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. 2010 Dec 1;50(5-6):696-701.
doi: 10.1002/ijch.201000051.

Highly(≥98%) Selective Trisubstituted Alkene Synthesis of Wide Applicability via Fluoride-Promoted Pd-Catalyzed Cross-Coupling of Alkenylboranes

Ei-Ichi Negishi  1 , Tomas Tobrman, Honghua Rao, Shiqing Xu, Ching-Tien Lee
Affiliations

Highly(≥98%) Selective Trisubstituted Alkene Synthesis of Wide Applicability via Fluoride-Promoted Pd-Catalyzed Cross-Coupling of Alkenylboranes

Ei-Ichi Negishi et al. Isr J Chem. .

Abstract

(Z)-β-bromo-1-propenyl(pinacol)borane(4), recently made available in 85% yield as a ≥98% isomerically pure compound via bromoboration of 1-propyne, has been converted to β-alkyl-, aryl-, and alkenyl-substituted (Z)-2-methyl-1-alkenyl(pinacol)boranes(2a) in ca. 75% yield based on propyne via Pd-catalyzed Negishi alkenylation with suitable organozinc bromide. The previously sluggish and modest-yielding Suzuki alkenylation of β,β-disubstituted alkenylboranes has been significantly promoted by fluorides, especially nBu4NF(TBAF) or CsF to give trisubstituted alkenes, i.e., (Z)-β-Me-substituted 3-i-3-xi and (E)-β-Ph-substituted 2b-i and 2b-ii. In all cases, each alkene product was formed in a ≥98% seteoselectivity. The propyne-based protocol nicely complements the widely used Zr-catalyzed alkyne methylalumination-Pd-catalyzed alkenylation by providing a highly stereoselective(≥98%) route to (Z)-Me-substituted alkenes.

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Figures

Figure 1
Figure 1. The structure of PEPPSI™-IPr(8)
Scheme 1
Scheme 1
Scheme 2
Scheme 2
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Scheme 6
See this image and copyright information in PMC

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