Organometallics,
Год журнала:
2020,
Номер
39(17), С. 3232 - 3239
Опубликована: Авг. 31, 2020
The
titanocene
imido
complex
2
with
a
m-terphenyl
moiety
is
synthesized
by
reacting
Cp2Ti(η2-Me3SiC2SiMe3)
(1)
azide.
Subsequent
reactivity
studies
tetrahydrofuran,
pyridine,
and
nitriles
verify
that
these
substrates
act
as
two-electron
donors,
thus
binding
end-on
to
the
titanium
center
give
donor-stabilized
imides
3a,b
4a–c.
Given
potential
of
an
electron
acceptor,
was
reacted
phosphine
oxides
(OPEt3/OPPh3)
according
Gutmann–Beckett
method
get
information
about
Lewis
acidity
yield
5a,b.
Complex
5a
one
rare
examples
structurally
characterized
complexes
η1-bound
cyclopentadienyl
ligand.
Further
insights
into
were
obtained
from
nitrile
adducts
4a–c
through
IR
spectroscopy
NMR
(δ(19F)
1JC,F
employing
4-fluorobenzontrile).
In
reactions
terminal
alkynes,
respective
amido
acetylides
6a,b
obtained,
whereas
internal
alkynes
demonstrate
not
very
prone
undergoing
[2
+
2]
cycloaddition
reactions.
Accounts of Chemical Research,
Год журнала:
2021,
Номер
54(17), С. 3476 - 3490
Опубликована: Авг. 23, 2021
ConspectusTitanium
is
an
attractive
metal
for
catalytic
reaction
development:
it
earth-abundant,
inexpensive,
and
generally
nontoxic.
However—like
most
early
transition
metals—catalytic
redox
reactions
with
Ti
are
difficult
because
of
the
stability
high-valent
TiIV
state.
Understanding
fundamental
mechanisms
behind
processes
key
making
progress
toward
potential
applications.
This
Account
details
recent
in
Ti-catalyzed
(and
-mediated)
oxidative
amination
that
proceed
through
formally
TiII/TiIV
cycles.This
class
built
on
our
initial
discovery
[2
+
2
1]
pyrrole
synthesis
from
alkynes
azobenzene,
where
detailed
mechanistic
studies
have
revealed
important
factors
allow
turnover
despite
inherent
difficulty
redox.
Two
conclusions
(1)
low-valent
intermediates
catalysis
can
be
stabilized
coordination
π-acceptor
substrates
or
products,
they
act
as
"redox-noninnocent"
ligands
metal-to-ligand
π
back-donation,
(2)
reductive
elimination
π-type
electrocyclic
(or
pericyclic)
rather
than
direct
σ-bond
coupling.The
reactive
species
imidos
(Ti≡NR),
which
generated
either
aryl
diazenes
(RN═NR)
organic
azides
(RN3).
These
then
undergo
2]
cycloadditions
alkynes,
resulting
coupled
to
array
other
unsaturated
functional
groups,
including
alkenes,
nitriles,
nitrosos.
basic
reactivity
pattern
has
been
extended
into
a
broad
range
stoichiometric
multicomponent
coupling
small
molecules,
leading
syntheses
various
heterocycles
aminated
building
blocks.For
example,
two
different
leads
pyrroles,
while
nitriles
pyrazoles.
heterocycle
often
yield
substitution
patterns
complementary
those
classical
condensation
routes
provide
access
new
electron-rich,
highly
substituted
heteroaromatic
scaffolds.
Furthermore,
alkyne
carboamination
accomplished
via
yielding
α,β-unsaturated
imine
cyclopropylimine
blocks.
New
methods
such
α-diimination,
isocyanide
imination,
ring-opening
strained
alkenes
continuously
emerging
result
better
understanding
catalysis.Ultimately,
these
-mediated
demonstrate
importance
examining
often-overlooked
elements
like
metals
lens
modern
catalysis:
lack
utility,
frequently
undiscovered
transformations
orthogonal
selectivity
their
late
counterparts.
The Journal of Organic Chemistry,
Год журнала:
2019,
Номер
85(2), С. 327 - 338
Опубликована: Дек. 4, 2019
A
novel
approach
has
been
constructed
for
the
synthesis
of
two
types
2-amino-4-coumarinyl-5-arylpyrroles
(ACAPs,
5
and
6)
through
a
cascade
reaction
metal-free
catalyzed
aerobic
oxidation
arylglyoxal
monohydrates
1,
1,1-enediamines
(EDAMs)
2
3,
4-hydroxy-2H-chromen-2-ones
4
via
multicomponent
reactions
to
produce
target
compounds
with
good
excellent
yields.
Specifically,
hydroxyl-substituted
2-amino-4-coumarinyl-5-arylpyrroles,
that
is,
2-amino-4-coumarinyl-5-aryl-6-hydroxylpyrroles
(ACAHPs)
6,
were
obtained
by
in
1,4-dioxane
at
simple
reflux
approximately
10
h.
As
result,
ACAHPs
6
have
produced
without
metal
catalysts
or
traditional
oxidizing
agents.
This
method
represents
route
obtain
ACAPs
an
environmentally
friendly,
concise,
rapid,
practical
manner
potential
biological
activity
product.
ACS Catalysis,
Год журнала:
2019,
Номер
9(12), С. 11753 - 11762
Опубликована: Ноя. 11, 2019
Simple
Ti
imido
halide
complexes
such
as
[Br2Ti(NtBu)py2]2
are
competent
catalysts
for
the
synthesis
of
unsymmetrical
carbodiimides
via
Ti-catalyzed
nitrene
transfer
from
diazenes
or
azides
to
isocyanides.
Both
alkyl
and
aryl
isocyanides
compatible
with
reaction
conditions,
although
product
inhibition
sterically
unencumbered
substrates
sometimes
limits
yield
when
employed
oxidant.
The
mechanism
has
been
investigated
both
experimentally
computationally,
wherein
a
key
feature
is
that
release
triggered
by
electron
an
η2-carbodiimide
Ti-bound
azobenzene.
This
ligand-to-ligand
redox
buffering
obviates
need
high-energy
formally
TiII
intermediates
provides
further
evidence
substrate
"redox
noninnocence"
can
promote
unusual
catalytic
transformations.
Organic Letters,
Год журнала:
2020,
Номер
22(12), С. 4726 - 4731
Опубликована: Июнь 2, 2020
The
reaction
of
1,2-disubstituted
2-imidazolines
with
electron-deficient
alkynes
proceeds
as
a
pseudo-three-component
process
and
forms
imidazolidines
an
N-vinylpropargylamine
fragment.
Heating
the
resulting
in
xylene
on
air
leads
to
effective
formation
polysubstituted
pyrroles
through
domino
sequence
aza-Claisen
rearrangement/transannular
nucleophilic
addition/oxidative
ring
opening
reactions.
direct
one-pot
transformation
has
been
also
realized.
Current Organic Chemistry,
Год журнала:
2020,
Номер
24(11), С. 1196 - 1229
Опубликована: Май 28, 2020
Pyrroles
are
the
most
prevalent
heterocyclic
compounds,
which
present
as
basic
cores
in
many
natural
products,
such
vitamin
B12,
bile
pigments
like
bilirubin
and
biliverdin,
porphyrins
of
heme,
chlorophyll,
chlorins,
bacteriochlorins,
porphyrinogens.
The
biological
activities
compounds
having
pyrrole
analogs
include
antimicrobial
(antibacterial,
antifungal),
anti-cancer
(anti-cytotoxic,
antimitotic),
anti-tumor,
anti-hyperlipidemic,
anti-depressant,
anti-inflammatory,
antihyperglycemic,
antiproliferative,
anti-HIV
anti-viral
activities.
Accordingly,
significant
attention
has
been
paid
to
develop
competent
methods
for
synthesis
pyrroles
with
improved
yields
short
times.
This
review
gives
an
overview
different
using
easily
available
precursors
following
routes.
Synthesis
monosubstituted
2,5-dimethoxyfuran
dialkylacetylene
dicarboxylate
β-ketoester
1,2-dicarbonyl
1,3-dicarbonyl
1,3-dicarbonyl,
amine,
nitro
aldehyde
group
1,4-dicarbonyl
compound
amines
enones
moieties
acetylene
Chemical Science,
Год журнала:
2021,
Номер
12(28), С. 9574 - 9590
Опубликована: Янв. 1, 2021
In
this
Perspective,
we
discuss
recent
syntheses
of
5-
and
6-membered
aromatic
heterocycles
via
multicomponent
reactions
(MCRs)
catalyzed
by
group
4–8
transition
metals,
with
a
focus
on
common
mechanisms
synthetic
strategies
across
the
series.
