Highly Regio- and Stereoselective Synthesis of (Z)-Trisubstituted Alkenes via Propyne Bromoboration and Tandem Pd-Catalyzed Cross-Coupling
Chao Wang, Tomas Tobrman, Zhaoqing Xu and Ei-ichi Negishi*
*Herbert C. Brown Laboratories of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, Email: negishipurdue.edu
C. Wang, T. Tobrman, Z. Xu, E.-i. Negishi, Org. Lett., 2009, 11, 4092-4095.
DOI: 10.1021/ol901566e (free Supporting Information)
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Bromoboration of propyne with BBr3 proceeds in syn-selectivity to produce (Z)-2-bromo-1-propenyldibromoborane, which is prone to stereoisomerization. Treatment with pinacol yields the stable and storable pinacolboronate. Negishi coupling gives trisubstituted (Z)-alkenylpinacolboronates in good yields. Iodinolysis of the boronates affords alkenyl iodides in good yields.
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