Stannylcupration alkynes

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-... 

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

Alkyn-l-ols, silver-catalyzed cycloisomerizations, 9, 561 Alkynones, stannylcupration, 9, 374... 

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... 

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]. 

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)]. 

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