Stannylcuprates substitution reactions

Like their carbon counterparts, silylcuprates and stannylcuprates readily participate in SN2 -substitution reaction with allylic electrophiles.43,51 For example, <37z//-diastereoselective allylic substitution of the vinyl oxiranes 147 with the lower-order cyanocuprate (PhMe2Si)Cu(CN)Li cleanly affords the allylsilanes 148 (Scheme 38).106 Products of this type can be converted into the corresponding diols with retention of configuration by Tamao-Fleming oxidation 53,53a,53b,107... 

The stannylcupration of alkynes has been widely studied. Reaction of alkynes with lithium bis(tributylstannyl) cuprate leads to r -2-(tri butyl stannyl) vinyl cuprates, which are synthetically equivalent to cis- 1,2-ethylene dianions. Addition of the tin-copper reagent across the triple bond occurs i>7/-stereospecifically, thus providing Z-vinylstannanes. Phenylacetylene reacts with the tin cuprate with a regiochemistry opposite to that of 1-decyne.294 The intermediate cuprates react well with the various electrophiles.295 For example, the reaction with ethylene oxide gives primary alcohols, and further treatment of their />-toluenesulfonates with butyllithium gives 1-substituted cyclobutenes (Equation (120)) 294... 

An interesting application of a stannylcuprate SN2 -substitution was reported by Echavarren and co-workers.111 Highly regioselective reaction at the sterically less hindered double bond of the bisallylacetate 154 with the mixed cuprate (Bu3nSn)(Bun)CuLi LiCN provided the allylstannane 155 with high yield, which was then submitted to a palladium-catalyzed carbocyclization reaction (Scheme 40). The product 156 was easily transformed into the natural product ( )-10- /-elemol 157. 

Stannylcuprates will also react with enol triflates (equation 8-21)41 and with vinyl iodides (equation 8-22)42 to give vinylstannanes, in a reaction which may be regarded either as a nucleophilic substitution or as stannylcupration followed by elimination of CuX. 

---