Hydrostannylation, of alkynes

Vinyl cuprates.17 Vinyl cuprates can be prepared conveniently by in situ trans-metallation of vinylstannanes, available by hydrostannylation of alkynes, with a cuprate such as (CH3)2Cu(CN)Li2 (equation I). Reagents prepared in this way effect conjugate addition of the vinyl group to an enone with essentially no transfer of the methyl group. 

The palladium-catalyzed coupling of aryl iodides with vinylstannanes (Stille coupling) leads to the formation of styrenes. With resin-bound vinylstannanes, this reaction can be conducted in such a way that simultaneous detachment from the support of the newly formed styrenes occurs. This has been realized intramolecularly in the preparation of macrocyclic lactones (Entry 4, Table 3.43). The required resin-bound vinylstannanes were prepared either by hydrostannylation of alkynes with a resin-... 

Figure 5.6.1 Cascade products from in situ hydrostannylation of alkynes...

Addition and cycloaddition. In the (dba)3Pd2-catalyzed hydrostannylation of alkynes the legiochemistry is controlled by the phosphine ligands. ( )-l-Tributylstannylalkenes are produced preponderantly in the presence of CysP or t-Bu3P, but much more 2-stannyl-l-aUcenes are obtained with PhsP. ... 

Scheme 2. EtjB-induced hydrostannylation of alkynes and its applications...

Et3B as a simple radical initiator was first discovered in hydrostannylation of alkynes [5], The reactions were performed at room temperature or below in the presence of a trace amount of oxygen (Scheme 2). Hydrostannylation was applied to the synthesis of dehydroiridodiol (1) and a-methylene-y-butyrolactone (2). Et3B-induced radical addition reactions of triphenylgermane [7], tris(trimethylsilyl)silane... 

The orientation and steric course of the hydrostannylation of alkynes to yield alkenylstannanes is determined by the nature of the reagent and the catalyst used. The trimethylstannylcopper reagent Me3SnCu Me2S adds regioselectively to terminal acetylenes 293 (n = 1,2,3,4 or 6, X = OH, Cl, OSiMe2Bu or 2-tetrahydropyranyl) to give, after treatment with methanol, the stannanes 294. ... 

Hydrostannylation of alkynes is less selective and mixtures of regio- and stereoisomers often result. The reaction is substrate dependent and, although mixtures of product alkenyl stannanes are normally formed, appropriate choice of the... 

Hydrostannylations. Hydrostannanes add to alkynes in uncatalyzed reactions at 60 °C. Phenylacetylene, for instance gives a mixture of ( )- and (Z)-vinylstannanes, wherein the tin atom has added to the terminal carbons. In the presence of Wilkinson s catalyst, however, the hydrostannylation proceeds at 0 °C to give mostly the regioisomeric vinylstannanes (eq 23). Terminal stannanes in the latter process seem to result from competing free radical additions. This may not be a complication with some other catalysts the complexes PdCl2(PPh3)2 and Mo( j -allyl) (CO)2(NCMe)2 also mediate hydrostannylations of alkynes, and they are reported to be 100% cis selective. Hydrostannanes and thiols react in a similar way to silanes and alcohols (eq 24). ... 

Tributyltin Hydride. This reagent can be used for reduction of halides, hydrostannylation of alkynes, and preparation of hexabutylditin. 

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