 

While most of the examples studied employed a stannyl group as the group 14 metal, the use of an a-silyl ether was also examined. In this case, the same cyclic product was formed as in the corresponding a-stannyl ether substrate. However, the yield of product obtained was higher when the tin based starting material was employed (83% vs 66%). 

It was anticipated that a C4 -trialkyIstannyl group would intercept the C4 radical and result in loss of antimalarial activity. Indeed, 31 and 32 were inactive and iron(II) degradation afforded two major products in which the stannyl group had been eliminated (Scheme 6). They proposed that the deoxo derivative 33 was produced by elimination of a... 

Because silyl and stannyl groups are good a-electron donors, their attachment at the y carbon of 4 should be stabihzing and thus accelerate the rate of formation of 4. In agreement with this conjecture, our calculations predicted that stabilization of 4... 

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