Alkynylstannanes formation

Two catalytic cycles are proposed to explain the difference in selectivity. In both cases, catalytic cycle is initiated by the oxidative addition of an alkynylstannane to nickel(O) species, leading to the formation of alkynylnickel(ll) complex 77 (Scheme 24).92 Then, an allene is inserted into the nickel(ll) complex in a manner which avoids steric repulsion with the butyl group to afford the anti-ir-a y complex 80. The carbometallation of the terminal alkyne can take place at the non-substituted allylic carbon of the corresponding syn-Ti-a y complex 78. The stereoselectivity is determined by the relative rate of the two possible insertion modes which depend on the ligand used. A bidentate... 

Admixture of alkynylstannanes, aldehydes, trimethylsilyl chloride, and InClj in acetonitrile at room temperature results in the formation of propargyl silyl ethers. In the synthesis of homoallylic alcohols, simple allylic halides can be used to form the tin halides in situ in water. ... 

As illustrated with the formation of 379, oxidative coupling between primary alkylzincs and alkynylstannanes occurs under similar conditions as those discussed above for the reaction between arylzincs and alkylindium reagents [165,166]. Desyl chloride is used as oxidant in the presence of Pd(dba)2 (2.5 mol%) at 60 °C in THF (Scheme 4.87) [273]. The same catalyst is also competent to promote the same coupling but starting from terminal alkynes. In this case, air can be used as oxidant and secondary alkylzincs are also suitable. The presence of CO is necessary to achieve good chemical yields (Scheme 4.87) [274]. 

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