ja5b02052_si_001.pdf (9.76 MB)
para-C–H Borylation of Benzene Derivatives by a Bulky Iridium Catalyst
journal contribution
posted on 2015-04-22, 00:00 authored by Yutaro Saito, Yasutomo Segawa, Kenichiro ItamiA highly para-selective
aromatic C–H borylation has been accomplished.
By a new iridium catalyst bearing a bulky diphosphine ligand, Xyl-MeO-BIPHEP,
the C–H borylation of monosubstituted benzenes can be affected
with para-selectivity up to 91%. This catalytic system
is quite different from the usual iridium catalysts that cannot distinguish meta- and para-C–H bonds of monosubstituted
benzene derivatives, resulting in the preferred formation of meta-products. The para-selectivity increases
with increasing bulkiness of the substituent on the arene, indicating
that the regioselectivity of the present reaction is primarily controlled
by steric repulsion between substrate and catalyst. Caramiphen, an
anticholinergic drug used in the treatment of Parkinson’s disease,
was converted into five derivatives via our para-selective
borylation. The present [Ir(cod)OH]2/Xyl-MeO-BIPHEP catalyst
represents a unique, sterically controlled, para-selective,
aromatic C–H borylation system that should find use in streamlined,
predictable chemical synthesis and in the rapid discovery and optimization
of pharmaceuticals and materials.