Hydroboration of Enynes and Diynes

With the availability of wide variety of hydroborating agents, it is now possible to hydroborate either of the internal or the terminal unsaturation. In a mixture of an alkene and an alkyne, 9-BBN preferentially attacks the carbon-carbon double bond only (Chart 5.26) [1]. 

Similarly 9-BBN differentiates between the internal and the terminal triple bonds (Eq. 5.41) of diynes, hydroborating only the terminal carbon-carbon triple bond. 

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