Alkenyltin compounds

In organic synthetic procedures, alkenyltin compounds are often prepared with a view to subsequent transmetalla-tion with lithium, or to the Stille coupling reaction with a palladium catalyst (Equations (70) and (71)). 

Tributyltin hydride adds across C=C 77 bonds by a free-radical mechanism. Addition of BusSnH across alkynes is one of the best ways of making alkenyltin compounds, which are useful reagents in organic synthesis. The mechanism is exactly the... 

The most common routes to alkenyltin compounds involve reaction between an alkenyl-metallic compound and a tin halide, or the hydrostannation of an alkyne (see Section 4.4). In recent years, the stannylmetallation of alkynes has become increasingly important. Direct hydrogenation of an alkynylstannane to a vinylstannane does not appear to be practicable, presumably because the catalyst is poisoned by the tin compound, but cis addition of dihydrogen can be achieved by hydrozirconation followed by hydrolysis,1 or in some cases, by cyclotitanation followed by hydrolysis2 (Section 8.2.2 below). 

See Reference 231 for numerous alkenyltin compounds. See Reference 160 for similar compounds. 

F-Alkenyltin compounds may be prepared by transmetallation using triorganyltin halides. Several ( )-alkenylstannyl alcohols have been prepared from intramolecular cross-coupling in the synthesis of zearalenone shown in Scheme 12. ... 

The a-substituted alkenylmetals used in Pd-catalyzed cross-coupling have been mainly those containing Mg, Zn, B, and Sn, as shown in Table 12 as well as Schemes 54-57. Of these, a-substituted alkenylmetals containing Mg and Zn can readily be prepared by direct oxidative metaUation of 2-halo-l-alkenes that are easily accessible by Markovnikov addition of HX to 1-alkynes (Scheme 54). a-Substituted alkenyltin compounds have been prepared and used in the construction of bicyclic diene systems via intramolecular Stille coupling, as shown in Scheme 55. ... 

Some trans-a,, along with cw-a,/3-substituted alkenyltin compounds have been prepared and used in intramolecular coupling reactions to synthesize cyclic compounds,as shown in Scheme 69. The reaction could be mediated by stoichiometric CuCl instead of catalytic Pd complexes,while the use of Cu(I) as a cocatalyst in Stille coupling has been demonstrated. 

Several rearrangement products, including 2,5-dihydro-1,2,5-oxoniastannaboratoles, have been identified during the methanolysis of / -(alkyn-l-ylborate)alkenyltin compounds. The sfiuctures of the products have indicated that protolysis of an Sn—C= bond occurs first, followed by an MeO-alkenyl exchange reaction." ... 

In the Stille coupling, Pd catalyzes the direct linkage between alkenyl halides and alkenyltin compounds ... 

The reaction of certain palladium-heteroatom complexes to alkenes and alkynes is a versatile tool for the synthesis of alkanes and alkene having heteroatoms attached. In particular, the various B-B, B-Si, and B-Sn compounds can be used for palladium-catalyzed borylation of alkenes and alkynes (Scheme 5-2). Borostannylation takes place at ambient temperature, whereas silylboration " only proceeds at a temperature above 80 °C due to the slow oxidative addition of a B-Si bond to a palladium(O) catalyst. Both reactions selectively provide cz j-products via addition of silicone or tin to the internal carbon and boron. The reactions are compatible with various functional groups for both terminal and internal alkynes. Cross-coupling reaction of boranes with organic halides selectively occurs at the terminal C-B bonds to provide regiodefined and stereodefined alkenylboron, alkenylsilicon, and alkenyltin compounds. 

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