Download Convenient Methods for the Reduction of Amides, Nitriles

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Tetmhedron Vol. 48, No. 22, PP.46234628.1992
Printed in Gnat Britain
Convenient Methods for the Reduction of Amides, Nitriles,
Esters, Acids and Hydroboration
AS.
smo+.oo
Pcrgamm Press Lad
Bhanu Prasad,
J.V.
School of Chemistry,
Carboxylic
of Alkenes Using NaBH&System
Bhaskar
University
Kanth
and Mariappan
of Hyderabad,
Periasamy*
Hyderabad
500 134, India
(Received in UK 8 April 1992)
system
in THF
gives the corresponding
Abstract:
Reaction
of amides
with
NaBli4-12
amines in 70-76% yields. Reduction
of nitriles yields the corresponding
amines in 70-75% yields.
The I /NaBH4
system is useful in the hydrobor_ation of olefins and the corresponding
alcohols
The reagent
system is also useful
are o 6 tained
in 78-92%
yields after
H202/?H
oxidation.
for the reduction
of carboxylic
esters and acids to the corresponding
alcohols in 60-9096 yields.
The
NaUH4
does
The
efforts
to
increase
discovery
of
hydroboration
conditions.
lead
to
whicti
the
efforts
of functional
reported
are
groups
that
and arnines
It
reduces
has been
of
Al though,
much
I2 with
attention
the
in
mixture
We wish
that
(10
mmol)
the
corresponding
to
those
R2SeBr2.3
and
It
NaB03
BH3:SMe2,7
reported
observed
that
by olefin
(15 mmol);
regio
BH3:THF,’
addition
here
pure
reduction
corresponding
under
condi-
C2H5)
shown
convenient
and acids
alcohols
reflux
or
has been
for
diborane
accessible
mmol)
2.511 at
1-4
can
reagent
that
and
that
the
procedures
into
for
alcohols
of amine
of carboxylic
and
followed
in Table
NaBH /ZnC12/N,N-diethylaniline
4
hydroboration
of olefins with
the
receive
system
is useful
boranes.5
Addition
of an arnide
by refluxing
I).
by
did not
acid group to alcohol.6
into a mixture
O’C
be oh taincd
system
the 12/NaBH4
preparation
reduction
(entries
of
I2 (2.8
stirring
The
2
yields
in
are
THF
12/NaBH4
observed
mmol)
to
NaBH4
(7
for 2h at room temperature
gives the corresponding
and stereoselectivities
BH3:SMe29
the
(or) imide
for
3h gives
comparable
and
in THF
NaBH4/
followed
give alcohols.’
followed
or H202/NaOAc
that
that
in the
of 12 (IO
yield
for
= CH2CH2Br
It
diborane
and BH3:NR3).
it has been recently
amine
esters
We have reported
in TIHF
70-7696
describe
readily
leads to selective
mmol)
in
using
has been
with
(23
amine
(R
of
acids
system.
utilization
the addition
We have
NaOH
The
NaUH4
reported
by oxidation
O°C
here
for
the
amines.
carboxylic
tilnc
this
applications.
of diborane
of I2 to RCOOH/NaBH4
to report
a long
to
R2SeBr2
We
amines,
in diglyme,
in synthetic
generation
for
of
borane.
to
methods
arnbient
Lewis
generation
For example,
reduced
under
using
BH3:SMe2
of a tertiary
corresponding
using the NaBH4/12
known
NaBH4
a mixture
for
convenient
are
acids
esters
BH3:THF,
additives.
amides
the
gives
nitriles
other
and
towards
methods
(e.g.
in the presence
to
THF
and
has been
and
that
nitriles
and
forms
developing
with
esters
NaBH4
olefins’
for
along
reported
of alkenes
il
of
esters
carboxylic
of
in various
in THF
and
amides
also hydroboration
of
also
nitriles,
reactivity
continuing
acid
system
reduction
reaction
still
amides
R2SeBr2/NaBH4
the
using NaBH4
carboxylic
NaBH4
amides,
available
using NaBH4/ZnC12
tions.2
for
reduce
is now commercially
However,
the
not
alcohols
here
and BH :N,N-diethylaniline
3
are
5
4623
in 78-92%
similar
complexes
to
mmol)
in THF
and oxidation
yields (entries
those
for
reported
(25
with
ml)
1-5 in Table
previously
the hydroboration
a;
H202/
2).
using
of alkenes.
A. S. BHANU PRASAD et
4624
Table
I:
Reduction
S.No.
of amides
and nitriles
using 12/NaBH,,.a
Ph
Ph
3
70°C
1.
(%)
Ph
.I‘
76
(6h)b
=o
o= b
Yield
Productd
Conditions
Temp. (Time)
Substrate
Ph
al.
h N
&ti2Ph
&Ph
2.
PhNCH3COCH3
70°C(3h)C
PhNCH3C2H5
74
3.
PhNHCOCH3
70°C
(3h)’
PhNHC2H5
75
4.
PhCONH2
70°C
(3h)’
PhCH2NH2
70
70°C
(3h)=
5.
CH&N
74
CHpCHINHl
6.
PhCH2CN
70°C
(3h)’
PhCH2CH2NH2
72
7.
PhCN
70°C
(3h)’
PhCH2NH2
70
70°C
(3h)’
CH3(CH2)7CH2NH2
75
8.
a)
The
experiments
and adding
12 in THF
and imide
were
(5 mmof)
used.
(d)
Selective
an
ester
5, Table
(20
were
ml)
out
by
taking
the
in portions
for
2.5h
used. (c) NaBHQ
(23
mmol),
products
hydroboration
group
However,
the mixture
We have
0°C
The
carried
were
of
as illustrated
identified
olefinic
by
the
at 0°C.
can
be
and
NaBHo
(b) NaBl-l@ (27
I2 (IO
spectral
by
group
substrates
mmol)
data
hydroboration-oxidation
fH
when
of
mrnof),
NMR
it
(25
l2 (12
and amide/nitrife
(In,
achieved
in THP
and
is present
mi)
mmof)
(10 mmol)
13C
NMR).
along
methvl-IO-undecenoate
with
(entry
2).
the addition
at
were
for
in 94% yield,
carboxylic
esters
of I2 (5 mmol)
for 0.5h after
also observed
2.5h
followed
indicating
2NaBH4
can
the addition
that
by the
THF
reduced
to
(12 mmol)
addition
of
corresponding
esters
I2 (5 mmol)
of
Ph3P
of BH3:THF
+ 2NaI
the
in THF
of carboxylic
addition
the formation
+ I2
be
and NaBH4
+ Ii2
(10
NaBH,,
mmol)
in the reaction
I
PPh3
PPh3:BH3
for
in
86-g!?%
by
2.5h and refluxing
1 and 3, Table 3).
(entries
to
+ 2BH3:THF
alcohols
(30 ml) at 0°C
(I2
in THF
mmol)
(20
of NaBH4
in THF
ml)
gives
with
12.
(30
ml)
Ph3P:BH3
Reduction using NaBH&
Table
2:
Hydroboration
of alkenes
using 12/NaBH4
in THF.a
Yield
Producte
Conditions
Temp. (Time)
Substrate
S.No.
4625
system
(%)
1.
PhCH=CH2
25°C
(2h)b
PhCH2CH20Hf
90
2.
CgH,2CH=CH2
25°C
(2h)b
CgH, 2CH2CH20H
92
OH
0
3.
\
4.
25°C
(4h)’
85
25°C
(4h)’
81
6
5.
(a) The
the
25°C
experiments
addition
mmols)
mmo])
of
were
were
carried
used
and
and
the
the
(15
mmoi)
The
products
were
identified
with
data
reported
parison
\vaS
20% (‘H
NMR
In all
known
order
the
avoid
0.5h at O’C without
We have
lcads
to
When
the
purified
organoboranes
the
by
were
were
the
data
(IR,
mmol),
chromatography.
was
NMR
(f) Contains
the
reduction
(I and/or
also react
l2 in THF
possible
cleavage
significant
reported
of
of
that
THF.
H202/OH-.
H202/OH-.
followed
by
(b)
Alkenes
(15
(c)
Alkenes
(10
(d)
Olefinic
ester
oxidized
using
H202/NaOAc.
and
NMR)
and also by com-
the
13C
isomeric
(e)
l-phenylethanol
upto
However,
carboxylic
acid
the
this problem
addition
of
can
iodine
by the
to give
slowly
However,
successive
acids.6
from
required
B-1
in portions
the
addition
stoichiometry,
species
which
to NaBH4
time
since
can
are
in THF
it
is
known
at
be reduced
0°C
to
in results.
carboxylic
II) derived
with
was added
of
change
than
addition
1 his method
was attempted
THF
cleavage
I
were
of
RCOOH
gives
in >50
good
mmol
and I2 into
results
scale
in
NaBH4
10
in THF
mrnol
substantial
scale.
amounts
also obtained.
-/-7_OCOR
I
by
‘H
I2 (2.8
using
using
species
literature.
IfiOH
lowed
column
oxidised
oxidised
organoborane
by spectral
in
complexes
recently
reduction
of products
were
organoboranes
and
NaBH,, (7 mmol),
taking
by
, we have used NaBHo more
‘BH3’
ethers.“Also,
to
(2h)d
analysis).
cases
that
to cleave
in
utilized
out
Products
alkenes.
utilized
were
“O-f-GcoocH3
78
CooCH3
-4
II
be circumvented
carboxylic
acid.
The
by the
addition
corresponding
of I2 into
alcohols
are
NaBH4
at 0°C
obtained
in
folgood
A. S. BHANUPRASADet al.
4626
yields
after
in the
the
work
reduction
reduction
acid
into
of
boration
of
(entries
of olefinic
of
3 and
acids
IO-undecenoic
NaBH4
addition
canoic
up
in THF
12 into
the
double
acid (20%)
at
NaBH4
Table
3).
However,
is lost by performing
acid
room
gives
followed
followed
of
the
in this way.
yield
by addition
after
by
acid
(59%)
oxidation
the
with
For example,
0°C6
leads
and
observed
addition
of I2 at
of carboxylic
l,ll-undecanediol
31 are obtained
chemoselectivity
reaction
in 89%
by addition
a mixture
5 in Table
the
IO-undecenol
temperature
at 0°C
bond and
(entry
4,
of
the
However,
to the hydro-
II-hydroxy.
H202/OH-
unde-
and protono-
lysis.
In conclusion,
of amides,
Table
3:
the
nitriles,
Reduction
S.No.
readily
accessible
carboxylic
esters
of carboxylic
esters
Substrate
reagent
12/NaBH4
system
is useful
and acids and also for hydroboration
and acids using 12/NaBH4
in
the
reduction
of alkenes.
in THF.a
Conditions
Temp. (Time)
Yield
1.
PhCH2COOEt
70°C
(0.5hJb
PhCH2CH20H
85
2.
CH3(CH2&COOCH3
70°C
(0.5hIb
CH3(CH2)8CH20H
89
3.
CH3(CH2&COOH
25“C (lh)’
CH3(CH218CH20H
90
Br
r+
4.
(%)
Br
coon
cH#H
25°C (lh)’
8
ti
Br
Br
5.
25°C
86
8
Ho-fK CHzoH
(IhI’
59
20
(a)
Experiments
(12
mmol)
fluxed
were
for
at
were
0°C
0.5h.
isolated
carried
for
(cl
out
2.5h.
The
(b) After
acids
were
by chromatography
fied by spectral
data (IR,
by adding
H
‘
the
addition
added
at
on silica
NMR,
I2 (5 mmol)
gel
General:
Tetrahydrofuran
Infrared
polystyrene
deuterated
are
as
reference.
chloroform
expressed
distilled
spectra
in
ppm
using
freshly
were
NMR
column
the
ml)
the
reaction
mixture
reagent.
(dl The products
12/NaBH4
in portions
(hexane/ethylacetate
eluent)
to NaBH4
was re-
and identi-
benzophenone-sodium
on
a
Perkin-Elmer
were
recorded
silane
as internal
spectra
from
SECTION
over
recorded
tetramethyl
downfield
the ester,
to
(30
13C NMR).
EXPERIMENTAL
experiments.
of
25“C
in THF
the
signal
for
on
a
JEOL-FX-100
standard.
internal
was
used
for
1R spectrometer
Me4Si.
The
For
all
1310
spectrometer
chemical
TLC
shifts
plates
the
with
in
( 5)
coated
4627
Reduction using NaBH& system
with
silica
gel
chamber.
were
For
run
column
in hexane/ethyl
acetate
chromatographic
mixture
purification
and
under
spots were
gravity,
column
developed
grade
in iodine
silica
gel (IOO-
200 mesh size) was employed.
Reduction
(I
g,
27
g,
I2
mmol)
mmol)
mixture
3N
ml).
The
in dry
in dry
was
with
(5
was evaporated
liberate
matography
on
silica
3025,
2900,
gel
7.16-7.68(m,
1600,
15H).
13C
the
and aqueous
amine
borane
The
layer
730,
I,
I)
6:
129.8,
NaOH
MgSO4.
F3B.0Et2
129.0,
(8
(3 x IO ml).
followed
was purified
1.2g
The
destroyed
anhydrous
by chro-
(76%).
3.08-3.6
I2 (3
2.5h.
3N
ether
with
Table
Yield:
139.8,
using
over
was treated
for
carefully
with
and dried
NMR(CDC13)
: 144.9,
MHz)
NMR(25
brine
(entry
‘H
was
of NaBH4
flask.
0°C
neutralized
acetate/85:15).
690.
at
hydride
was
residue
product
round-bottom
was extracted
water,
(hexane:ethyl
1450,
it
to a slurry
atmosphere
excess
ceased,
with
capped
nitrogen
and
washed
amine.
column
2850,
0°C
(15 ml) was added
septem
under
evolution
and the
free
a two-neck
to
gas
were
the
in dry THF
added
cooled
the
extracts
to
2H),
6h;
in
was
was separated
organic
solvent
ml)
ml)
After
layer
g, 5 mmol)
(15
(20
for
by aq.NaOH
3050,
THF
ml).
organic
(1.7
THF
refluxed
HCI
The combined
The
lmide
of imide:
(m,
128.0,
IR(cm-‘1:
6H),
3.96(s,
127.6,
126.1,
63.1, 60.8, 53.8.
Reduction
were
8,
in dry
IO mmol)
2.5h.
The
troyed
lized
THF
in dry
ted
ether
over
2800,
2H),
1600,
(2
Na13H4
THF
(30
for
(8
ml)
was
to
0°C
and
was
brine
gel
750,
MHz)
and
660.
3N
HCI
solvent
gel
690.
slowly
3 g of
with
dried
NaOH
ether
over
organic
and
136.7,
128.5,
In
a
the
was
contents
added.
The
(3 x 10 ml).
1.9
126.5,
THF
The
MgS04.
(s,
41.5,
34.2,
was
layer
was
I.1
2.6(m,
20.9.
was
0.5h.
and
2NH),
2950,
11.0.
flask,
taken
nitrogen
in dry
atmosphere
to O”C, 6N HCI
mixture
and
and
6.54-6.7(m,
the
was
cooled
aqueous
was washed
with
chromatographed
IR(crr~-~):
5.3(bs,
3020,
were
The
extract
brine
round-bottom
under
separated
organic
concentrated
4H),
capped
neutra-
by column
2H),
37.2,
for
des-
was extrac-
lR(cm-‘1:
46.6,
0°C
was
water,
3h. It was cooled
for
g (74%).
it
3.38(q,
10 mmol)
added
for
organic
combined
3H),
septem
refluxed
It
6H),
ml)
at
(2.54
hydride
was purified
(74%).
112.4,
(1.45g,
were
Yield:
Ig
2.84(s,
116.0,
(70°C)
Iodine
layer
with
product
Yield:
(20
ceased,
and the aqueous
3H),
g, 23 mmol)
flask.
atmosphere
was washed
two-neck
(0.88
to O”C, the excess
and the
129.1,
was refluxed
nitrogen
gas evolution
extract
1.12 (t,
: 149.1,
in dry
mixture
anhydrous
NMR(CDC13)6:
the
was removed
MHz)
(hexane:ethylacetate/60:40).
‘H
under
3,5-dimethylbenzylcyanide
mmol)
The reaction
added
After
and NaBH4
round-bottom
3h; cooled
was separated
NMR(CDC13)6:
and
g,lO
capped
(hexane:ethylacetate/95:5).
‘H
13C NMR(25
mmol)
for
ml).
combined
IO mmol)
in portions
layer
The
I2 (2.54
2.5h.
: 138.4,
(6
The organic
g,
septem
(70°C)
The
740,
23
extracted
column
of
(1.49
added
3,5-dimethylbenzylcyanide:
g,
ml).
at 0°C
was
ml).
2H).
of
(0.88
ml)
MgS04.
on silica
7.08-7.24(m,
amide
in a two-neck
was refluxed
(8 ml).
x I5
1450,
Reduction
(20
addition
anhydrous
chromatography
ml)
mixture
by careful
with
(25
THF
reaction
using 3N NaOH
dried
The
of N-methylacetanilide:
taken
3400,
2950,
6.5(s,
3H).
layer
water,
on silica
2800,
13C
1600,
NMR(25
A. S. BHANUFQASADet al.
4628
Hydroboration
7 mmol)
under
of
nitrogen
tion
mixture
added
and
atmosphere
washed
purification
of
2.44(bs,
of
in
I2 (6.4
through
To
this
in THF
The
The
with
3N NaOH
MHz)
Acknowledgement:
to UGC
: 62.1,
We
are
for Special
1050.
to
extent
slowly
the
solution,
36.1,
35.7,
grateful
to
Assistance
32.2,
CSIR,
New
and COSIST
signals
of
2.5h
Ih at
ether
20%
1.
Brown,
Yamakawa,
H.C;
3.
Akabori,
.4.
Freeguard,
5.
Narayana,
6.
Bhaskar
7.
Brown,
8.
Kabalka,
9.
Brown,
Subba Rao, B.C.
T; Masaki,
S; Takanohashi.
G.F;
H.C;
J.V;
Choi,
G.W;
H.C;
10. Narayana,
Long, L.H.
Chem.
C; Kabalka,
& Ind.
25°C.
over
28.5,
26.4,
Delhi
for
(30
DiLHCI
MgS04.
3325,
P.P; Narayana,
Synthesis
1956,
78, 5694.
Sot.
Jpn. 1991,
ml)
(20
2850,
support.
64, 2730.
482.
Chem.
1987,
323,
Chem.
1991,
56, 5964.
C. J. Chem.
via Boranes,
G.W; Tetrahedron
Trans.1 1991,
Wiley
Lett.
1982,
1990,
145.
47, 3153.
Ed., 1990,
Interscience,
31, 6977.
observed.
(2.1
the
g,
slurry
equalizer
was
ml,
Evaporation
financial
Sot.
Chem.
also
added
3N)
The combined
2900,
3H),
and 4.72
was
organic
of solvent
1450,
1050.
25.4.
Chem.
S; J. Org.
1.44(d,
I.44
a pressure
Programmes.
Perkin
1.68 g
To
1965, 471.
M. J. Org.
Narasimhan.
Wadgaonkar,
Organic
Sot.,
M. J. Organomet.
Periasamy,
Y.M;
Chem.
H. Bull.
Y. J. Chem.
C; Periasamy.
Kanth,
J. Am.
M; Nohira,
solvent
NaBH4
REFERENCES
2.
extract
of
at
flask.
in THF
was
was separated
are
through
(3 x 20 ml).
IR(cm-‘):
29.1,
ml)
organic
NMR(CDC13)6:
The
50 mmol)
and dried
g (90%).
(20
evaporation
round-bottom
for
with
brine
15
g,
stirred
was extracted
layer
scale) using NaBH4/12:
during
(17.2
further
‘H
5H).
g,
and the reac-
THF
combined
On
(0.27
(hexane:ethylacetate/90:10),
two-necked
acid
Yield:
52.8,
in
was added
were
layer
IO,ll-dibromoundecanol.
13C NMR(25
taken
The
7.0-7.32(m,
acid (50 mmol
was
contents
1600,
IH),
(2 ml),
The organic
MgSO4.
NaBH4
(15 ml) was added
was added
water
10 ml).
column
I-phenylethanol
(60 ml)
aqueous
gel
3300,
4.72(q,
with
30 ml).
x
flask
in dry THF
g, 15 mmol)
anhydrous
silica
IR(cm-l):
ml)
(3
over
on
2H),
(1.5
(3N,
ether
dried
presence
(120
Styrene
round-bottom
g, 2.8 mmol)
It was quenched
IO,ll-dibromoundecanoic
was washed
thankful
the
THF
added.
afforded
3.7(t,
0°C.
with
IO,ll-dibromoundecanoic
dry
a cannula.
carefully
layer
to
g, 25 mmol)
0°C.
and
isolated.
2H),
capped
(0.71
30 ml)/NaOH
extracted
brine
were
corresponding
mmol)
at
spetem
Iodine
25°C.
chromatography
2.78(t,
60
2.5h
2h at
was
water,
by
alcohols
Reduction
at
layer
with
IH),
for
using H202(30%,
aqueous
was
(25 ml).
over
was stirred
and
(90%)
In a two-neck
in dry THF
and oxidized
the
ppm
styrene:
was taken
67, 975.
New York,
1975.
We
are
also