Highly Stereo- and Regioselective Synthesis of (Z)-Trisubstituted Alkenes via 1-Bromo-1-alkyne Hydroboration−Migratory Insertion−Zn-Promoted Iodinolysis and Pd-Catalyzed Organozinc Cross-Coupling
- 7 November 2007
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 129 (47) , 14788-14792
- https://doi.org/10.1021/ja0772039
Abstract
Hydroboration of 1-bromo-1-alkynes with dibromoborane followed by addition of 3 or 4 equiv of Me2Zn provides an efficient and selective route to (Z)-2-alkenyldimethylboranes (3) or (Z)-2-alkenylmethylzincs (4), respectively, which have been successfully applied to one-pot Suzuki (B - I) or Negishi (Zn - I) coupling in some less demanding cases. However, in more demanding cross-coupling reactions, only the use of either (Z)-2-alkenyliodides (5) or the alkenylzincs prepared from lithiation and then zincation of 5 proves to be highly satisfactory (Zn - II or Zn - III protocol). On the contrary, the corresponding organoboron coupling under B - II or B - III protocol appears to be less satisfactory. Preliminary studies indicate that certain substituents proximal to trisubstituted alkenes seriously affect the course of the desired alkenylboron cross-coupling.Keywords
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