Chemists learned how to selectively replace the hydrogen on the terminal hydrocarbon fragment

American
chemists have proposed
the catalyst, which
selectively replace
the hydrogen on the hydrocarbon end
snippet various
molecules. A new way
allows you to directly
to important organic molecules
of the simplest
hydrocarbons. Results
research published
in the journal Science.

Selective
substitution of hydrogen in the Balkans
one of the most
interesting problems of modern organic
chemistry. Hydrocarbon
the group is in any organic
the connection is a kind of “skeleton”
molecules. The opportunity
to replace the hydrogen in these groups would open new ways in organic synthesis, for example, would
to synthesize more
connections directly from
of crude oil (mixture
various hydrocarbons).
In practice, however,
to functionalitywith
hydrocarbon fragments
it is not easy. First,
in the molecule, as
not normally one hydrocarbon
group and,
the reaction
ability
they are very close.
Therefore the substitution
not
to conduct a selective —
it will be
occur in all hydrocarbon
groups, and instead of one product
get a mixture of several.
Second, when
carbon-hydrogen (C-H
connection)
quite inert, so their
gap requires tough conditions
irradiation with light or heating to
high temperatures. If
in the original molecule, there are other
functional groups, they can also
react — for example, to oxidize
or utsepitsya.

Chemists
from UC Berkeley under the guidance of
John Hartwig
(John
Hartwig) proposed
catalyst
with which you can selectively
to functionalitywith
hydrocarbon
group
on
end of the molecule.
In
the group of Hartwig has long been studied
process
Borof milirovanie
— interaction
with bis(pinacolato)DIBORANE that
leading to the replacement of one atom
hydrogen on pinacolborane
fragment
(Bpin).
For
activation
WITH-N
links
uses a catalyst — complexes
metal.
Mainly
in this reaction come the end
hydrocarbon groups,those groups
which are deep molecules,
volumetric catalyst
can’t get close.
Interestingly, the C-N connection at the end
the atoms are characterized by high strength,
and in most of the known reactions are
groups usually come in last
turn. Therefore, the possibility of selectively
to functionalitywith end
the hydrocarbon group is
for organic synthesis special
interest.
The
not less
in
previous works outs
reactions
was too
low to
to talk about
their
practical application.

In
new job Hartwig and his colleagues found
a way to speed up the reaction by using the new
catalyst. They
tested
several catalysts based on
complexes of iridium with aromatic
ligands, the most effective
turned out to be complex
with 2-methylphenanthrene.
It
increased
speed
reaction
more
than
50 times, at
this selectivity was observed
high.
Using
this catalyst that the authors
able to selectively replace end
atom in
the molecule n-dodecane
WITH12H26

linear
alkanes, consisting of twelve atoms
carbon. The reaction occurs at
regarding
soft
conditions (temperature
100
degrees Celsius, two
or a three-fold excess of bis(pinacolato)diboron)
with
65%
output. In
the result
only two products — mono – and disubstituted
dodecane in the ratio of six to one
which
easy
to separate from each other.
For comparison: if you functionalitywith
n-dodecane
traditional nonselective
way

for example,
using radical chlorination —
it
will lead to the formation of six
isomers monoslideshow
product
forty-two isomers
nizamedinova product, as well as many
poliducto.
To share
this mixture of products
it
would be extremely
difficult.

With
using the proposed method
to functionalitywith a large number of
different
compounds
end-hydrocarbon fragment

Bpin
always replaces a hydrogen in this fragment.
In addition
also
this approach allows to selectively
to functionalitywith saturated
heterocycles
— cyclic soedineniya,
which contain one non-carbon
atom, usually nitrogen, oxygen or sulfur. In
this case replaces a hydrogen on the second
carbon, counting from non-carbon
atom.
Below
to demonstrate the versatility
approach, the authors selectively
have functionalitywise
36
various
substances
with outputs ranging from 29 to 90 percent. (Output
29 percent in organic chemistry
considered to be quite low, however
the authors note that they did not spend
full optimization of conditions of each
response. In
further these
the parameters can be improved).
When
this bilirubina
does not affect other functional
group
the source molecules.

In addition
the authors demonstrated that
pinacolborane
group
received product
it’s easy to replace,
entering her place, to
example,
hydroxyl
group
halogen
or a hydrocarbon fragment. This
a new approach
opens
many
opportunities
in organic synthesis
for example, it
can
selectively
to
functionalized molecules
the simplest hydrocarbon
raw materials.

A few
years ago, American chemists
developed
another
the catalyst
on
basis of complexes of iron,
which
allows
aimed to modify certain
the plot of three natural amino acids
Proline, valine and
leucine. With
it
can be used to obtain different
artificial amino acids available
natural, which is much faster than
to synthesize them from scratch.

Natalia Samoylova

Leave a Reply

Your email address will not be published.