Both 1-arylalk-3-en-1-ynes and alka-1,5-dien-3-ynes have been synthesized under extremely mild reaction conditions in good to high yields via a sequential Suzuki-type and Sonogashira reaction in a one-pot manner. Thus, the protocol involves Cu-mediated cross-coupling reaction of (E)-or (Z)-alkenyldisiamylborane with (trimethylsilyl)ethynyl bromide in the presence of 1 M NaOMe and Pd/Cu-catalyzed cross-coupling reaction with aryl or alkenyl iodide in the presence of aqueous n-Bu 4 NOH. The reaction with aryl iodide is tolerant of a wide variety of functional groups on the aromatic ring and leads to the stereoselective formation of (E)-and (Z)-1-arylalk-3-en-1-ynes. In addition, the reactions with (E)-and (Z)-1-iodoalk-1-enes have accomplished the construction of all possible combinations of geometrical isomers, (E,E)-, (Z,E)-, (E,Z)-, and (Z,Z)-alka-1,5-dien-3-ynes.
The cross-coupling reaction of (E)-and (Z)-alk-1-enyldialkylborane with (trimethylsilyl)ethynyl bromide proceeds in the presence of a catalytic amount of copper(II) acetylacetonate and a base under extremely mild conditions to provide conjugated enynes with a distal carbon-carbon triple bond. Employing sodium methoxide (1 M) as the base results in not only cross-coupling but also desilylation affording both (E)-and (Z)-alk-3-en-1-ynes, exclusively, while lithium hydroxide monohydrate gives both (E)-and (Z)-1-(trimethylsilyl)alk-3-en-1-ynes with high regio-and stereoselectivity. On the other hand, the cross-coupling reaction of (Z)-1-(trimethylsilyl)alk-1-enyldicyclohexylborane with (trimethylsilyl)ethynyl bromide proceeds in the presence of a small amount of copper(I) iodide and aqueous sodium hydroxide under extremely mild conditions to afford (Z)-1,3-bis(trimethylsilyl)alk-3-en-1-yne with high regio-and stereoselectivity. In addition, treatment of the resulting product with sodium methoxide (1 M) leads to the stereoselective formation of (Z)-3-(trimethylsilyl)alk-3-en-1-yne in a one-pot synthesis.
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