Kinetic study of the radical azidation with sulfonyl azides

Article abstract of DOI:10.1071/CH12523

Rate constants for the reaction between a secondary alkyl radical and two different sulfonyl azides were determined using bimolecular competing radical reactions. The rates of azidation were determined by competition with hydrogen atom transfer from tris(trimethylsilyl)silane ((TMS)₃SiH) of the 4-phenylcyclohexyl radical. 3-Pyridinesulfonyl azide and trifluoromethanesulfonyl azide were found to have rate constants for azidation of 2×10⁵M^-1s^-1 and 7×10 ⁵M^-1s^-1 at 80°C, respectively.

Full text of DOI:10.1071/CH12523

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2013, 66, 341–345
Full Paper
http://dx.doi.org/10.1071/CH12523
Kinetic Study of the Radical Azidation with Sulfonyl Azides*
A
,
A B
Karin Weidner and Philippe Renaud
A
University of Bern, Department of Chemistry and Biochemistry, Freiestrasse 3,
CH-3012 Bern, Switzerland.
B
Corresponding author. Email: philippe.renaud@ioc.unibe.ch
Rate constants for the reaction between a secondary alkyl radical and two different sulfonyl azides were determined using
bimolecular competing radical reactions. The rates of azidation were determined by competition with hydrogen atom
transfer from tris(trimethylsilyl)silane ((TMS) SiH) of the 4-phenylcyclohexyl radical. 3-Pyridinesulfonyl azide and
3
5
ꢁ1 ꢁ1
5
ꢁ1 ꢁ1
trifluoromethanesulfonyl azide were found to have rate constants for azidation of 2 ꢀ 10 M
s
and 7 ꢀ 10 M
s at
8
08C, respectively.
Manuscript received: 25 November 2012.
Manuscript accepted: 18 December 2012.
Published online: 25 January 2013.
Introduction
[7]
Scheme 1, eqn 1), cyclization–azidation, (Scheme 1, eqn 2)
(
and azidosulfonylation.
[
14]
Organic azides due to their kinetic stability are often considered
as protected primary amines that can be revealed by an easy
reductive process. On the other hand, organic azides are highly
energetic compounds presenting a unique synthetic versatility,
illustrated for instance by their conversion to nitrenes (Curtius
rearrangement), their use in dipolar cycloaddition, and their
The mechanism of the radical azidation involves addition of
the radical at the terminal nitrogen atom of the azide followed by
[
15]
rapid fragmentation of a sulfonyl radical (Scheme 2).
The
first step of the carboazidation process, i.e. the radical addition
to the sulfonyl azide leading to the triazenyl radical is irrevers-
ible and its rate (rate constant k ) will be crucial to determine the
[
1,2]
involvement in intramolecular Schmidt reactions.
The
N
classical preparation of organic azides involves a substitution
reaction between an inorganic azide such as sodium azide and
electrophilic alkyl halides and related compounds. A few years
ago we reported a free radical procedure to prepare azidoalk-
nature and the yield of the product. In order to get a better
understanding of this reaction and to design new cascade
reactions involving a final azidation step, it was of great interest
to have some information about the rate constant k . We report
N
[
3]
anes. The reaction involves alkyl radicals generated from
haloalkanes,
here an estimation of the rate constant k for the azidation of a
N
[4,5]
[6]
carboxylic acid derivatives, and organobor-
[
7]
anes and alkyl- or arylsulfonyl azides as radical traps. Carreira
and co-workers also reported the use of arenesulfonyl azides in
their radical mediated cobalt catalyzed hydroazidation reac-
ꢃ
ꢀ
kN
ꢃ
•
ꢀ
R
•
ꢀ
NꢃNꢁNꢃSO Y
2
NꢁNꢁNꢃSO Y
2
R
[8–10]
ꢃ
•
ꢀ
kf
tion.
Free radical reactions not only allow the mild intro-
NꢁNꢁNꢃSO Ar
RꢃN3
ꢀ
YSO2•
2
duction of azides, but they are also compatible with a large
number of functional groups. Moreover, they offer unique possi-
bilities to perform sequential transformations such as for instance
R
Y ꢁ alkyl, aryl
[
15]
[11–13]
Scheme 2. Mechanism of the radical azidation.
intermolecular radical addition–azidation (carboazidation)
PhSO N (3 equiv.)
N3
2
3
(
Bu Sn) (1.5 equiv.)
3 2
ꢀ
EtO C
I
C H
6 13
(1)
2
EtO C
C H
6 13
2
t-BuONꢁNOt-Bu (0.06 equiv.)
C H , reflux
6
6
79 %
(
1) CatBH (neat)
(2)
N3
(2) PhSO N (3 equiv.)
2 3
t-BuONꢁNOt-Bu (0.1 equiv.)
DMF, 80ꢂC
β–citronellene
45 % (trans/cis 9:1)
[13]
Scheme 1. Radical mediated carboazidation
(eqn 1) and hydroazidation (eqn 2).
*
This paper is dedicated to the memory of Professor Athel L. J. Beckwith, a grandmaster in organic free radical chemistry.
Journal compilation Ó CSIRO 2013
www.publish.csiro.au/journals/ajc

3
42
K. Weidner and P. Renaud
I
H
N3
(
TMS) SiH (42 mM)
3
RSO N3 (6–38 mM)
2
ꢀ
t-BuONꢁNOt-Bu
80ꢂC
2
3
1
(3.3 mM)
SO R
2
•
N3
N3
RSO N3
2
kN
ꢃRSO2
•
•
3
3
H
(
TMS) SiH
3
kH
2
Scheme 3. Competition experiment for the 4-phenylcyclohexyl radical involving RSO
2
N
3
3
and (TMS )SiH.
secondary alkyl radical with 3-pyridinesulfonyl azide and
trifluoromethanesulfonyl azide.
The kinetic experiments were run under pseudo first order
kinetic conditions (i.e. a large excess of the two radical traps
relative to the radical precursor was used and the concentrations
of the former reagents were considered as constant during
Method
the reaction). The unknown rate constant k is then given by
N
[
16]
The use of a radical clock
(unimolecular reaction) was ini-
Eqn 1.
tially foreseen but proved to be complex due to the requirements
of the azidation process. The reaction has to involve a secondary
alkyl radical (primary radicals are less efficiently azidated) and
the conditions used for the experiments involved the use of
hexabutylditin to mediate the reaction (see Scheme 1, eqn 1).
Since tributyltin radicals are known to react with sulfonyl
½
ðTMSÞ SiHꢂ ½3ꢂ
3
kN ¼ kH
ð1Þ
½
RSO2N3ꢂ ½2ꢂ
Fixing the concentration of (TMS) SiH, a series of experi-
3
ments using different concentrations of sulfonyl azide furnishes
a mixture of compounds 3 and 2. A plot of the ratio [3]/[2]
[
17]
[18]
azides
and with alkyl azides,
we anticipated that
unwanted reactions could importantly modify the product ratio.
[
7]
against the concentration of the azidating agent, RSO N ,
2 3
A second approach via an organoborane radical precursor also
proved difficult to realize since selective monohydroboration of
a diene is required. This is possible if a terminal alkene is
involved (generation of a primary alkyl radical; see Scheme 1,
eqn 2) but much more difficult with non-terminal alkenes for the
generation of a secondary alkyl radical. In order to keep the
system as simple as possible, we decided to perform a simple
competition experiment involving a well studied radical trap.
The use of tributyltin hydride was investigated first but rapidly
discarded due the fact that tributyltin radicals react with alkyl/
theoretically furnishes a straight line, the slope of which is
directlyrelatedtothe relativerateconstants asdescribed byEqn 2.
kN
slope ¼
ð2Þ
kH ½ðTMSÞ SiHꢂ
3
The rate constant kH for the reaction of a secondary alkyl
radical with (TMS) SiH at 808C can be obtained from the
Arrhenius expression reported for the reduction of 1-methyl-5-
3
ꢁ1
[18]
[17]
hexenyl radical (Eqn 3) where y ¼ 2.3RT kcal mol (1 kcal
aryl azides
ducible product ratio. The use of tris(trimethylsilyl)silane
(TMS) SiH), which is also a slower reducing agent than
and sulfonyl azides
and led to poorly repro-
ꢁ
1
ꢁ1
mol ¼ 4.186 kJ mol ) and the errors correspond to 95 %
[
21]
confidence limits.
(
3
Bu SnH, is expected to alleviate this problem. Interestingly, the
3
logðkH =ðMꢁ
1 ꢁ1
s
ÞÞ ¼ ð8:29 ꢃ 0:48Þ ꢁ ð4:29 ꢃ 0:63Þ=y ð3Þ
tris(trimethyl)silyl radicals are known to be rather unreactive
towards alkyl azides and reliable kinetic data are available for
[
18]
the reduction of secondary alkyl radicals with (TMS) SiH.
3
From this Arrhenius function, a rate constant for the bimo-
Reaction of the triethylsilyl radical with azides has been
19]
lecular hydrogen atom transfer from (TMS)
3
SiH to a secondary
ꢁ1 ꢁ1
s at 808C could be
[
5
reported.
However, this process is too slow to compete with
alkyl radical of k
calculated.
H
¼ 4.3 ꢀ 10 M
the close to diffusion-controlled iodine atom abstraction
between the tris(trimethyl)silyl radical and cyclohexyl iodide
The appropriate concentrations of reducing and azidating
agents were established in preliminary experiments. The reac-
tions were initiated with di-tert-butylhyponitrite in refluxing
benzene. The ratios of azide 3 and alkane 2 were determined by
gas chromatography analysis after calibration of the method
with authentic samples (see Supplementary Material).
9
ꢁ1 ꢁ1 [20]
(
k . 4 ꢀ 10 M
s ). trans-4-Phenylcyclohexyl iodide was
selected as a radical precursor in order make possible a precise
and reliable quantification of the two products (phenylcyclo-
hexane and 4-phenylcyclohexyl azide) by gas chromatography
(
Scheme 3).

Radical Azidation with Sulfonyl Azides
343
0
0
0
0
0
0
0
0
.8
.7
.6
.5
.4
.3
.2
.1
0
3.0
2
2
1
.5
.0
.5
Slope ꢁ 48.1 ꢄ 2 Mꢃ1
Slope ꢁ 16.0 ꢄ 1 Mꢃ1
1
0
.0
.5
0
0
0.010
0.020
0.030
0.040
0.050
[
PySO N ] [M]
2 3
Fig. 1. Azide 3/alkane 2 product ratios as a function of the concentration of
PySO in presence of (TMS )SiH (42 mM). Determination of the rate
at 808C.
0
0.010
0.020
0.030
0.040
0.050
2
N
3
3
[CF SO N ] [M]
3
2 3
constant k
N
Fig. 2. Azide 3/alkane 2 product ratios as a function of the concentration of
CF SO in presence of (TMS )SiH. Determination of the rate constant k
at 808C.
3
2
N
3
3
N
Results
3
-Pyridinesulfonyl Azide
The first series of measurements were made with
-pyridinesulfonyl azide (PySO N ), a reagent frequently used
3
significant enough to indicate that for difficult azidation
reactions of secondary and probably also tertiary alkyl radicals,
the use of a more electrophilic reagent may help to achieve better
results.
2
22]
3
[
for the carboazidation process. This reagent is often preferred
to benzenesulfonyl azide since the excess is easier to remove
from the reaction mixture by straightforward extraction. For
these experiments, the reactions were run at 808C in benzene
using 1 (3.3 mM), (TMS) SiH (42 mM), and PySO N (con-
3
2
3
Conclusion
centration ranged from 6.2 to 38 mM). The ratios of azide 3 to
alkane 2 relative to the concentration of the PySO N are
reported in Fig. 1 and gave a reasonable straight line. Linear
Both 3-pyridinesulfonyl azide and trifluoromethanesulfonyl
azide are fast azidating agents for secondary (and likely tertiary)
2
3
5
ꢁ1 ꢁ1
alkyl radicals, reacting in the 10 M
08C. These k values are in an ideal range to be efficiently
s order of magnitude at
regression of the data yields k /(k [(TMS) SiH]) ¼ 16.0 ꢃ
N
H
3
8
ꢁ
1
N
1
0
M
, and thus an estimate for the rate constant k ¼ 2 ꢃ
ꢁ1 ꢁ1
N
involved in radical chain azidation and carboazidation
processes. They support nicely the numerous synthetic appli-
cations using sulfonyl azides for a final azidation step.
5
.5 ꢀ 10 M
s
(808C) for the azidation process.
Trifluoromethanesulfonyl Azide
[
23]
Trifluoromethanesulfonyl azide (CF SO N )
has been
recently used for a unique desulfitative carboazidation reac-
Experimental
3
2 3
General
[24]
tion.
This reagent represents the most electrophilic species
NMR spectra were recorded on a Bruker Avance 300 spec-
1
trometer operating at 300 MHz for H and 75 MHz for C in
used so far in carboazidation processes and is therefore expected
to be the fastest reagent for azidation of nucleophilic radicals.
Competition experiments involving 1 (3.3 mM), CF SO N
13
CDCl and on a Bruker Avance 400 spectrometer operating at
3
3
2
3
19
76 MHz for F. Chemical shift data are reported in units of
3
(
11–44 mM), and (TMS) SiH (42 mM) were run at 808C. A good
3
d (ppm) using as the internal standard CHCl (d ¼ 7.26 for
3
linear correlation between the ratio 3/2 and the concentration of
CF SO N was observed, yielding k /(k [(TMS) SiH]) ¼
1
13
19
H NMR spectra, d ¼ 77.0 for C NMR spectra). F NMR
3
2
3
N
H
3
chemical shifts are given in d (ppm) relative to the internal
ꢁ
1
4
8.1 ꢃ 2 M from which the rate constant for the azide transfer
ꢁ1 ꢁ1
N
standard CFCl (d ¼ 0.0). Coupling constants, J, are reported in
5
3
was estimated to be around k ¼ 7 ꢃ 1 ꢀ 10 M
s
at 808C
Hz. Infrared spectra were recorded on a Jasco FT-IR-460 Plus
spectrometer equipped with a Specac MKII Golden Gate Single
Reflection Diamond ATR System and are reported in wave
(
Fig. 2).
ꢁ
1
Discussion
numbers (cm ). Mass spectra were recorded on a Waters-
Micromass-Autospec Q spectrometer in the EI mode (70 eV).
High resolution mass spectra were recorded on a Finnigan MAT
In our measurements, several approximations have been made.
For instance, the concentrations of the sulfonyl azide
and the silane during the reaction are not strictly constant.
95 double-focussing magnetic sector in the EI mode (70 eV).
˚
Flash column chromatography was performed on silica gel 60A
Moreover, the value of k used in our calculations was deter-
H
(40–63 mm). Reactions were monitored by thin-layer chroma-
mined for the acyclic secondary radical 1-methyl-5-hexenyl and
may slightly differ for a cyclohexyl radical. Importantly, the
competition experiments gave clean products without
significant formation of by-products. Nevertheless, the values
determined here are believed to represent a useful estimate of the
rate constants for the azide transfer from sulfonyl azides.
Trifluoromethanesulfonyl azide was found to react approxi-
mately three times faster than 3-pyridinesulfonyl azide with the
tography (TLC) carried out on Merck silica gel 60 F254 ana-
lytical plates using UV light as visualizing agent and/or cerium
ammonium molybdate (CAM), or potassium permanganate as a
developing agent.
3-Pyridinesulfonyl Azide
This was prepared according to the reported procedure; physical
[
and spectral data were in accordance with literature data.
22]
4
-phenylcyclohexyl radical. This difference of reactivity is

3
44
K. Weidner and P. Renaud
[
23]
Trifluoromethanesulfonyl Azide
128.4, 126.9, 126.2, 43.8, 36.6, 36.0, 30.1. IR (neat) n ¼ 3024,
ꢁ
1
930, 1490, 1436, 1220, 1150, 992 cm . MS (EI) m/z (%) 286
2
A solution of sodium azide (1.30 g, 20.0 mmol) in water (5 mL)
was cooled in an ice-bath and treated with benzene (3.3 mL).
The resulting biphasic system was stirred vigorously before
triflic anhydride (2.52 mL, 15.0 mmol) was added dropwise.
The reaction mixture was further stirred at 08C for 2 h and then
the temperature was raised to 108C and the biphasic system was
stirred for an additional 1 h. The reaction was treated with a
þꢄ
[M
] (5), 159 (72), 117 (21), 104 (34), 91 (100), 81 (19),
8 (25), 55 (32). HRMS (EI) for C H I: calcd 286.0218; found
7
12 15
2
86.0215.
(4-Phenylcyclohexyl)azide (3)
Di-tert-butylhyponitrite (5 mg, 3 mol-%) was added every 2 h to
a refluxing mixture of cis-(4-iodocyclohexyl)benzene (286 mg,
1.0 mmol), pyridinesulfonyl azide (550 mg, 3.0 mmol) and
Bu Sn (0.76 mL, 1.5 mmol) in dry benzene under N . Upon
saturated aqueous NaHCO solution (slow addition) and the
3
organic layer was removed. The aqueous layer was extracted
with benzene (2 ꢀ 3.3 mL). The combined organic layers
afforded a 0.5 M benzene solution of trifluoromethanesulfonyl
azide in benzene (determined using hexafluorobenzene as an
internal F NMR standard). C NMR ([D6]benzene, 75 MHz)
1
d 119.6 (q, J ¼ 320 Hz). F NMR (400 MHz, CDCl ) d ꢁ76.2.
6
2
2
completion of the reaction, the crude product was purified by
column chromatography (pentane) using silica gel containing
10 % of KF to afford 3 as a cis/trans 3 : 1 mixture of diaster-
1
9
13
9
1
eomers (149 mg, 74 %) as a colourless oil. trans-3: H NMR
(300 MHz, CDCl ) d 7.37–7.17 (m, 5H), 3.99–3.94 (m, 1H),
3
3
2
.60–2.45 (m, 1H), 2.04–1.93 (m, 2H), 1.89–1.62 (m, 6H).
C NMR (75 MHz, CDCl ) 146.8, 128.4, 126.8, 126.1, 57.1,
3
4
-Phenylcyclohexan-1-ol
1
3
To a solution of LiAlH (0.95 g, 25 mmol) in Et O (25 mL) was
4
2
43.5, 30.0, 28.3. IR (neat) n ¼ 2925, 2857, 2090, 1492, 1446,
added 4-phenylcylohexanone (4.36 g, 25 mmol) in Et O
2
(40 mL). The reaction mixture was stirred for 2 h before being
diluted with Et O and cooled to 08C in an ice bath. Water was
ꢁ1 þꢄ
1255, 754, 697 cm . MS (EI) m/z (%) 201 [M ] (0.1), 172
31), 144 (51), 130 (63), 117 (79), 91 (100), 77 (26), 56 (22).
HRMS (EI) for C H N : calcd 201.1266; found 201.1264.
(
2
1
2 15 3
slowly added followed by 15 w/v % aqueous NaOH solution and
H O. The resulting solution was allowed to warm up to room
2
Determination of the Response Factor R for GC Analysis
F
temperature and stirring was continued for 15 min. The pre-
cipitate was filtered off and the aqueous layer was further
extracted with Et O. The combined organic layers were dried
GC analysis: Column Optima d3 (Macherey-Nagel), l ¼ 30 m,
ꢁ
1
0–2808C, rate 48C min , constant pressure 85 kPa, helium.
4
2
tR (2) ¼ 11.87 min, tR (cis-3) ¼ 19.65 min, tR (trans-3) ¼
(Na SO ) and the solvent was removed under reduced pressure.
2 4
1
9.07 min.
Determination of the 3/2 ratios was made according to Eqn 4:
The crude product was purified by flash chromatography
pentane/Et O, 1 : 1 to 1 : 2) to afford the trans (3.42 g, 78 %) and
cis (0.35 g, 8 %) alcohols, both as white crystals. trans-4-
(
2
3
2
A3
1
1
Phenylcyclohexan-1-ol: white crystals; mp: 118.68C. H NMR
(300 MHz, CDCl ) d 7.33–7.18 (m, 5H), 3.79–3.67 (m, 1H),
¼
ꢀ
ð4Þ
A2 RF
3
2
(
.52 (tt, J ¼ 11.7, 3.4 Hz, 1H), 2.17–2.08 (m, 2H), 2.01–1.92
3
A , A : peak area for compound 2 and 3, respectively. R is the
F
1
3
m, 2H), 1.64–1.38 (m, 4H). C NMR (75 MHz, CDCl ) 146.5,
2
3
response factor between B and A.
The response factor R was determined according to Eqn 6 by
1
2
28.4, 126.8, 126.1, 70.7, 43.4, 36.0, 32.4. IR (neat) n ¼ 3422,
ꢁ
1
921, 2851, 1601, 1494, 1452, 1060 cm . MS (EI) m/z (%) 176
F
injecting three different solutions containing pure 2 and 3 in
equal concentration and measuring the peak area ratios A /A .
Authentic 3 was used as a mixture of diastereoisomers. A mean
þ
[
9
M ] (4), 158 (100), 143 (69), 130 (55), 117 (39), 104 (72),
1 (56), 78 (22), 65 (12). HRMS (EI) for C H O: calcd
12 16
3
2
1
crystals; mp: 71.98C. H NMR (300 MHz, CDCl ) d 7.33–7.14
76.1201; found 176.1201. cis-4-Phenylcyclohexan-1-ol: white
1
of three measurements gave a R ¼ 1.08. The ratio 3/2 for the
F
3
experiments at different concentrations were determined by Eqn
5
(
(
m, 5H), 4.12 (s, 1H), 2.53 (tt, J ¼ 11.6, 2.8 Hz, 1H), 1.99–1.82
from A and A :
3 2
1
m, 4H), 1.74–1.60 (m, 4H), 1.53 (s, 1H). C NMR (75 MHz,
3
CDCl ) 147.3, 128.3, 126.8, 125.9, 65.5, 43.8, 33.0, 27.7. The
3
A3 n2
ꢀ
1
13
H and C NMR spectra are in agreement with literature
RF ¼
ð5Þ
A2 n3
[
25]
data.
n , n : number of moles of 2 and 3, respectively. When
2
3
cis-(4-Phenylcyclohexyl)iodide (1)
equimolar amounts of 2 and 3 are used, Eqn 5 becomes:
To a solution of triphenylphosphine (1.74 g, 6.64 mmol) in
CH Cl (15 mL) was added imidazole (452 mg, 6.64 mmol) and
A3
RF ¼
A2
2
2
ð6Þ
iodine (1.68 g, 6.64 mmol). The mixture was stirred for 10 min
before trans-4-phenylcyclohexanol (780 mg, 4.42 mmol) in
CH Cl (15 mL) was added and the solution was stirred over-
Competition Reaction between (TMS) SiH and PySO N
3
2
3
2
2
night at room temperature. The resulting mixture was diluted
with CH Cl and washed with a 20 w/v % aqueous solution of
Na S O . The organic phase was dried over MgSO , filtered,
A stock solution of PySO N (260 mg) in benzene (5 mL) was
2 3
2
2
prepared and aliquots of 0.1, 0.2, 0.3, 0.4, and 0.6 mL were
transferred to 10 mL round bottom flasks. A stock solution of
(TMS) SiH (373 mg) in benzene (5 mL) was made up and
2
2
3
4
and then concentrated under reduced pressure. The crude
product was purified by flash chromatography (pentane) to give
cis-(4-phenylcyclohexyl)iodide 1 (796 mg, 63 %). White crys-
3
0.5 mL added to each flask, followed by (4-phenylcyclohexyl)
iodide (0.5 mL of a 0.03 M solution in benzene). Each flask
was then filled up to 4.5 mL with benzene before di-tert-
butylhyponitrite (1 mg) was added and the resulting mixture was
placed in a preheated oil bath at 808C for 1 h. A few drops of the
1
tals. Mp: 68.38C. H NMR (300 MHz, CDCl ) d 7.30–7.08
3
(
(
m, 5H), 4.85 (s, 1H), 2.50 (tt, J ¼ 11.9, 3.5 Hz, 1H), 2.18–1.88
1
m, 4H), 1.74–1.55 (m, 4H). C NMR (75 MHz, CDCl ) 146.7,
3
3

Radical Azidation with Sulfonyl Azides
345
Table 1. Competition experiments between (TMS)
3
SiH and PySO
2
N
3
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[
[
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3/2
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CF SO
3
2
N
3
OL702832X
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[
[
2
011, 133, 13890. doi:10.1021/JA2054989
CF
3
2
SO N
3
[mM]
(TMS)
3
SiH [mM]
3/2
8] J. Waser, E. M. Carreira, in Organic Azides: Syntheses and Applica-
tions (Eds S. Br a¨ se, K. Banert) 2010, pp. 95–111 (Wiley: Chichester).
1
2
3
4
1
2
3
4
42
42
42
42
0.868
1.333
2.175
2.370
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ANIE3460.3.0.CO;2-6
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reaction mixture were filtered through a small pad of silica gel in
a Pasteur pipette and eluted with Et O. The 3/2 product ratios
[
[
2
1
7511. doi:10.1021/JA1068036
13] P. Panchaud, C. Ollivier, P. Renaud, S. Zigmantas, J. Org. Chem.
004, 69, 2755. doi:10.1021/JO035843Y
were determined by GC analysis using the response factor
determined with authentic samples of 2 and 3 (Table 1).
A plot of 3/2 as a function of [PySO N ] gave a slope of 16.0
2
2
3
[14] N. Mantrand, P. Renaud, Tetrahedron 2008, 64, 11860. doi:10.1016/
1
(
ꢃ1) Mꢁ
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Ltd: Chichester).
[
Competition Reaction between (TMS) SiH and F CSO N
3
3
3
2
[
A 0.5 M stock solution of CF SO N in benzene (5 mL) was
3
2 3
used, with aliquots of 0.1, 0.2, 0.3, and 0.4 mL transferred to
separate 10 mL round bottom flasks. A stock solution of
(TMS) SiH (373 mg) in benzene (5 mL) was made up and
3
[17] H.-S. Dang, B. P. Roberts, J. Chem. Soc., Perkin Trans. 1 1996, 1493.
0
.5 mL added to each flask, followed by (4-phenylcyclohexyl)
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[
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doi:10.1021/JO060824K
iodide (0.5 mL of a 0.03 M solution in benzene). Each flask was
then filled up to 4.5 mL with benzene before di-tert-
butylhyponitrite (1 mg) was added and the resulting mixture was
placed in a preheated oil bath at 808C for 1 h. A few drops of the
reaction mixture were filtered through a small pad of silica gel in
[
[
[
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AR00016A003
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a Pasteur pipette and eluted with Et O. The 3/2 product ratios
2
were determined by GC analysis using the response factor
determined with authentic samples of 2 and 3 (Table 2).
A plot of 3/2 as a function of [F CSO N ] gave a slope of
[22] P. Panchaud, P. Renaud, Adv. Synth. Catal. 2004, 346, 925.
3
2 3
1
.
4
8 ꢃ 2 Mꢁ
doi:10.1002/ADSC.200404038
[
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Supplementary Material
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1
13
19
H, C, and F NMR spectra of iodide 1, azide 3, PySO N , and
2
3
CF SO N are available on the Journal’s website.
3 2 3
Acknowledgements
The authors thank the Swiss National Science Foundation (Project
0020_135087) for financial support and Guillaume Povie and Giorgio Villa
for insightful suggestions and stimulating discussions.
2