Arylethyne Bromoboration-Negishi Coupling Route toE- orZ-Aryl-Substituted Trisubstituted Alkenes of ≥98% IsomericPurity. New Horizon in the Highly Selective Synthesis of Trisubstituted Alkenes.
The hitherto unprecedented palladium-catalyzed cross-coupling of (Z)-β-bromo-β-arylethenylboranes can be made to proceed satisfactorily through (1) the use of highly catalytically active bis(tri-tert-butylphosphine)palladium or dichloro[N,N-bis-(2,6-diisopropylphenyl)imidazol-2-yl](m-chloropyridine)palladium and (2) conversion of dibromoboryl group to (pinacol)boryl group. Thus, a wide variety of carbon groups can be used to substitute bromine in ≥98% stereo- and regioselectivity, while suppressing the otherwise dominant β-debromoboration. Together with the alkylethyne-based protocols, the alkyne bromoboration-Negishi coupling tandem process has emerged as the most widely applicable and highly selective route to trisubstituted alkenes including those that are otherwise difficult to access.
Herbert C. Brown Laboratories of Chemistry, Purdue University, 560 Oval Dr., West Lafayette, IN 47907-2084, USA.
Chao
C
Wang
Zhaoqing
Z
Xu
Tomas
T
Tobrman
Ei-Ichi
EI
Negishi
(Z)-β-bromo-β-arylethenylboranes; Negishi coupling; arylethyne bromoboration; bis(tri-tert-butylphosphine)palladium; dichloro[N,N-bis-(2,6-diisopropylphenyl)imidazol-2-yl](m-chloropyridine)palladium