An extremely efficient cobalt catalyst for the hydroboration of both vinylarenes and aliphatic α-olefins with pinacolborane is described, providing the anti-Markovnikov products with excellent regio- and chemoselectivity, broad functional-group tolerance, and high turnover numbers (up to 19,800). The alkene hydroboration route is further extended to a two-step, one-pot hydroboration and cross-coupling of alkylboronates with aryl chlorides.
We report the synthesis of cobalt complexes of novel iminopyridine-oxazoline (IPO) ligands and their application to the asymmetric hydroboration of 1,1-disubstituted aryl alkenes. The new catalysts afforded α-alkyl-β-pinacolatoboranes with exclusive regioselectivity in high yields with up to 99.5% ee. Furthermore, we have applied this method to an efficient synthesis of naproxen.
A series of iron complexes of chiral iminopyridine-oxazoline (IPO) ligands have been synthesized. The most sterically hindered iron catalyst exhibits excellent activity (up to 99% yield) and high enantioselectivity (up to 93% ee) in asymmetric hydrosilylation of aryl ketones.
We
disclose the synthesis of a series of manganese complexes of
chiral iminopyridine oxazoline ligands and their application in the
first manganese-catalyzed asymmetric ketone hydrosilylations. The
most sterically hindered manganese catalyst bearing two CH(Ph)
2
groups at the 2,6-ortho positions of the imino aryl ring
and a
t
Bu group on the oxazoline ring furnishes the
secondary alcohols in high enantioselectivities and yields.
We
report an asymmetric homocoupling of ortho-(iodo)arylphosphine
oxides and ortho-(iodo)arylphosphonates
resulting in highly enantioenriched axially chiral bisphosphine
oxides and bisphosphonates. These products are readily converted to
enantioenriched biaryl bisphosphines without need for chiral
auxiliaries or optical resolution. This provides a practical route
for the development of previously uninvestigated atroposelective
biaryl bisphosphine ligands. The conditions have also proven effective
for asymmetric dimerization of other, non-phosphorus-containing aryl
halides.
The asymmetric hydrogenation
of vinylsilanes catalyzed by a new C
1-symmetric
phosphine–pyridine–oxazoline
cobalt complex is described. The method provides an efficient approach
to chiral tertiary silanes with enantioselectivities up to 99% ee.
Furthermore, the o-methyl-substituted benzylic silane
products undergo ruthenium-catalyzed dehydrogenative silylation to
produce chiral benzosilolanes in high yields without racemization
of the stereogenic center α to the quaternary Si atom.
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