ACS Catalysis,
Год журнала:
2024,
Номер
14(9), С. 7149 - 7156
Опубликована: Апрель 23, 2024
A
cooperative
NHC/nickel
catalytic
methodology
has
been
developed
for
the
synthesis
of
ketones
employing
aromatic
aldehydes
and
tertiary
alkyl
iodides.
All
key
steps
postulated
cycle
were
validated
with
comprehensive
stoichiometric
electrochemical
studies,
including
reduction
NiII
by
deprotonated
Breslow
intermediate,
Ni0
promoted
halogen-atom
abstraction
to
generate
transient
radicals,
coupling
between
latter
persistent
acyl
thiazolium
radical
intermediate.
Such
a
broadly
proposed
accepted,
yet
elusive,
intermediate
isolated
studied
single-crystal
X-ray
diffraction
study.
Angewandte Chemie International Edition,
Год журнала:
2023,
Номер
62(31)
Опубликована: Июнь 1, 2023
The
cross-electrophile
coupling
(XEC)
represents
a
powerful
strategy
for
C-C
bond
formation.
However,
controlling
the
enantioselectivity
in
these
processes
remains
challenge.
Here,
we
report
an
unprecedented
enantioselective
XEC
of
α-amino
acid
derivatives
with
aryl
bromides,
enabled
by
alcohols
as
reducing
agents
via
Ni/photoredox
catalysis.
This
mechanistically
distinct
approach
exploits
ability
photocatalytically
generated
α-hydroxyalkyl
radicals
to
convert
alkyl
electrophiles
corresponding
that
are
then
enantioselectively
coupled
bromides.
readily
scalable
protocol
allows
modular
access
valuable
enantioenriched
benzylic
amines
from
abundant
and
inexpensive
precursors,
is
applicable
late-stage
diversification
broad
functional
group
tolerance.
Mechanistic
studies
rationalize
versatility
this
alcohol-based
reactivity
radical
generation
subsequent
asymmetric
cross-coupling.
We
expect
cross-coupling
will
render
general
platform
development
appealing
yet
challenging
XECs.
ACS Catalysis,
Год журнала:
2023,
Номер
13(17), С. 11277 - 11290
Опубликована: Авг. 11, 2023
Reactions
that
cleave
C–C
bonds
and
enable
functionalization
at
both
carbon
sites
are
powerful
strategic
tools
in
synthetic
chemistry.
Stereodefined
cyclopropyl
ketones
have
become
readily
available
would
be
an
ideal
source
of
3-carbon
fragments,
but
general
approaches
to
net
activation/difunctionalization
unknown.
Herein,
we
demonstrate
the
cross-coupling
with
organozinc
reagents
chlorotrimethylsilane
form
1,3-difunctionalized,
ring-opened
products.
A
combination
experimental
theoretical
studies
rules
out
more
established
mechanisms
sheds
light
on
how
cooperation
between
redox-active
terpyridine
(tpy)
ligand
nickel
atom
enables
bond
activation
step.
The
reduced
(tpy·–)NiI
species
activates
via
a
concerted
asynchronous
ring-opening
transition
state.
resulting
alkylnickel(II)
intermediate
can
then
engaged
by
aryl,
alkenyl,
alkylzinc
furnish
cross-coupled
This
allows
quick
access
products
difficult
make
conjugate
addition
methods,
such
as
β-allylated
β
-benzylated
enol
ethers.
utility
this
approach
is
demonstrated
synthesis
key
(±)-taiwaniaquinol
B
total
prostaglandin
D1.
Chemical Science,
Год журнала:
2024,
Номер
15(16), С. 5814 - 5831
Опубликована: Янв. 1, 2024
Sacrificial
anodes
enable
reductive
electrosynthesis
but
can
inadvertently
limit
the
conditions
compatible
with
organic
reactions.
Addressing
challenges
that
arise
at
sacrificial
improve
yields
and
streamline
reaction
optimization.
Zinc
and
manganese
are
widely
used
as
reductants
in
synthetic
methods,
such
nickel-catalyzed
cross-electrophile
coupling
(XEC)
reactions,
but
their
redox
potentials
unknown
organic
solvents.
Here,
we
show
how
open-circuit
potential
measurements
may
be
to
determine
the
thermodynamic
of
Zn
Mn
different
solvents
presence
common
reaction
additives.
The
impact
these
is
analyzed
for
a
pair
Ni-catalyzed
each
showing
preference
one
two
reductants.
N-alkyl-2,4,6-triphenylpyridinium
reagents
(Katritzky
salts)
with
aryl
halides
then
compared
under
chemical
conditions,
using
or
reductants,
electrochemical
performed
at
applied
corresponding
reduction
optimized
achieve
maximum
yield.
collective
results
illuminate
important
role
reductant
XEC
reactions.
Abstract
Herein,
the
use
of
economically
and
environmentally
friendly
bis(pinacolato)diboron
(B
2
Pin
)
is
described
as
a
non‐metallic
reductant
in
mediating
Ni‐catalyzed
C(sp
3
)–C(sp
reductive
cross‐coupling
alkyl
electrophiles
with
aryl/vinyl
halides.
This
method
exhibits
excellent
suitability
for
heteroaryl
halides
halides/Katritzky
salts.
The
present
study
compatible
an
situ
halogenation
alcohol
method,
allowing
selective
mono‐functionalization
diols
bio‐relevant
alcohols
(e.g.,
carbohydrates).
B
shows
potential
easy
scalability
without
introducing
additional
metal
impurities
into
products.
It
observed
first
time
realm
cross‐electrophile
coupling
chemistry
that
can
sever
to
reduce
Ni
II
0
.
mechanistic
insight
may
inspire
development
new
bond‐forming
methodologies
otherwise
be
difficult
achieve
reductant.
Organic Letters,
Год журнала:
2024,
Номер
26(31), С. 6556 - 6561
Опубликована: Июль 31, 2024
Cross-electrophile
coupling
reactions
that
forge
C(sp3)–C(sp3)
bonds
are
strategic
methods
for
the
synthesis
of
molecules
with
high
F(sp3),
yet
very
few
employ
electrochemical
conditions
as
necessary
reductant.
Herein,
we
report
an
intramolecular
cross-electrophile
reaction
1,3-diol
derivatives
to
access
aliphatic
and
aryl
cyclopropanes,
including
spirocyclic
fused
bicyclic
cyclopropanes.
The
scalable
(eXEC)
employs
a
nonsacrificial
anode
in
undivided
cell.
The
study
addresses
triaminoalkenes
derived
from
[3]ferrocenophane‐type
cyclic
(alkyl)(amino)carbenes
(fcCAACs)
fc(CPh
2
CNR)
(fc
=
1,1′‐ferrocenylene)
and
N
‐heterocyclic
carbenes
(NHCs).
Stable
target
compounds
are
obtained
in
good
yields
as
crystalline
solids
by
the
combination
of
[fc(CPh
CHNMe)][BF
4
]
with
,
′‐dimethylimidazolin‐2‐ylidene
CHN‐
p
‐C
6
H
‐
t
Bu)](OTf)
1,3,4,5‐tetramethylimidazolin‐2‐ylidene,
respectively,
followed
treatment
resulting
addition
product
KN(SiMe
3
)
.
Due
to
presence
a
triaminoethene
unit
ferrocene
moiety,
four
redox
states
expected
for
such
fcCAAC–NHC
heterodimers,
viz.,
electroneutral,
mono‐,
di‐,
tricationic.
An
investigation
their
behavior
electrochemical
methods
(cyclic
voltammetry
differential
pulse
voltammetry)
has
revealed
that
these
undergo
two
consecutive
one‐electron
oxidations,
poor
stability
dicationic
species
solution
preventing
an
observation
tricationic
state.
A
density
functional
theory
(DFT)
shows
highest
occupied
molecular
orbital
(HOMO)
is
localized
on
C
CN
atom,
which,
agreement
electron
paramagnetic
resonance
results,
site
first
oxidation.
second
oxidation
mainly
involves
Fe
where
HOMO−1
localized,
triplet
ground
state
composed,
approximation,
carbon‐centered
iron‐centered
radical.
