Tetrahedron Letters,Vol.26,No.l7,pp 2051-2054,1985 Printed in Great Britain
170-ENRICHED
A.L.
a-AZOHYDROPEROXIDES:
0040-4039/85 $3.00 + .OO 81985 Pergamon Press Ltd.
I70 NMR SPECTROSCOPY,
Baumstark,*P.C. Vasquez and P. Balakrishnan,
and Laboratory
for FBS, Georgia
State Oniversity,
170-LABELING
Department Atlanta,
REAGENTS
of Chemistry
Georgia
30303 IJSA
Summary: l7 -enriched a-azohydroperoxides, prepared by autoxidation, are efficient 170-labeling "0 NMRI (CD3CN) of 2 showed broad signals at 6 264 and 204 PPM; reagents; the solvent dependence of the 7O chemical shifts and the kinetics of ionic oxidations are interrelated. Despite shift
the
range
Recently,
a
conjugated
relative
makes
it
number
oxygen
of
of
organic
most
hydroperoxide,
(unstable)
organic
a unique
solvent
atom
transfer
chemistry4
azohydroperoxides
shift
We
are important,
was
report
the
the corresponding gen
11 Cas well
of peroxides
the only reported to
show
170
NMR
data
chemical
molecu1es.I and
non-
and hydroper-
I70 NMR spectrum one
on
broad
for
170-enriched
a-
of the hydroperoxides
were found to
are of high reactivity chemistry?,
siqnal
at present,
in oxygen-
170-enriched
a-
reagents.
1
_,f
-
-
R2C(OH)-N=N-R
+ X=0
a-Azohydroxide
phenylhydrazones
XC6H4-CH=N-NHPh
on conjugated
as in free-radical
new 170-labeling
a-azohydroperoxides,
(Rxn 11. Enrichments
studies
found3b
first
a-Azohydroperoxide
170-enriched
large
in organic
I70 NJ@ studies
Furthermore,
the
bonding
l70 NMR data can not be obtained,
Scheme
+ X
correlation
Since a-azohydroperoxides
(Scheme
spectroscopy,
of
shift data for both oxygens
dependence.
R2C(OOH)-N=N-R
study
hydroperoxide,
abundance
peroxides.
in NMR
the
However,
reports.3
t_butyl Natural
The chemical
show
chemical
to isolated
oxygen
for
have appeared.2
Hz) at 260 ppm.
azohydroperoxides.
of
nucleus
substituent
have been limited
an
receptivity
important
systems
oxides
(VI/~ -1000
low
an
of -10
+
l-3, were prepared
with one equivalent
atom % 170 were
CgD6 *02 m
in 80% isolated yields
of 20 atom % 170-enriched
routinely
XC6H4-;H-N=N-Ph
achieved.
1, X=p-MeO;
The 170 Nm
by oxidation molecular
of
oxy-
spectra of the
2, X=H; 3, X=1-Br
(11
O-OH ** 170-enriched shows
a-azohydroperoxides
a composite
signals resolved
were
poorly
signals
(l-3) were taken in C6D6, CD3CN,
of the 170 NMR spectra resolved
for
(VI/~-1500-1800
all
for 2 that
three
Hz) were
compounds.
observed
2051
and CH3OH at 31 il"C. Figure
is representative.
In C606,
the
1
I70 NMR
In CD3CN and CH3OH, two broad, well-
(all cases).
The
170 chemical
shift
data
2052
seem
to
depend
C6D6, the by
"hydroperoxy"
Addition
of
identical
5%
protons
CD3CN
to those
hydrogen-bond
in
to
solutions
involved.
C6D6
CD3CN,
disrupted
plus
In the case
X
r
6(PPM,
the a-azohydroperoxides.
to the azo function
to the
solvent
the
solvent
to
important.
170-NMR
again
the
In
(determined
becomes
yielded
of CH30H as solvent,
of
spectra
the internal
"peroxy"
oxygen
is
in Table 1.
Table 1. 170 Chemical Shift Data for XC6H4-CH(D&H)-N=N-Ph No.
with
the a-azohydroperoxides
hydrogen-bonding
The data are summarized
solvents
hydrogen-bonded
hydrogen-bonding of
in CD3CN as solvent.6
is
of the
are internally
However,
spectroscopy).
IR
interactions
on the specific
C6Od
6(PPM,
CD7CN)
at 31°C. 6(PPM,
CH?OH)
e_MeO
~245~ -215a
251
206
275
204
2
1-H
245
215
254
204
266
200
3
e-Br
245
213
249
196
254
195
-3000 Hz, not resolved at 31°C. a) v1/2 Due to the large v~,~'s for the 170 signals for the a-azohydroperoxides and the be
resulting
correlated
tentative
with
for a-azohydroxides
"hydroperoxy" pendence
solvent
that
The
observed
sensitive tional
volving
to
that
equilibria
from toluene
enrichment conditions. equivalent phosphines,
Enrichment
sulfides
phosphine
in Table 2.
oxides
170 chemical
have been
It seems
also produced to various
clear
that
effects the
oxidation
oxygen
systems. However,
is unclear.
showed -5 PPM shielding hydrogen-bond
("hydroperoxy"
170-enriched
sug-
For example,
in changing
u-azohydroperoxides
solvent
1).
constitute
substrates.
a
Most
out under equilibrium
generally
For example,
(Scheme
Reuben
in cases in-
of the a-azohydroper-
of 170 into organic
a-azohydroperoxides
in high yield
on
oxygen).
H20 and are carried
solvents.
1. Effect of solvents
the 170 NMR data for 2.
effects.
by a-azohydroperoxides
the 170-enriched
Figure
addi-
sites, the situation
of the internal
of
is
to be
in saturated
for the incorporation
and sulfoxides
shifts
deshielding
alcohols
out in aprotic
with
with
of the
shown1s2a*3a,8
the use of 170-enriched
via ionic
and can be carried
de-
proton
hydrogen-bonding
of the
reactions
method
involve
solvent
deshielding.
2e for benzyl
transfer
procedures'
and
while
Thus, disruption
economical
from that of the
in deshielding3a,8a
donation
data
A
signal
Hz), would indicate
"hydroperoxy"
could result in shielding
oxygen-atom
efficient,
epoxides,
shift
the
of the observed
effects.
or hydrogen-bonding
to acetone.
by solvent
The
shifts
results
that
is downfield
of the
dependence
hydrogen-bond
can not
alcohols.2e
in accord with the above assignment,
effects
NMR chemical
the signals
benzyl
PPM (v~,~ -450
oxygen produces
hydrogen-bonding
the I70 chemical
listed
shielding
for
observation
shift
shifts,
hydrogen-bonding
gested8a
new,
chemical
solvent
170
the
An interpretation
to the "peroxy"
intriguing.
on
hydrogen-bonding
in
shifts,
obtained
is seen at -27 oxygen
oxygen.
results
solvent
oxides
based
of the chemical
require
in chemical
results
assignment,7
that the "peroxy"
would
error
the
requires
the oxidation yielded
the
Representative
only one
of alkenes, 170-labeled results
are
2053
Table
2.
Isolated with
Product
Yields
170-Enriched
and
170
NMR
a-Azohydroperoxides
(Scheme
95
44(Jp_o=169
Me2S PhSMa
90
12
PhS(*O)Me
81
Me2c=cMe2
~2C;/c~2
Yield
by 170-NMR
for the oxidation
slowed
of BzSMs
in CD3CN 3.
relative
to those
of Solvents
oxidations. contrast
were
obtained
On the other hand, the results
1 at 32".
CD30H
1.6*0.2~10-~
1.1
C6D6
7.3*0.2~10-~
1.0
CD3CN
3.1*0.2x10-3
0.4
CD30H
4.4*0.2x10-*
showed
an
increase. of
analogous
Similar
the a-azohydroperoxides
results
of peracids.g
effect
rather than a change 170-enriched
reagents.
pounds.
The I70 Nt@ spectroscopy
for the two oxygens
The 170-enriched
oxygen
(Scheme
method
overnight. of
oxygen
effects
There
Additional unlabeled
O2
as solvent,
of the
slow
the data
with the 170 NFR data,
be readily
appears
of
sealed
positive
the
were
the
are
in
suggests
charge the
(in the
solvent
flask.
shows that the chemical
as follows:
(a
The
to 100 mg (0.51 mnol)
occasionally
syringe.
mixture
was
to keep a positive
progress
was
monitored
com-
the 17D
reactions.
15 ml_ (-0.5 nol)
reaction
as 170-
shift data
between
transfer
added via a gas-tight
Reaction
and used
for selected
to be a correlation
25 mL flask,
pressure.
added
prepared
and economical
data for oxygen-atom
were prepared
N2 gas was into
should
of the developing
efficient
on kinetic
(MSD Isotopes)
a slight
(solvent)
hydrogen-bonding
of the a-azohydroperoxides
a-azohydroperoxides
to achieve
can
is highly
dependent.
and solvent
molecular
in CD3OH
1) by
6.0 disruption
in basic process).
in 3 mL C6D6 in an evacuated,
via syringe
CD3CN
consistent
a-azohydroperoxides
labeling
are solvent
dependence
by
be expected
Rel. React.
on peracids,
may be due to the stabilization
"peroxy"
labeling
This
would
An interpretation,
"catalytic"
In conclusion,
to observations
in are
in the polar, protic
by a-Azohydroperoxide
1.0
sulfoxide
data
show that the oxidations
0.16
the
leakage
with a-azohydroperoxides data clearly
state
The kinetic
1.5tO.2xlC+
in CD$H
reduce
chemistry.
a
differences
2.4*0.1~10-~
on
dark
transfer
to
transition
the hydrogen-bonding
c6D6 CD3CN
state)
the
in the
ascribed4
epoxide
transition
added
Thus,
been
Me2c=cMe2
While
% 170-enriched
has
k$&?
hydrogen-bond
phenylhydrazone
oxidations
(hydrogen-bonding)
The kinetic
in C6D6.
1. 5xln-5 b) fl PPM.
Solvent
to those
solvent
transfer
ionic
on the Ionic Oxidations
that the rate effects
Nm
1.3x10-3
Product
(CD30H)
intramolecular
fast
Substrate
BzSMe
solvent
in
of peracids9).
3).
Hz)
1.3x10-2
% 170.
should affect oxygen-atom
(Table
Compounds
k,M-lsec-l
0.6
13*t2atom
and 2,3-dimethyl-2-butene
solvents
Effect
proton
to that
spectroscopy
differing
Table
(similar
(%)
60 a)
of a-azohydroperoxides
intramolecular
occur
Organic
I70 &(PPM)b
Me2s(*o)
reactivity
of
in C6D6 at 32°C.
Ph2P(*O)Me
in which
the three
Oxidation
Ph2PMe
1) can
observed
the
Product
high
mechanism
for
Substrate
0* The
Data
benzal
of PO atom N2 oas was stirred
in
pressure
to
by
'H NMR
2054
spectroscopy.
After
azohydroperoxide. recrystallized
completion
The
yellow
of
the
reaction,
pentane
was
solid
was
collected
(in the
dark),
from benzene/pentane,
13 f 1 atom % 170].
The spectral
and stored
and physical
The 170 NMR spectra were recorded band probe operated were
at 36.5 MHz.
0.2 M_ in C6D6,
external
deionized
points, time.
90" pulse
angle
The spectra
noise
ratio was
were
points.
scans)
for
estimated
(28 us
Under
pulse
by applying
azohydroperoxides
in chemical were
by column chromatography taken
on the
isolated
used.
After
lo3 scans
carried
typical
is k3 PPM.
out according
products
cold
to published
KHz
a-azohydroperoxides
spectra
delay,
broadening
and
to
2 K data
33 ms acquisition The signal-to-
FID prior to
factor to the
after -3 hrs.
band widths reactions
procedures.4
as above except
width,
to kO.2 PPM by zero filling to 8
height
determined
values.4
at 31 f 1°C and referenced
of 20/l were achieved half
the apentane,
with a 10 mn broad
non-decoupled.
The 170-labeling
and the atom % enrichments 170-enriched
and were
was improved
S/N ratios
despite
30.12
200 us acquisition
a 50 Hz exponential
conditions,
shift
were:
spinning
The data point resolution these
the a-azohydroperoxides error
sample
equipped
atom % 170-enriched
were acquired
settings
width),
with
precipitate with
4a at -70°C [isolated yield RO%,
Spectrometer
of the-10
The spectra
instrument
recorded
improved
Fourier transformation. K data
The
to
washed
data were in accord with literature
on a JEOL GX-270
The samples
CD3CN, and CH30H. water.
(wet, CAUTION!)
added
of -1500
with
that 0.03 E
Hz.
170-enriched
Products
by MS analysis.
(-lo4
were
The a-
isolated
170 spectra were
SOlUtiOns
in C6D6 were
(-10 min) S/N ratios of 20/l were obtained.
ALB is a fellow of the Camille and Henry Dreyfus Foundation 1981-1986. Acknowledgement. Partial support for this work was provided by the GSU Research Fund. Mass spectral data were obtained at the Georgia Institute of Technology on an instrument supported in part by the NSF. References
1.
Fo_
PI-
_
_..___L
_A..1_..
_-__
"intzinger,
and Notes
NMR of Newly Accessible
Nuclei,
Vol.
2, Academic
‘es., pp 79-104, 1983,
2. a) T.E. St. Amour, M.I. Burgar, B. Valentine, D. Fiat, J. Am. Chem. SOC. (19811 103, 1128; b) R.R. Fraser, A.J. Ragauskas, J.B. Strothers, ibid, (lm LO4 64/5; c) R.T.C.Townlee, M. Sadek, D.J. Craik, Or . Ma n. Reson. (1983) 21,616; d) D.S;-draik, G.C. Wenz, R.T.C. Brownlee;,Jilt-4g). $em.+~i; e) P. makrishnan, A.L. Baumstark, D.W. Boykin, Tet. f) E.L.miel, K.-T. Liu, S. Chandrasekaran, Or . Ma n. Reson. (1983)T m i. Suoawara, Y. Kawada, H. Iwamura, Bull. Chem _ CI) -, M. Kam: .&&! $ck37 3. a) J.P. Kintzinger, "NMR Basic Principles and Progess," ,P. Diehl, H.R. Schneider, H. Kosfeld, pp. l-64, Springer, Heidelberg, 1981; b) H.A. m Dahn, Helv. Chim. Acta (1961) 44, 865. 65; b) A.L. Baumstark, P.C. Vas4. a) A.L. Baumstark, P.C. Vasquz J. Org. Chem. (1983) 5, quez, Tet. Lett. (1983) 123. 5. E.Y. Osei-Twum, D. McCallion, A.S. Nazran, R. Panicucci, P.A. Risbood, J. Warkentin, (1984) 49. 336: b) T. Tezuka, N. Narita, W. Ando, S. Oae, J. Am. them. Sot. (1981) 103, 3 of- CU3CN was ihown to produce better separation of the twosignals and not 6. AClditix ' of the signals. 0 NMR spectrum (CD3CN) of the perbenzoate of 2, prepared by reaction of 2 with benzoyl 7. I;hcer"@ng Since the effect of benzoylation on the chloride, showed signals at 6 247 and 450 PPM. a) chemical shift of the "peroxy" oxygen is unknown, there are two possible conditions: benzoylation of the hydroperoxide has essentially no effect on the chemical shift of the "peroxy" oxygen (-250 PPM deshielding effect on the adjacent oxygen) or b) benzoylation has __ In nnrr .4^^L~^,A:...^ ^cc^-+ _.. +b.r. U,,,,.,.rll ,.Y%,“,-,../,.,‘Xln DDM,inchialAinn ,.,ffc.r+ nn thn If condition a) is true, then the assignment iS Correct. adjacent oxygen). b) D.W. Boykin, A.L. Raumstark, 8. a) J. Reuben, J. Am. Chem. Sot. (1969) 91, 5725; krishnan, ~$&$.$&ingaf:;;~;;roxides" 9. D. Swern,
(Received in USA 23 October 1984)
Vol.
II pp. 450-475
and references
P. Bala-
therein.