A
light-driven
method
for
the
contra-thermodynamic
positional
isomerization
of
olefins
is
described.
In
this
work,
stepwise
PCET
activation
a
more
substituted
and
thermodynami-cally
stable
olefin
substrate
mediated
by
an
excited-state
oxi-dant
Brønsted
base
to
afford
allylic
radical
that
cap-tured
Cr(II)
co-catalyst
furnish
allylchromium(III)
intermediate.
situ
protodemetalation
allylchromium
complex
methanol
highly
regioselective
affords
isomerized
less
thermodynamically
alkene
product.
The
higher
oxidation
potential
isomer
renders
it
inert
further
oxidant,
enabling
accumulate
in
solution
over
course
reaction.
broad
range
isopropylidene
substrates
ac-commodated,
including
enol
ethers,
enamides,
styrenes,
1,3-dienes,
tetrasubstituted
alkyl
olefins.
Mechanistic
investiga-tions
step
are
also
presented.
Journal of the American Chemical Society,
Год журнала:
2024,
Номер
146(27), С. 18606 - 18615
Опубликована: Июнь 28, 2024
In
recent
years,
progress
has
been
made
in
the
development
of
catalytic
methods
that
allow
remote
functionalizations
based
on
alkene
isomerization.
contrast,
protocols
alkyne
isomerization
are
comparatively
rare.
Herein,
we
report
a
general
Pd-catalyzed
long-range
alkynyl
alcohols.
Starting
from
aryl-,
heteroaryl-,
or
alkyl-substituted
precursors,
optimized
system
provides
access
preferentially
to
thermodynamically
more
stable
α,β-unsaturated
aldehydes
and
is
compatible
with
potentially
sensitive
functional
groups.
We
showed
migration
both
π-components
carbon–carbon
triple
bond
can
be
sustained
over
several
methylene
units.
Computational
investigations
served
shed
light
key
elementary
steps
responsible
for
reactivity
selectivity.
These
include
an
unorthodox
phosphine-assisted
deprotonation
rather
than
conventional
β-hydride
elimination
final
tautomerization
event.
ACS Catalysis,
Год журнала:
2020,
Номер
10(15), С. 8736 - 8741
Опубликована: Июль 21, 2020
We
report
a
newly
developed,
palladium-catalyzed
dehydrosilylation
of
terminal
alkylsilanes
that
combines
with
chain-walking
hydrosilylation
to
create
one-pot
isomerization
internal
olefins
olefins.
This
catalytic
is
one
the
few
examples
thermal
functionalizations
unactivated
alkylsilanes.
The
reaction
involves
transmetalation
an
alkylsilane,
β-hydride
elimination,
release
olefin,
and
reoxidation
palladium
catalyst.
A
variety
linear
underwent
overall
in
good
yields
regioselectivities.
Particularly
noteworthy,
isomerizations
occurring
over
seven
carbon
units
proceeded
are
comparable
those
unit.
Vinylic
phenylsulfones
containing
a
β-hydroxyl
stereocenter
undergo
diastereoselective
isomerization
to
the
corresponding
allylic
isomer
upon
treatment
with
1,8-diazabicyclo(5.4.0)undec-7-ene
(DBU).
Diastereoselectivity
of
this
reaction
increases
increasing
size
group
attached
carbinol
carbon
(up
>20:1
d.r.
tert-butyl).
Isolated
yields
isomerized
1,2-hydroxy
phenylsulfone
products
were
comparable
among
different
vinylsulfones
tested
(59-66%).
The
major
competing
pathway
was
C-C
bond
cleavage
process,
proposed
occur
after
initial
event.
sense
diastereoselection
consistent
all
substrates
investigated,
in
favor
erythro-isomer
based
on
NMR
analysis.
Organic Letters,
Год журнала:
2022,
Номер
24(4), С. 1005 - 1010
Опубликована: Янв. 26, 2022
We
report
a
dehydroboration
process
that
can
be
coupled
with
chain-walking
hydroboration
to
create
one-pot,
contra-thermodynamic,
short-
or
long-range
isomerization
of
internal
olefins
terminal
olefins.
This
occurs
by
sequence
comprising
activation
nucleophile,
iodination,
and
base-promoted
elimination.
The
proceeds
at
room
temperature
without
the
need
for
fluoride
base,
substrate
scope
this
is
expanded
over
those
previous
isomerizations
we
have
reported
silanes.
Angewandte Chemie,
Год журнала:
2024,
Номер
137(1)
Опубликована: Сен. 17, 2024
Abstract
Allylic
sulfones
are
valuable
motifs
due
to
their
medicinal
and
biological
significance
versatile
chemical
reactivities.
While
direct
allylic
C−H
sulfonylation
represents
a
straightforward
desirable
approach,
these
methods
primarily
restricted
terminal
alkenes,
leaving
the
engagement
of
internal
counterparts
formidable
challenge.
Herein
we
report
photocatalytic
approach
that
accommodates
both
cyclic
acyclic
alkenes
with
diverse
substitution
patterns
electronic
properties.
Importantly,
obtained
can
be
readily
diversified
into
wide
range
products,
thus
enabling
formal
alkene
transposition
all‐carbon
quaternary
center
formation
through
sequential
functionalization.
A
light-driven
method
for
the
contra-thermodynamic
positional
isomerization
of
olefins
is
described.
In
this
work,
stepwise
PCET
activation
a
more
substituted
and
thermodynami-cally
stable
olefin
substrate
mediated
by
an
excited-state
oxi-dant
Brønsted
base
to
afford
allylic
radical
that
cap-tured
Cr(II)
co-catalyst
furnish
allylchromium(III)
intermediate.
situ
protodemetalation
allylchromium
complex
methanol
highly
regioselective
affords
isomerized
less
thermodynamically
alkene
product.
The
higher
oxidation
potential
isomer
renders
it
inert
further
oxidant,
enabling
accumulate
in
solution
over
course
reaction.
broad
range
isopropylidene
substrates
ac-commodated,
including
enol
ethers,
enamides,
styrenes,
1,3-dienes,
tetrasubstituted
alkyl
olefins.
Mechanistic
investiga-tions
step
are
also
presented.
The
positional
isomerization
of
C–C
double
bonds
is
a
powerful
strategy
for
the
interconversion
alkene
regioisomers.
However,
existing
methods
provide
access
to
thermodynamically
more
stable
isomers
from
less
starting
materials.
Here
we
report
discovery
dual
catalyst
system
that
promotes
contra-thermodynamic
under
photochemical
irradiation,
providing
terminal
directly
conjugated,
internal
utility
method
demonstrated
in
deconjugation
diverse
electron
rich/poor
alkenes
and
through
strategic
application
natural
product
synthesis.
Mechanistic
studies
are
consistent
with
regiospecific
bimolecular
homolytic
substitution
(SH2')
mechanism
proceeding
an
allyl-cobaloxime
intermediate.
Catalysts,
Год журнала:
2021,
Номер
11(12), С. 1483 - 1483
Опубликована: Дек. 3, 2021
The
metathesis
of
1-hexene
and
(E)-anethole
in
the
presence
Grubbs
2nd
generation
catalyst
was
monitored
by
situ
1H
NMR
spectroscopy
at
different
temperatures
(15
°C,
25
45
°C)
anethole
mol
fractions
(XAnethole
≈
0.17,
0.29,
0.5,
0.71,
0.83).
Time
traces
confirmed
instantaneous
formation
(E)-1-(4-methoxyphenyl)-1-hexene,
cross-metathesis
product.
A
maximum
concentration
(E)-1-(4-methoxyphenyl)-1-hexene
is
reached
fairly
fast
(the
time
depending
on
reaction
conditions),
this
followed
a
decrease
due
to
secondary
metathesis.
more
dependent
XAnethole
than
temperature.
highest
TOF
(3.46
min−1)
obtained
for
where
0.16
°C.
product
however
achieved
after
6
min
with
an
fraction
0.84
preliminary
kinetic
study
indicated
that
first
order
kinetics.
Angewandte Chemie,
Год журнала:
2021,
Номер
133(16), С. 9079 - 9084
Опубликована: Янв. 28, 2021
Abstract
A
new
transformation
pattern
for
enantioselective
intramolecular
hydroacylation
has
been
developed
involving
an
alkene
isomerization
strategy.
Proceeding
through
a
five‐membered
rhodacycle
intermediate,
3‐enals
were
converted
to
C
3
‐
or
,C
5
‐chirogenic
cyclopentanones
with
satisfactory
yields,
diastereoselectivities,
and
enantioselectivities.
catalytic
cycle
theoretically
calculated
the
origin
of
stereoselection
is
rationally
explained.
A
light-driven
method
for
the
contra-thermodynamic
positional
isomerization
of
olefins
is
described.
In
this
work,
stepwise
PCET
activation
a
more
substituted
and
thermodynami-cally
stable
olefin
substrate
mediated
by
an
excited-state
oxi-dant
Brønsted
base
to
afford
allylic
radical
that
cap-tured
Cr(II)
co-catalyst
furnish
allylchromium(III)
intermediate.
situ
protodemetalation
allylchromium
complex
methanol
highly
regioselective
affords
isomerized
less
thermodynamically
alkene
product.
The
higher
oxidation
potential
isomer
renders
it
inert
further
oxidant,
enabling
accumulate
in
solution
over
course
reaction.
broad
range
isopropylidene
substrates
ac-commodated,
including
enol
ethers,
enamides,
styrenes,
1,3-dienes,
tetrasubstituted
alkyl
olefins.
Mechanistic
investiga-tions
step
are
also
presented.
