π-Conjugated Triazenes: Intermediates That Undergo Oxidation and Substitution Reactions

Article abstract of DOI:10.1021/acs.joc.6b02705

Novel reactivity for π-conjugated triazenes is herein reported. This observed and unprecedented triazene reactivity gave access to oxidation and substitution reactions. These transformations include successful synthesis of aldehydes, ketones, ethers, and sulfides from readily available organic azides via π-conjugated triazene intermediates. Notably, the afforded adducts were obtained in good yields, at room temperature, and in the absence of added metal catalysts.

Full text of DOI:10.1021/acs.joc.6b02705

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Article
#-Conjugated Triazenes: Intermediates that
Undergo Oxidation and Substitution Reactions
Enrique Barragan, and Alejandro Bugarin
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b02705 • Publication Date (Web): 13 Jan 2017
Downloaded from http://pubs.acs.org on January 13, 2017
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π-Conjugated Triazenes: Intermediates that Undergo Oxida-
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Enrique Barragan and Alejandro Bugarin*
Department of Chemistry and Biochemistry, University of Texas at Arlington, TX 76019, USA
Supporting Information Placeholder
O
I
aldehydes
&
ketones
N
N
2. DMSO
cat. H
Me
Me
R
R1
1. base
THF
N3
Nu
ethers
&
R1 sulfides
2. NuH
cat. H
R
R1
R
*Metal-Free Procedure
*Ambient Reaction Conditions
ABSTRACT: Novel reactivity for π-conjugated triazenes is herein reported. This observed and unprecedented triazene reactivity
gave access to oxidation and substitution reactions. These transformations include successful synthesis of aldehydes, ketones,
ethers, and sulfides from readily available organic azides via π-conjugated triazene intermediates. Notably, the afforded adducts
were obtained in good yields, at room temperature, and in the absence of added metal catalysts.
Identification of these byproducts has led to the current report,
which documents the exceptional reactivity of π-conjugated
INTRODUCTION
Molecules that improve access to synthetic targets, so-called
‘versatile molecules’, have played an important role throughout
the history of chemistry. It is well known that allenylsilanes,1
arylsulfonium salts,2 hypervalent iodine,3 dimethylsulfoxide,4
dimethylformamide,5 and organic azides6 are examples of mol-
ecules that can be derivatized through various pathways. In
addition, their general usefulness reflects the fact that these
molecules can also function as reagents, intermediates, or cata-
lysts for many transformations. Among these versatile mole-
cules, organic azides are perhaps the most widely used com-
pounds as exemplified in: click chemistry,7 syntheses of natural
products,8 heterocycles,9 Staudinger reaction,10 and nitrene
precursors.11 Recently, we observed that π-conjugated tri-
azenes, synthesized from azides and N-heterocyclic carbenes
(NHCs),12 provide potentially valuable new intermediates for
use in organic syntheses.13 Initially, we investigated the ther-
mal stability of these π-conjugated triazenes. It was observed
that these triazenes were stable at 60 ºC for 2 hours. However,
when these same triazenes were heated at 120 ºC some by-
products (unknown at the time) were observed for a couple of
triazenes (e.g., 1).12 Later identification of these byproducts
revealed them to be an iminoimidazole (e.g., 2) and a carbonyl
compound (e.g., 3) (Figure 1).
triazenes, results that now suggest inclusion of these com-
pounds in the list of ‘versatile molecules’. Specifically, this
communication reports an unprecedented simple two-step pro-
tocol that commences from readily available organic azides to
provide syntheses of aldehydes, ketones, ethers, and sulfides
via π-conjugated triazene intermediates. Furthermore, the me-
Table 1. Optimization of Reaction Conditionsa
Ph
Mes
Ph
N
N
O
Mes
Mes
Ph
N
N
N
DMSO
N
N
Ph
Ph
acid (cat.)
N
4
5
6
Ph
Mes
entry
temp (ºC)
120
120
120
120
120
rt
time (h) ratio (5:6)b yield 6 (%)c
acid
1
2
3
4
5
6
7
8
none
none
2
12
2
4:1
4:1
1:1
1:3
1:3
1:4
1:9
1:2
20
21
43
58
62
72
89
39
PdCl2
ZnCl2
2
CuSO4
SnCl4
TsOH
TFA
2
5
rt
0.5
0.5
N
N
Me
Me
rt
N
N
O
Me
Me
Ph
aReactions were carried out with triazene 4 (0.2 mmol, 103 mg, 1.0
equiv.) and the corresponding acid (0.1 mmol, 0.5 equiv.) in 1.0 mL of
DMSO-d6
N
Ph
H
N
N
N
120 ºC, 2 h
1
2
3
1
DMSO. bRatios calculated using H NMR. cIsolated yields (average of
Ph
(4:1)
2-3 runs) by silica gel flash chromatography.
Figure 1. Initial observation.
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thod is compatible with a wide-range of nucleophiles, includ- cond, the TsOH-DMSO catalyzed oxidation, in the second
1
2
3
4
5
6
7
8
ing oxygen, and sulfur nucleophiles, as achieved under mild
reaction conditions. This adds to the previously known reac-
tivity of π-conjugated triazenes: nitrogen extrusion and selec-
tive N-methylation.14
step, is affected by steric effects of the triazene intermediate
(e.g., 8b is more steric hindered than 8a). This size difference
makes 8b more stable, therefore less responsive to Brønsted
acid activation. In contrast, 8a produces a less steric hindered
or more reactive triazene intermediate, which afforded benzo-
phenone 6 in 72% yield after two-step one-pot reaction versus
a 60% yield using 8b. Thus, these results establish 1,3-
dimethylimidazolium iodide 8a as the best NHC precursor,
among those tested, to accomplish this unprecedented trans-
formation. Furthermore, azide 7, alcohol 9, and alkyl bromide
10 counterparts, were reacted under the same reaction condi-
tions, with or without the Brønsted acid, and no reaction was
observed for any of the substrates at rt. This indicating the acti-
vation is due to the triazene (Table 2, bottom).15
RESULTS AND DISCUSSION
To help optimize reaction conditions, triazene 4 was synthe-
sized (Table 1). This selection was based on the consideration
that triazene 4 produces benzophenone 6, instead of the volatile
benzaldehyde 3, thus easing isolation. Heating of triazene 4 at
120 ºC for 2 hours in DMSO, without any additive, afforded
benzophenone 6 in 20% yield (entry 1). Increasing the reaction
time did not improve the reaction yield (entry 2), indicating
that the triazene is the reacting substrate and not the iminoim-
idazole by-product 5, which remains intact after 12 hours of
heating. Based on this observation, to activate further triazene
4, we screened several Lewis and Brønsted acids (entries 3-8)
and it was clearly established that the stronger the Lewis acid,
the higher the yield. In fact, SnCl4 furnished the product in
72% yield even at room temperature (entry 6). Nonetheless,
among all screened Lewis and Brønsted acids, TsOH afforded
the product with the highest yield (89%) at room temperature,
as achieved in only 30 min. (entry 7). Based on this result, we
decided to use TsOH for further investigations.
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Table 3. Scope of the Oxidation Reactiona
N3
O
1.KOt-Bu, THF
I
N
N
O
Me
Me
R1
R2
2. TsOH, DMSO
R1
R2
12a-j & 6
11a-j & 7
8a
O
O
O
H
H
H
H
MeO
O
O2N
Cl
Table 2. Optimization of NHC Precursorsa
12a
12b
12c
23%c
O
12d
12%c
44%b
60%b
N3
O
1. KOt-Bu, THF, rt
X
Y
N
R1
R2
O
O
Ph
Ph
2. TsOH, DMSO, rt
Ph
Ph
7
8a-e
6
H
O
H
H
Ph
Me
S
NC
N
N
N
N
N
N
t-Bu
Mes
t-Bu
Me
Me
Mes
12e
29%c
12f
traces
12g
12h
60%b
O
0%
Cl
BF4
I
O
8a, 72%b
8b, 60%b
8c, traces
Me
H
H
Ph
Ph
72%c
N
N
N
Mes
Mes
12i
43%c
12j
6
I
0% 1-gram scale: 67%d
8d, 5%b
8e, traces
Cl
S
aReactions were carried out with dimethylimidazolium iodide 8a (0.75
mmol, 168 mg, 1.5 equiv.), KOt-Bu (0.75 mmol, 84 mg, 1.5 equiv.), and
the corresponding azide 11a-i & 7 (0.5 mmol, 1.0 equiv.) in 1.0 mL of
THF for 12 h. The volatiles were then removed under reduced pressure.
This was followed by addition of 1.0 mL of DMSO and TsOH (0.25 mmol,
N3
Br
OH
O
DMSO
or
or
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
No reaction with
or without TsOH
b
1
48 mg, 0.5 equiv.) and stirred at rt for 30 min. Yields calculated using H
7
9
10
6
NMR with DMF as internal standard. cIsolated yields (average of 2-3 runs)
d
by silica gel flash chromatography. Isolated yield for 1-gram scale reac-
aReactions were carried out with benzhydryl azide 7 (0.2 mmol, 42 mg, 1.0
equiv.) the corresponding NHC precursor 8a-e (0.3 mmol, 1.5 equiv.),
KOt-Bu (0.3 mmol, 34 mg, 1.5 equiv.), in 1.0 mL of THF for 12 h. Then,
the volatiles were removed under reduced pressure. Followed by addition
of 1.0 mL of DMSO and TsOH (0.1 mmol, 17 mg, 0.5 equiv.) and stirred
at rt for 30 min. b Isolated yields (average of 2-3 runs) by silica gel flash
chromatography.
tion.
With the optimal conditions for the two-step one-pot procedure
in hand, we subsequently explored the scope of this new trans-
formation (Table 3) by surveying the reactivity of freshly pre-
pared organic azides (11a-j & 7) and 1,3-dimethylimida-
zolium iodide 8a using KOt-Bu and THF, at room temperature.
All reactions were terminated after 12 h (the standard time for
triazene formation) for comparison purposes, although starting
materials were still present. THF was then removed under re-
duced pressure and a catalytic amount of TsOH (50 mol%) in
DMSO was added to the reaction mixture. The reaction mix-
ture was quenched after only 30 min. and the product was iso-
lated using silica gel flash chromatography. From this study, it
was observed that secondary azides afford their products in
higher yields (e.g., 6 and 12h were obtained in 72% and 60%
yield, respectively). The system is also efficient for the allylic
Having optimized conditions for the conversion of a π-
conjugated triazene to a carbonyl compound, we next investi-
gated the scope of converting benzhydryl azide 7 to benzophe-
none 6 in a two-step one-pot protocol (Table 2), this to demon-
strate a net conversion of organic azides into carbonyl com-
pounds via a triazene intermediate. Examining the new reactiv-
ity, in a two-step one-pot procedure, presented two challenges.
First, the formation of the triazene intermediate is dependent of
the NHC precursor used (e.g., 8c, 8d, and 8e did not provide a
significant yield of their respective triazene intermediate). Se-
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azide 11i, affording trans-cinnamaldehyde 12i in moderate triazenes 1, 13, and 14 and subjected them to reaction condi-
1
2
3
4
5
6
7
8
yield (43%). Two classes of primary azides were investigated;
benzylic azides and aliphatic azides. Unfortunately, aliphatic
azides proved to be unreactive towards our reaction conditions
and did not create the expected aldehydes products (e.g., 12g
and 12j). Nonetheless, the other class of primary azides (ben-
zylic) exhibited high sensitivity to electronic effects. The elec-
tron-rich 4-methoxy-benzaldehyde 12b was obtained in a good
yield (60%), whereas benzaldehyde 12c was obtained in a
moderate yield (44%), and the electron-poor 4-
nitrobenzaldehyde 12c was obtained in relatively small yield
(23%). Finally, several heterocycles containing a benzylic az-
ide were investigated (not shown), including 2-(azidomethyl)-
thiophene 11f, but unfortunately only traces of thiophene-2-
carbaldehyde 12f were observed. This presumably indicates
Brønsted acid protonation of the heterocycle itself, instead of
activation of a nitrogen atom on the triazene moiety, leading to
unknown decomposition pathways. Overall, although the yields
are modest, it is worth noting that this is a two-step one-pot
procedure and represents the net conversion of an azide to a
carbonyl compound under mild reaction conditions, in other
words, an unprecedented transformation.
tions described in Table 4, in the presence of oxygen and sulfur
nucleophiles. Since DMSO cannot longer be the reaction’s
solvent, a brief solvent screening was performed using catalytic
TsOH and 50 equiv. of methanol as nucleophile. Unfortunate-
ly, low yields were observed with other solvents (e.g., DMF,
acetone, THF, EtOAc, and CH2Cl2). However, very surprising-
ly, when investigating thiophenol as nucleophile, we observed
an excellent yield (96%) of sulfide 15f, without an external
Brønsted acid (Table 4). This result indicates that thiophenol
can serve as both nucleophile and Brønsted acid. In addition,
two more sulfides derivated from thiophenol were also synthe-
sized and afforded the desired products 15d and 15e in 54%
and 40% yield, respectively (Table 4). To our gratification,
using 4-bromothiophenol as nucleophile in THF also afforded
the sulfide adducts 15g (from 14), 15h (from 13), and 15i
(from 1) in 29%, 33%, and 53% yield, respectively.
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Encouraged by these results, and because ethers and their cor-
responding derivatives are valuable synthetic intermediates,18
we next explored the compatibility of the thiophenol-mediated
nucleophilic substitution using oxygen containing nucleophiles.
We were pleased to discover that our approach is viable for use
with nucleophiles other than thiols. For example, good results
were obtained with methanol and ethanol, using only 5-mol%
of thiophenol as Brønsted acid. Triazene 14, afforded ethers
15a and 15b in 51% and 48% yield, respectively, while tri-
azene 1 gave benzylmethyl ether 15c in 20% yield. The low
yield of 15c is apparently due to the higher activation energy
required to liberate its benzyl carbocation intermediate (Table
4).
Scheme 1. Proposed Mechanism (acidic conditions)
N
N
N
H
N
N
N
Me
Me
Ph
Me
Me
Me
Ph
Me
14b
HA
N
N
NH
N
N
N
N
SN1
Ph
Ph
14
N2
Ph
14a
Ph
Table 4. Scope of Substitution Reactions
SN
2
14c
Me
R
Kornblum type
mechanism
Ph
Me
S
O
Nu
O
N
O & S Nucleophiles
N
Ph
S
N
N
Ph
O
Me
Ph
Ph
Me
Ph
R
Me
N
1, R = H
13, R = Me
14, R = Ph
cat. H
14f
Me
14e
14d
S
Triazenes
Me
6
15a-j
OMe
Me
Oxygen nucleophilesa
OMe
OEt
Ph
In order to elucidate further the mechanistic details of this nov-
el transformation, we turned our attention to the data obtained
during the azide survey (Table 3), the reagents employed
(TsOH and DMSO), and the detection of dimethyl sulfide 14f
as a byproduct. From Table 2, it is clear that secondary azides
are the best substrates, followed by allylic azides, benzylic
azides, and finally primary aliphatic azides (which do not
work). Based on this information, we propose a SN1 mecha-
nism where triazene 14 is first activated by TsOH, followed by
fast triazene disintegration into three fragments. These frag-
ments are nitrogen gas (bubbles observed), iminoimidazole 14b
and carbocation 14c. After carbocation 14c is released, DMSO
quickly traps it, forming the alkoxysulfonium intermediate 14e.
Finally, 14e undergoes a Kornblum type mechanism,16,17 which
release dimethyl sulfide 14f (observed) and the expected ben-
zophenone 6. An alternative, less likely, mechanism is the di-
rect attack of DMSO to protonated triazene 14a (SN2). Howev-
er, the data from Table 2 suggest that substrates that produce
more stable carbocations (secondary azides) generated higher
yields, supporting the proposed SN1 mechanism (Scheme 1).
Ph
Ph
Ph
Ph
15a, 51%e
15b, 48%e
15c, 20%e
Sulfur nucleophilesb,c
SPh
SPh
SPh
1-gram scale:
Ph
Ph
15d, 54%e
Br
Ph
Me
Ph
15f, 96%e
Br
15f, 72%f
15e, 40%e
Br
S
S
S
Ph
Me
15h, 33%e
Ph
Ph
Me
Ph
Ph
15g, 29%e
Synthesis of Benadryl®d
15i, 53%e
15j, 35%e
N
Ph
O
Me
Diphenhydramine (Benadryl®)
aReactions were carried out with triazene 1 or 14 (0.3 mmol, 1.0 equiv.),
and 5% PhSH in 0.5 mL of the corresponding alcohol (methanol or etha-
nol) at 55 °C for 4 h. bReactions were carried out with its respective tri-
azene 1, 13, or 14 (0.3 mmol, 1.0 equiv.) in 0.3 mL of thiophenol at rt for 1
h. Reactions were carried out with its respective triazene 1, 13, or 14 (0.3
mmol, 1.0 equiv.), and 4-bromothiophenol (0.6 mmol, 76 mg, 2.0 equiv.)
Considering the proposed Scheme 1 mechanism, it was hy-
pothesized that nucleophiles, other than DMSO, could attack
the protonated triazene intermediate 14a. If so, this would al-
low access to a variety of organic compounds from common
triazene intermediates. To test this hypothesis, we synthesized
c
d
in 0.5 mL of THF at rt for 1 h. Reaction was carried out with triazene 14
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(0.3 mmol, 92 mg, 1.0 equiv.) and TsOH (0.15 mmol, 29 mg, 0.5 equiv.) in
this reaction, a comprehensive set of experiments was per-
formed as follows: Triazene 14 was subjected to an excess of
e
0.5 mL of dimethylaminoethanol at 60 °C for 36 h. Isolated yields (aver-
1
f
age of 2-3 runs) by silica gel flash chromatography. Isolated yield for 1-
2
3
4
5
6
7
8
9
different bases (20.0 equiv.) and stirred at room temperature
for 3 h. From this study, it was found that organic bases such as
DBU did not promote this oxidation (entry 2). On the other
hand, CsCO3, KOt-Bu, and NaH provided the adduct 6 in 55%,
56%, and 58% yield, respectively (entries 3 to 5). Since these
reactions were performed under an air atmosphere and oxygen
is known to promote alcohol oxidations under basic condi-
tions,25 we carried out an oxygen-free reaction by purging THF
with Argon and stirring the reaction mixture under an Argon
atmosphere (entry 6). Surprisingly, the yield was comparable
under both Argon (57%) vs air (58%), and absence of base did
not produce benzophenone 6 (entry 1).
gram scale reaction.
To further demonstrate the synthetic utility and practicality of
this transformation, we applied our methodology to the synthe-
sis of the antihistaminic drug diphenhydramine (15j, Bena-
dryl®),19 depicted on the bottom of Table 4. The synthesis of
15j was accomplished using triazene 14 and 2-
(dimethylamino)ethanol, as nucleophile, at 60 ºC for 36 h, with
a modest 35% yield. The lower yield obtained in this case is
the result of incomplete reaction due to the nature of the start-
ing material (very polar oxygen nucleophile); extended reac-
tion times will likely provide increased yields.
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12
13
14
15
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Overall, the data in Tables 3 & 4 provide strong certification
for the unusually wide scope inherent in our approach. These
preliminary results clearly establish that this method can be
used to prepare selectively substituted ketones and aldehydes,
structural motifs present in a plethora of important compounds
as illustrated with the above noted synthesis of the ether con-
taining drug [Benadryl®]. The notable feature of our new car-
bonyl synthesis is the use of acidic conditions to accomplish
the oxidation (Scheme 1), instead of the well-known basic
conditions used for the reported DMSO oxidations (e.g., Korn-
blum16,17 and Swern20,21,22). This method thus enables the syn-
thesis of ketones and aldehydes from azides under acidic me-
dia, a current limitation of the Kornblum and Swern oxida-
tions.23,24
Subsequently, we performed a two-step, one-pot procedure,
without the isolation of triazene 14 from NHC precursor 8a and
benzhydryl azide 7, under basic conditions (entry 7). This also
provided benzophenone 6 in similar yield (50%), supporting
the power of using a one-pot procedure. Finally, to eliminate
the possible background reaction during the in situ formation
of triazene 14, benzhydryl azide 7 was also subjected to 20
equiv. of sodium hydride, in both air and argon atmosphere,
resulting in no reaction, as expected (Table 5, entries 8 and 9),
indicating that triazene 14 is the reactive specie.
In an effort to extend the scope of this transformation using
basic conditions, all azide-precursors of aldehydes and ketones
from Table 3 were screened. Unfortunately, only benzophe-
none 6 was observed in 50% yield (Table 5, entry 7) and 4-
cyanobenzaldehyde 12e in less than 10% yield. We propose
that product formation, under basic conditions, undergoes a
polar mechanism (Scheme 2). First, a benzylic deprotona-
tion takes place to form triazene anion 14a’, followed by a
selective protonation to form intermediate 14b’. Thereafter,
14b’ decomposes to NHC 14c’ and imine 14d’ (observed),
with nitrogen extrusion providing the driving force. Finally,
hydrolysis of the imine produces benzophenone 6. However,
it should be noted, that a radical mechanism is also plausi-
ble. Additional studies are required to either refute or sup-
port this hypothesis.
Table 5. Oxidation Reaction Under Basic Conditionsa
Ph
Me
Ph
O
N
N
N
Base
Ph
Ph
N
THF, rt
N
14
6
Me
entry
base
atmosphere time (h) yield 6 (%)e
substrate
1
2
14
14
none
DBU
CsCO3
KOt-Bu
NaH
Argon
O2/air
O2/air
O2/air
O2/air
Argon
O2/air
Argon
O2/air
3
3
3
3
3
3
3
3
3
0
0
Scheme 2. Proposed Mechanism (basic conditions)
3
14
55
56
58
57
50
0
4
14
5
14
N
N
N
N
Me
Me
Me
Me
H
B
B
6
14
NaH
N
N
7c
8d
9d
8a + 7
7
NaH
H
B
N
N
N
N
NaH
Ph
-B
14
H
14a'
7
NaH
0
Ph
Ph
Ph
aReactions were carried out with triazene 14 (0.3 mmol, 93 mg, 1.0
equiv.) and the corresponding base (6 mmol, 144 mg, 20 equiv.) in THF
OH
Me
N
N
b
N
N
Me
(3 mL) stirring at rt for 3 h. Reactions carried out under Argon atmos-
Me
Me
c
phere. Reactions were carried out with dimethylimidazolium iodide 8a
14c'
N
(0.3 mmol, 67 mg, 1.5 equiv.), KOt-Bu (0.3 mmol, 34 mg, 1.5 equiv.),
and benzhydryl azide 7 (0.2 mmol, 42 mg, 1.0 equiv.) in 1.0 mL of THF
for 12 h. Followed by addition of NaH (4 mmol, 96 mg, 20 equiv.) and
stirring at rt for 3h. dReactions were carried out with benzhydryl azide 7
(0.3 mmol, 63 mg, 1 equiv.) and NaH (6 mmol, 144 mg, 20 equiv.) in
THF (3 mL) stirred at rt for 3h. eIsolated yields (average of 2-3 runs) by
silica gel flash chromatography.
O
14b'
hydrolysis
H2O
N
N
NH
Ph
Ph
Ph
14d'
N2
H
HO
6
Ph
Ph
Ph
In conclusion, we have documented, for the first time, a new
versatile molecule, i.e. π-conjugated triazene, capable of un-
dergoing both oxidation and substitution reactions, under mild
reaction conditions. The transformations described above es-
tablish the use of organic azides as useful synthetic scaffolds
for the synthesis of aldehydes, ketones, ethers, and sulfides
While synthesizing triazene 14 with a small excess of base (1.5
equiv. of KOt-Bu), trace amounts of benzophenone 6 were
observed, indicating that an oxidation of benzhydryl azide 7
was occurring (Table 5). In order to interpret the mechanism of
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products were purified by column chromatography on silica
compounds via π-conjugated triazene intermediates. In general,
1
2
3
4
5
6
7
gel, using hexanes as mobile phase yielding product 11f.
the produced adducts were observed in moderate to excellent
yields, under mild reaction conditions. Also, sulfur nucleo-
philes were better than oxygen nucleophiles. Overall, this un-
precedented methodology not only broadens the application of
traditional organic azides, but it additionally provides direct
disconnections for rapidly building organic frameworks, an
important consideration in many synthetic studies.
(Azidomethylene)dibenzene (7). Known compound.26 Colorless
1
liquid. (146 mg, 70% yield). H NMR (500 MHz, CDCl3) δ
7.46-7.36- (m, 10H), 5.79 (s, 1H); 13C NMR (125 MHz,
CDCl3) δ 139.8, 128.9, 128.3, 127.6, 68.7.
(Azidomethyl)benzene (11a). Known compound.26 Colorless
1
liquid. (109 mg, 82% yield). H NMR (500 MHz, CDCl3) δ
8
9
7.49-7.39 (m, 5H), 4.37 (s, 2H); 13C NMR (125 MHz, CDCl3) δ
EXPERIMENTAL SECTION
135.6, 129.0, 128.5, 128.4, 54.9.
General Information: All reactions were carried out in ov-
en-dried glassware with magnetic stirring. All NHC precursors
were commercially obtained and used as received with the
exception of 8a, which was synthesized using a known proce-
dure.12 Solvents were dried and degassed from a solvent purifi-
cation system. Heating was accomplished by oil bath. Purifica-
tion of reaction products was carried out by flash column
chromatography using silica gel 60 (230-400 mesh). TLC visu-
alization was accompanied with UV light and KMnO4 and
iodine stains. The removal of volatile solvent was accom-
plished using a rotary evaporator attached to a dry diaphragm
pump (10-15 mm Hg) followed by pumping to a constant
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1-(azidomethyl)-4-methoxybenzene (11b). Known compound.26
Colorless liquid. (98 mg, 60% yield). 1H NMR (500 MHz,
CDCl3) δ 7.26 (d, J = 8.6 Hz, 2H), 6.93 (d, J = 8.6 Hz, 2H),
4.26 (s, 2H), 3.80 (s, 3H); 13C NMR (125 MHz, CDCl3) δ
159.8, 129.9, 127.6, 114.3, 55.3, 54.5.
1-(azidomethyl)-4-nitrobenzene (11c). Known compound.27
Colorless liquid. (98 mg, 55% yield). 1H NMR (500 MHz,
CDCl3) δ 8.21 (dd, J = 9.2, 2.3 Hz, 2H), 7.48 (d, J = 8.6 Hz,
2H), 4.49 (s, 2H); 13C NMR (125 MHz, CDCl3) δ 147.8, 142.9,
128.7, 124.1, 53.8.
1-(azidomethyl)-4-chlorobenzene (11d). Known compound.29
1
weight with an oil pump (<300 mTorr). H NMR spectra were
1
Colorless liquid. (144 mg, 86% yield). H NMR (300 MHz,
recorded at 500 MHz and 300 MHz, and are reported relative
to CDCl3 (δ 7.25). 1H NMR coupling constants (J) are reported
in Hertz (Hz) and multiplicities are indicated as follows: s (sin-
glet), d (doublet), t (triplet), m (multiplet). Proton-decoupled
13C NMR spectra were recorded at 125 MHz and 75 MHz and
reported relative to CDCl3 (δ 77) IR experiments were recorded
with neat samples on an instrument fitted with diamond ATR
sample plate. High-resolution (HR) mass spectra were recorded
using an ESI-TOF instrument.
General Procedure for the Synthesis of Azides. Method A.
Following a previously reported procedure,26 the corresponding
halide (1 equiv.) was dissolved in DMF (0.5 M). Sodium azide
(1.2 equiv.) was then added and the resulting mixture was
stirred at 80 °C for 4 h. Then, the mixture was allowed to cool
to room temperature and water was added. Two extractions
were then performed with Et2O, the organic layer was washed
with brine dried over Na2SO4 and evaporated under reduced
pressure to yield products 11a, 11b, 11d, 11e, 11g, 11h, and
11j.
Method B. Following a previously reported procedure,27 p-nitro
benzyl chloride (1 mmol), sodium azide (1.2 mmol) and 30 mL
of DMSO were added to a light-shielded reaction flask. The
mixture was then stirred at room temperature for 1 h. Then, 30
mL of water were added. The mixture was extracted with ethyl
acetate (3 x 15 mL), the organic layer was washed with brine
(2 x 15 mL), dried over Na2SO4, and evaporated under reduced
pressure to yield 11c.
Method C. Following a previously reported procedure,28 to a
vigorously stirred solution of NaI (4 mmol) and furfuryl alco-
hol (2 mmol) in 2 mL of acetonitrile under argon was added
methanesulfonic acid (4 mmol) at room temperature. The reac-
tion mixture was stirred for 15 minutes. Then, anhydrous alu-
minum chloride (0.2 mmol) and sodium azide (6 mmol) were
added and the reaction mixture was heated to reflux and stirred
for 5 h. Then, the mixture was allowed to cool to room temper-
ature and quenched with water. Three extractions were then
performed with Et2O, the organic layer was washed with 10%
sodium sulfate solution, dried over Na2SO4 and evaporated
under reduced pressure to yield crude products. The crude
CDCl3) δ 7.36 (d, J = 8.6 Hz, 2H), 7.25 (d, J = 8.6 Hz, 2H),
4.31 (s, 2H); 13C NMR (75 MHz, CDCl3) δ 134.3, 134.1, 129.7,
129.1, 54.1.
4-(azidomethyl)benzonitrile (11e). Known compound.26 Color-
1
less liquid. (123 mg, 78% yield). H NMR (500 MHz, CDCl3)
δ 7.65 (d, J = 8.6 Hz, 2H), 7.42 (d, J = 8.6 Hz, 2H), 4.43 (s,
2H); 13C NMR (125 MHz, CDCl3) δ 140.9, 132.7, 128.6,
118.6, 112.2, 54.1.
2-(azidomethyl)thiophene (11f). Known compound.28 Colorless
liquid. (60 mg, 43% yield). 1H NMR (500 MHz, CDCl3) δ 7.33
(dd, J = 5.2, 1.2 Hz, 1H), 7.06 (d, J = 3.4 Hz 1H), 7.03-7.01
(m, 1H), 4.49 (s, 2H); 13C NMR (125 MHz, CDCl3) δ 137.4,
127.5, 127.3, 126.6, 49.2.
(Azidomethyl)cyclohexane (11g). Known compound.30 Color-
less liquid. (84 mg, 60% yield). 1H NMR (500 MHz, CDCl3) δ
3.08 (d, J = 6.3 Hz, 2H), 1.76-1.70 (m, 4H), 1.57-1.48 (s, 1H),
1.28-1.09 (m 3H), 0.98-0.90 (m, 2H); 13C NMR (125 MHz,
CDCl3) δ 58.1, 38.1, 30.7, 26.3, 25.8.
2-azidoethylbenzene (11h). Known compound.26 Colorless
1
liquid. (130 mg, 88% yield). H NMR (500 MHz, CDCl3) δ
7.45-7.36 (m, 5H), 4.66 (q, J = 6.9 Hz, 1H), 1.58 (d, J = 6.9
Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 141.1, 128.9, 128.3,
126.6, 61.3, 21.7.
Trans-cinnamyl azide (11i). Known compound.31 To a solution
of allylbenzene in 20 mL of CHCl3, Br2 was added at 0 °C. The
mixture was stirred at 0 °C for 10 min, then the solvent was
evaporated at reduced pressure to afford the crude dibromide
intermediate. This intermediate was dissolved in 20 mL of
DMSO and NaN3 (12 mmol) and DBU (20 mmol) were added.
The resulting mixture was stirred at room temperature for 1 h.
Then water was added and the mixture was extracted with ethyl
acetate (3 x 10 mL), the organic layer was dried over Na2SO4
and the solvent was evaporated at reduced pressure to afford
the crude product. This crude product was purified by column
chromatography using Hexanes/Ethyl acetate (9:1) as mobile
phase to afford compound 11i as a colorless liquid (107 mg,
1
67% yield). H NMR (500 MHz, CDCl3) δ 7.48-7.26 (m, 5H),
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6.65 (d, J = 15.8 Hz, 1H), 6.24 (dt, J = 15.8, 6.8 Hz, 1H), 3.94
(d, J = 6.3 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 136.1,
134.7, 128.8, 128.3, 126.8, 122.5, 53.1.
(3-azidopropyl)benzene (11j). Known compound.30 Colorless
liquid (137 mg, 85% yield). 1H NMR (500 MHz, CDCl3)
δ 7.40-7.26 (m, 5H), 3.34 (t, J = 6.9 Hz, 2H), 2.78 (t, J = 7.8
Hz, 2H), 1.98 (dt, J = 7.5, 6.9 Hz, 2H); 13C NMR (125 MHz,
CDCl3) δ 141.1, 128.7, 128.6, 126.3, 50.8, 32.9, 30.6.
room temperature for 12 h. The volatiles were then removed
1
2
3
4
5
6
7
8
under reduced pressure. This was followed by addition of
DMSO (1.0 mL) and TsOH (0.25 mmol) and stirred at room
temperature for 30 min. The crude mixture was then purified
using column chromatography with silica gel and Hex-
anes/Ethyl acetate (9:1) as mobile phase to afford products 6
and 12a-i.
Benzophenone (6). Known compound.32 Colorless liquid. (66
1
mg, 72% yield). H NMR (300 MHz, CDCl3) δ 7.81-7.78 (m,
General Procedure for the Synthesis of Triazenes. Follow-
ing our previously reported procedure,12 to a suspension of the
corresponding NHC precursor (1.5 mmol) in THF (20 mL) was
added the respective azide (1 mmol) and left stirring for 5 min.
KOt-Bu (1.5 mmol) was added to the mixture and left stirring a
room temperature for 12 h. To the resulting mixture 5 mL of
hexanes were added and the solids were filtered through Celite.
The volatiles were evaporated under reduced pressure to afford
an oily product. This crude product was washed with hexanes
(3 x 20 mL) and dried under reduce pressure, which afforded
solid products 1, 4, 13, and 14.
4H), 7.59-7.54 (m, 2H), 7.49-7.43 (m, 4H); 13C NMR (75
MHz, CDCl3) δ 196.8, 137.7, 132.6, 130.2, 128.4. 1-Gram
scale: (547 mg, 67% yield).
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Benzaldehyde (12a). Known compound.33 Colorless liquid. (23
1
mg, 44% yield). H NMR (300 MHz, CDCl3) δ 9.82 (s, 1H),
7.71-7.67 (m, 2H), 7.45-7.25 (m, 3H); 13C NMR (75 MHz,
CDCl3) δ 192.5, 136.4, 134.5, 129.7, 129.0.
4-methoxybenzaldehyde (12b). Known compound.34 Colorless
liquid. (41 mg, 60% yield). 1H NMR (300 MHz, CDCl3) δ 9.78
(s, 1H), 7.74 (d, J = 8.9 Hz, 2H), 6.91 (d, J = 8.9 Hz, 2H), 3.79
(s, 3H); 13C NMR (75 MHz, CDCl3) δ 190.9, 164.7, 132.0,
130.0, 114.4, 55.6.
4-nitrobenzaldehyde (12c). Known compound.34 Pale yellow
solid. (17 mg, 23% yield). 1H NMR (300 MHz, CDCl3) δ 10.13
(s, 1H), 8.34 (d, J = 8. 6 Hz, 2H), 8.05 (d, J = 8.6 Hz, 2H); 13C
NMR (75 MHz, CDCl3) δ 190.6, 151.2, 140.1, 130.6, 124.4.
(E)-1-benzyl-3-(1,3-dimethylimidazol-2-ylidene)triazene (1).
Known compound.12 Strong orange solid. (211 mg, 92% yield).
1H NMR (500 MHz, CDCl3) δ 7.34 (d, J =7.4 Hz, 2H), 7.28 (t,
J = 7.6 Hz, 2H) 7.20 (t, J =7.4 Hz, 1H), 6.30 (s, 2H), 4.83 (s,
2H), 3.52 (s, 6H); 13C NMR (125 MHz, CDCl3) δ 152.7, 139.1,
129.0, 128.2, 126.6, 115.7, 65.3, 35.5.
4-chlorobenzaldehyde (12d). Known compound.34 White solid.
(8 mg, 12% yield). 1H NMR (300 MHz, CDCl3) δ 9.80 (s, 1H),
7.63 (d, J = 8.6 Hz, 2H), 7.29 (d, J = 8.3 Hz, 2H); 13C NMR
(75 MHz, CDCl3) δ 190.8, 140.6, 134.7, 130.8, 129.3.
(E)-1-benzhydryl-3-(1,3-dimesitylimidazol-2-ylidene)triazene
(4). Pale orange solid. (370 mg, 72% yield). IR (neat) ν 3173,
1541, 1489, 1409, 1232, 698 cm-1; 1H NMR (300 MHz, CDCl3)
δ 7.20-7.05 (m, 10 H), 6.87 (s, 4 H), 6.44 (s, 2 H), 4.64 (s, 1
H), 2.31 (s, 6 H), 2.11 (s, 12 H); 13C NMR (75 MHz, CDCl3) δ
152.5, 143.3, 138.3, 135.6, 134.5, 128.9, 128.3, 127.9, 126.3,
116.2, 21.2, 18.2; HRMS (ESI) m/z 514.2965, calcd for
C34H36N5 [M+H]+ 514.2963.
4-formylbenzonitrile (12e). Known compound.35 White solid.
1
(19 mg, 29% yield). H NMR (300 MHz, CDCl3) δ 10.05 (s,
1H), 7.96 (d, J = 8.3 Hz, 2H), 7.81 (d, J = 8.3 Hz, 2H); 13C
NMR (75 MHz, CDCl3) δ 190.9, 138.8, 133.0, 130.0, 117.9,
117.6.
(E)-1-(1-phenylethyl)-3-(1,3-dimethylimidazol-2-
Acetophenone (12h). Known compound.33 Colorless liquid. (36
mg, 60% yield). 1H NMR (300 MHz, CDCl3) δ 7.86 (d, J = 7.2
Hz, 2H), 7.47-7.45 (m, 1H), 7.37-7.32 (m, 2H), 2.48 (s, 3H);
13C NMR (75 MHz, CDCl3) δ 198.0, 137.1, 133.1, 128.6,
128.3, 26.6.
Trans-cinnamaldehyde (12i). Known compound.36 Yellow oil.
(28 mg, 43% yield). 1H NMR (500 MHz, CDCl3) δ 9.60 (d, J =
7.9 Hz, 1H), 7.47-7.44 (m, 2H), 7.38-7.30 (m, 4H), 6.64-6.57
(m, 1H); 13C NMR (125 MHz, CDCl3) δ 193.8, 152.9, 134.1,
131.4, 129.2, 128.6, 128.5.
ylidene)triazene (13). Brown oil. (124 mg, 51% yield). IR
1
(neat) ν 3114, 1660, 1559, 1502, 1418, 1243, 701 cm-1; H
NMR (300 MHz, CD3OD) δ 7.33-7.24 (m, 4H), 7.19-7.16 (m,
1H), 6.62 (s, 2H) 4.69 (q, J = 6.9 Hz, 1H), 3.46 (s, 6H) 1.53 (d,
J = 6.9 Hz, 3H); 13C NMR (75 MHz, CD3OD): δ 152.2, 144.4,
128.0, 127.0, 126.5, 116.4, 68.1, 34.4, 20.7; HRMS (ESI) m/z
244.1550, calcd for C13H18N5 [M+H]+ 244.1555.
(E)-1-benzhydryl-3-(1,3-dimethylimidazol-2-ylidene)triazene
(14). Orange solid. (168 mg, 55% yield). IR (neat) ν 3119,
1
2099, 1555, 1492, 1403, 1260, 694 cm-1; H NMR (300 MHz,
CDCl3) δ 7.39 (d, J = 7.2 Hz, 4H), 7.30-7.20 (m, 4H), 7.19-
7.11 (m, 2H), 6.24 (s, 2H), 5.76 (s, 1H), 3.45 (s, 6H); 13C NMR
(75 MHz, CDCl3): δ 152.8, 143.6, 128.5, 128.3, 126.6, 115.9,
35.6; HRMS (ESI) m/z 306.1713, calcd for C18H20N5 [M+H]+
306.1708.
General Procedure for the Synthesis of Ethers. The corre-
sponding triazene (0.3 mmol) was dissolved in 0.5 mL of the
respective alcohol (methanol for 15a and 15c or ethanol for
15b) and PhSH (0.015 mmol) was added and the mixture was
stirred at 55 °C for 4 h. The volatiles were then removed under
reduced pressure and the crude mixture was purified using
column chromatography with silica gel and Hexanes/Ethyl
acetate (9:1) as mobile phase to afford products 15a-c.
N-benzyl-1,3-dimethyl-1,3-dihydro-2H-imidazol-2-imine (2):
1H NMR (500 MHz, DMSO-d6): δ 7.28-7.27 (m, 4 H, Ph-H),
7.20-7.18 (m, 1 H, Ph-H), 6.52 (s, 2 H, NCH), 4.45 (s, 2 H, Ph-
CH2), 3.15 (s, 6 H, N-CH3). HRMS (ESI, N2): m/z calcd for
C12H15N3 [M + H]+ 202.1339, found 202.1328.
(Methoxymethylene)dibenzene (15a). Known compound.37
Colorless oil. (30 mg, 51% yield). 1H NMR (300 MHz, CDCl3)
δ 7.43-7.29 (m, 10H), 5.30 (s, 1H), 3.44 (s, 3H); 13C NMR (75
MHz, CDCl3) δ 142.2, 128.6, 127.6, 127.1, 85.6, 57.2.
General Procedure for Oxidation Reactions. Dimethylimid-
azolium iodide (0.75 mmol,) and KOt-Bu (0.75 mmol) were
suspended in THF (1.0 mL) and stirred under argon at room
temperature for 15 min. To this suspension the corresponding
azide was added (0.5 mmol) and the suspension was stirred at
(Ethoxymethylene)dibenzene (15b). Known compound.38 Col-
1
orless oil. (31 mg, 48% yield). H NMR (300 MHz, CDCl3) δ
7.43-7.28 (m, 10H), 5.41 (s, 1H), 3.57 (q, J = 6.9 Hz, 2H) 1.32
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(t, J = 6.9 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 142.7, Hz, 2H), 4.09 (s, 2H); 13C NMR (75 MHz, CDCl3) δ 137.1,
1
2
3
4
5
6
7
8
128.5, 127.5, 127.1, 83.6, 64.7, 15.5.
135.5, 132.0, 131.6, 128.9, 128.7, 127.4, 120.4, 39.2.
(Methoxymethylene)benzene (15c). Known compound.39 Color-
Diphenhydramine (15j). Triazene 14 (0.3 mmol) and TsOH
(0.15 mmol) were dissolved in dimethylaminoethanol (0.5 mL)
and stirred at 60 °C for 36 h. The crude mixture was then puri-
fied using column chromatography with silica gel and Ethyl
acetate/Methanol (9:1) as mobile phase to afford product 15j as
colorless oil. (27 mg, 35% yield). IR (neat) ν 3061, 2941, 1492,
1452, 1102, 696 cm-1; 1H NMR (300 MHz, CDCl3) δ 7.46-7.28
(m, 10H), 5.46 (s, 1H), 3.67 (t, J = 5.8 Hz, 2H), 2.71 (t, J = 5.8
Hz, 2H), 2.37 (s, 6H); 13C NMR (75 MHz, CDCl3) δ 142.4,
128.6, 127.6, 127.2, 84.2, 67.6, 59.1, 46.2; HRMS (ESI) m/z
256.1696, calcd for C17H22NO [M+H]+ 256.1700.
1
less oil. (7 mg, 20% yield). H NMR (300 MHz, CDCl3) δ
7.40-7.32 (m, 5H), 4.50 (s, 2H), 3.43 (s, 3H); 13C NMR (75
MHz, CDCl3) δ 138.4, 128.6, 127.9, 127.8, 74.8, 58.2.
General Procedure for the Synthesis of Thiophenol Deriva-
tives. The respective triazene (0.3 mmol) was dissolved in thi-
ophenol (0.3 mL) and stirred at room temperature for 1 h. Then
ethyl acetate (15 mL) was added to the mixture, which was
then washed with 10% NaOH solution (3 x 10 mL). The organ-
ic layer was dried over Na2SO4 and the volatiles were removed
under reduced pressure. The crude mixture was then purified
using column chromatography with silica gel and Hex-
anes/Dichloromethane (1:1) as mobile phase to afford products
15d-f.
Benzhydryl(phenyl)sulfane (15d). Known compound.40 White
solid. (45 mg, 54% yield). 1H NMR (300 MHz, CDCl3) δ 7.44-
7.23 (m, 15H), 5.58 (s, 1H); 13C NMR (75 MHz, CDCl3) δ
141.1, 136.2, 130.6, 128.8, 128.7, 128.5, 127.4, 126.7, 57.5.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
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43
44
45
46
47
48
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60
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS
Publication website at DOI: 10.1021/acs.joc.
1
Additional studies and H and 13C NMR spectra of each
compound (PDF)
Phenyl(1-phenylethyl)sulfane (15e). Pale yellow oil.41 (26 mg,
40% yield). 1H NMR (300 MHz, CDCl3) δ 7.45-7.30 (m, 10H),
4.48 (q, J = 6.9 Hz, 1H), 1.76 (d, J = 6.9 Hz, 3H); 13C NMR
(75 MHz, CDCl3) δ 143.4, 135.4, 132.7, 129.0, 128.7, 127.5,
127.4, 127.3, 48.2, 22.6.
AUTHOR INFORMATION
Corresponding Author
* Email: bugarin@uta.edu.
Benzyl(phenyl)sulfane (15f). Known compound.42 White solid.
Notes
1
The authors declare no competing financial interest.
(58 mg, 96% yield). H NMR (300 MHz, CDCl3) δ 7.37-7.21
(m, 10H), 4.16 (s, 2H); 13C NMR (75 MHz, CDCl3) δ 137.6,
136.5, 129.9, 129.0, 128.6, 127.3, 126.5, 39.1. 1-Gram scale:
(629 mg, 71% yield).
ACKNOWLEDGMENT
The University of Texas at Arlington and the Research Enhance-
ment Program supported this work. The authors also recognize Dr.
Xiaojun Hung and Jonathan Lefton (UTA) for their assistance in
the synthesis of some azides and NMR analysis. Also, the Shimad-
zu Center for MS data collection and the NSF grants (CHE-
0234811 and CHE-0840509) for additional instrumentation.
General Procedure for the Synthesis of 4-Bromothiophenol
Derivatives. The respective triazene (0.3 mmol) and 4-
bromothiophenol (0.6 mmol) were dissolved in THF (0.5 mL)
and the mixture was stirred at room temperature for 1 h. The
volatiles were then removed under reduced pressure and ethyl
acetate (15 mL) was added. The solution was washed with 10%
NaOH solution (3 x 10 mL). The organic layer was dried over
Na2SO4 and the volatiles were removed under reduced pres-
sure. The crude mixture was then purified using column chro-
matography with silica gel and Hexanes/Dichloromethane (1:1)
as mobile phase to afford products 15g-i.
REFERENCES
(1) For select examples see: (a) Swain, S. P. Synlett 2014, 25, 2085-
2086; (b) Felzmann, W.; Castagnolo, D.; Rosenbeiger, D.; Mulzer, J.
J. Org. Chem. 2007, 72, 2182.
(2) Cowper, P.; Jin, Y.; Turton, M. D.; Kociok-Köhn, G.; Lewis, S.
E. Angew. Chem. Int. Ed. 2016, 55, 2564-2568 and references therein.
(3) For select examples see: (a) Storr, T. E.; Greaney, M. F. Org.
Lett. 2013, 15, 1410-1413; (b) Charpentier, J.; Früh, N.; Togni, A.
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M.; Pleixats, R.; Álvarez-Larena, Á.; Martin, E.; Vallribera, A.; Shafir,
A. Angew. Chem. Int. Ed. 2014, 53, 11298-11301.
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I. J. Org. Chem. 2015, 80, 6400-6410; (b) Chen, J.-Y.; Chen, X.-L.;
Li, X.; Qu, L.-B.; Zhang, Q.; Duan, L.-K.; Xia, Y.-Y.; Chen, X.; Sun,
K.; Liu, Z.-D.; Zhao, Y.-F. Eur. J. Org. Chem. 2015, 2015, 314-319;
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Benzhydryl(4-bromophenyl)sulfane (15g). White solid. (31 mg,
29% yield). mp: 98-100 °C; IR (neat) ν 3076, 1561, 1489, 694
1
cm-1; H NMR (300 MHz, CDCl3) δ 7.45-7.40 (m, 4H), 7.34-
7.21 (m, 8H), 7.11-7.07 (m, 2H), 5.52 (s, 1H); 13C NMR (75
MHz, CDCl3) δ 140.6, 135.3, 132.1, 131.9, 128.8, 128.5,
127.6, 120.8, 57.6; HRMS (ESI) m/z 355.0151, calcd for
C19H16BrS [M+H]+ 355.0156.
(4-bromophenyl)(1-phenylethyl)sulfane (15h). Colorless oil.
(29 mg, 33% yield). IR (neat) ν, 3085, 1570, 1470, 697 cm-1;
1H NMR (300 MHz, CDCl3) δ 7.52 (d, J = 2.1 Hz, 4H), 7.43-
7.31 (m, 5H), 5.09 (q, J = 6.9 Hz, 1H), 1.85 (d, J = 6.5 Hz,
3H); 13C NMR (75 MHz, CDCl3) δ 142.9, 134.3, 134.1, 131.9,
128.6, 127.4, 127.3, 121.4, 48.2, 22.3; HRMS (ESI) m/z
290.9838, calcd for C14H12BrS [M-H]+ 290.9840.
Benzyl(4-bromophenyl)sulfane (15i). Known compound.43
1
White solid. (44 mg, 53% yield). H NMR (300 MHz, CDCl3)
δ 7.37 (d, J = 8.6 Hz, 2H), 7.30-7.26 (m, 5H), 7.15 (d, J = 8.6
7
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