Copper‐Catalyzed Three‐Component Borylstannylation of Alkynes

Regio‐ and stereoselective installation of boryl and stannyl moieties into a carbon–carbon triple bond of various alkynes has been achieved based on a three‐component coupling reaction by using a diboron and a tin alkoxide with the aid of a copper(II) acetate–tricyclohexylphosphine complex, giving diverse vic‐borylstannylalkenes in a straightforward manner. Carbon–tin and carbon–boron bonds of the resulting borylstannylation product are successively transformed into carbon–carbon bonds by a Migita–Kosugi–Stille and a Suzuki–Miyaura coupling, leading to the formation of (Z)‐tamoxifen with anti‐breast cancer activity.