Desymmetrization of diyne

The pure E stereochemistry of the vinylsilane 21 clearly shows that the carbocylization proceeds in a totally stereoselective fashion to give, under these conditions (20 °C, 5 min) the configurationally stable (Z)-alkenylzinc bromide [21] 20 via a syn addition of the allenic zinc bromide to the acetylenic moiety. This carbocyclization represents a new desymmetrization of diynes such as 18 which serves to deliver functionalized exo-... 

Iska VBR, Verdolino V, Wiest O, Helquist P. Mild and efficient desymmetrization of diynes via hydroamination application to the synthesis of ( )-monomorine 1. J. Org. Chem. 2010,75(4) 1325-1328. 

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