17O-enriched α-azohydroperoxides: 17O NMR spectroscopy, 17O-labeling reagents

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.