General Chemoselective Suzuki–Miyaura Coupling of Polyhalogenated Aryl Triflates Enabled by an Alkyl-Heteroaryl-Based Phosphine Ligand

This study
describes a general chemoselective Suzuki–Miyaura coupling
of polyhalogenated aryl triflates with the reactivity order of C–Cl
> C–OTf using a Pd/L33 catalyst. The methine
hydrogen
and the steric hindrance offered by the alkyl bottom ring of L33 were found to be key factors in reactivity and chemoselectivity.
With the Pd/L33 catalyst, a wide range of polyhalogenated
(hetero)­aryl triflates, which were independent of the substrates and
of the relative positioning of the competing reaction sites, coupled
well with (hetero)­aryl, alkenyl, and alkylboronic acids to obtain
the corresponding products with good chemoselectivity and yields.
The chemoselective reaction could easily be scaled up to the gram
scale, and the use of parts per million levels of Pd catalyst (as
low as 10 ppm Pd) was achieved.