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Highly (≥98 %) Selective Trisubstituted Alkene Synthesis of Wide Applicability via Fluoride‐Promoted Pd‐Catalyzed Cross‐Coupling of Alkenylboranes
Author(s) -
Negishi Eiichi,
Tobrman Tomas,
Rao Honghua,
Xu Shiqing,
Lee ChingTien
Publication year - 2010
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.201000051
Subject(s) - chemistry , pinacol , propyne , alkene , alkyne , catalysis , medicinal chemistry , aryl , yield (engineering) , trimethylsilyl , organic chemistry , stereoselectivity , borane , alkyl , materials science , metallurgy
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 n Bu 4 NF(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 % stereoselectivity. 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.