Stannylcupration of alkynes

Scheme 3.23. Cyclobutene and alkylidine cyclobutane synthesis by stannylcupration of alkynes and trapping of the resultant vinylcuprate with epoxides [15c],...

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... 

The syn stereoselectivity exhibited the stannylcupration of alkynes is used for the synthesis of stannylated enynes 139 which could be readily transformed to the desired enediynes [67] [Eq. (46)]. 

Scheme 3.21. Regioselectivity in the stannylcupration of l-alkynes, -hydroxy-l-alkynes, enynes, and propargyl alcohols.

Regioselective stannylcupration of terminal alkynes and allenes, followed by quenching of the cuprate intermediate with ethylene oxide, provides a facile synthesis of cyclobutene and alkylidine cyclobutane derivatives, respectively (Scheme 3.23) [15c]. A number of total syntheses have exploited regioselective stannylcup-... 

Regio- and stereoselective stannylcupration of terminal alkynes provides the corresponding (R)-l-stannylalkenes, exclusively [62,150,153-167]. Methylation of the intermediary alkenylcopper species provides the corresponding trisubsti-tuted alkenyltin reagent, stereoselectively [168]. Carbostannylation of alkynes offers another sophisticated possibility [32,169-179]. Hetero-atom assisted lithi-ation and subsequent stannylation of alkene also provides the corresponding alkenyltins (Scheme 36) [180]. 

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