Over the past 40 years, intramolecular hydroacylation has favored five-membered rings, in preference to four membered rings. Herein, we report a catalyst derived from earth-abundant cobalt that enables preparation of cyclobutanones, with excellent regio-, diastereo-, and enantiocontrol, under mild conditions (2 mol % catalyst loading and as low as 50 °C).
Phosphonate-directed
ortho C–H borylation of aromatic phosphonates
is reported. Using simple starting materials and commercially accessible
catalysts, this method provides steady access to o-phosphonate arylboronic esters bearing pendant functionality and
flexible substitution patterns. These products serve as flexible precursors
for a variety of highly substituted phosphoarenes, and in situ downstream
functionalization of the products is described.
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 preparation of tertiary nitroalkanes via the nickel-catalyzed alkylation of secondary nitroalkanes using aliphatic iodides is reported. Previously, catalytic access to this important class of nitroalkanes via alkylation has not been possible due to the inability of catalysts to overcome the steric demands of the products. However, we have now found that the use of a nickel catalyst in combination with a photoredox catalyst and light leads to much more active alkylation catalysts. These can now access tertiary nitroalkanes. The conditions are scalable as well as air and moisture tolerant. Importantly, reduction of the tertiary nitroalkane products allows rapid access to α-tertiary amines.
High-throughput
experimentation (HTE) workflows are efficient means
of surveying a broad array of chiral catalysts in the development
of catalytic asymmetric reactions. However, the use of traditional
high-pressure liquid chromatography (HPLC)-UV/vis methodology to determine
enantiomeric excess (ee) from the resulting reactions is often hampered
by coelution of other reaction components, resulting in erroneous
ee determination when crude samples are used and ultimately requiring
product isolation prior to ee analysis. In this study, using four
published reactions selected as model systems, we demonstrate that
the use of liquid chromatography–mass spectrometry (LC–MS),
supercritical fluid chromatography–mass spectrometry (SFC-MS),
and selected ion monitoring (SIM) mass chromatography provides a highly
accurate means to determine the ee of products in crude reaction samples
using commonplace, low-cost MS detectors. Using ion selection, coeluting
signals can be deconvoluted to provide accurate integrations of the
target analytes. We also show that this method is effective for samples
lacking UV/vis chromophores, making it ideal for HTE workflows in
asymmetric catalysis.
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