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

( 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.