Stereoselective synthesis of terminal conjugated enynes using alkenylboron compounds

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We have studied the copper(II) acetylacetonate-catalyzed cross-coupling reaction of (E)- and (Z)-1-alkenyldialkylborane with 2-bromo-1-(trimethylsilyl)acetylene and the application of the cross-coupled products, (E)- and (Z)-3-alken-1-yne, to Sonogashira reaction. The results are as follows:1. By using NaOMe (1M solution in methanol) as a base, the cross-coupling reaction as well as protodesilation proceeded simultaneously under very mild conditions, at -15 ℃ to room temperature, to provide (E)- and (Z)-3-alken-1-ynes in good yields with high regio- and stereoselectivities.2. By using LiOH・H_2O as a base, the cross-coupling reaction proceeded with practically no protodesilation under the same conditions to afford (E)- and (Z)-l-trimethylsilyl-3-alken-1-ynes in moderate to good yields with high regio- and stereoselectivities.3. Both (E)- and (Z)-3-alken-1-yne, in situ generated by the copper(II) acetylacetonate-catalyzed cross-coupling reaction, were subjected to the reaction with aryl iodide in a one-pot manner, and hence the reaction proceeded at room temperature in the presence of PdCl_2(PPh_3)_4-CuI as catalyst and tetrabutylammonium hydroxide as base to give the corresponding arylated conjugated enynes in high yields with high regio- and stereoselectivities.