Synthetic and mechanistic aspects of cross-coupling of nitroxyl radicals of 3-imidazoline series with terminal alkynes

Article abstract of DOI:10.1016/j.tet.2008.06.088

Practical synthetic approaches to the new class of acetylenic derivatives of 3-imidazolyl-3-oxide-1-oxyls, including biradicals, were developed through cross-coupling reactions of 3-imidazolyl halides with either terminal alkynes or their copper salts. The presence of nitroxyl functional group as an internal oxidant leads to a competition between the formation of cross-coupling products and the products of oxidative homocoupling. The balance in this competition can be shifted toward the cross-coupling products through the combination of factors that includes nature of the catalyst, reactivity of the halides, and reaction conditions.

Full text of DOI:10.1016/j.tet.2008.06.088

Tetrahedron 64 (2008) 8807–8814
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthetic and mechanistic aspects of cross-coupling of nitroxyl radicals
of 3-imidazoline series with terminal alkynes
,
a
b
c,
*
Sergei F. Vasilevsky a , Olga L. Krivenko , Vitalii R. Gorelik , Igor V. Alabugin
*
a Institute of Chemical Kinetics and Combustion, Siberian Branch of the Russian Academy of Science, 630090 Novosibirsk, Russian Federation
b International Tomography Center, Novosibirsk, Siberian Branch of the Russian Academy of Science, 630090 Novosibirsk, Russian Federation
c Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Practical synthetic approaches to the new class of acetylenic derivatives of 3-imidazolyl-3-oxide-1-oxyls,
including biradicals, were developed through cross-coupling reactions of 3-imidazolyl halides with
either terminal alkynes or their copper salts. The presence of nitroxyl functional group as an internal
oxidant leads to a competition between the formation of cross-coupling products and the products of
oxidative homocoupling. The balance in this competition can be shifted toward the cross-coupling
products through the combination of factors that includes nature of the catalyst, reactivity of the halides,
and reaction conditions.
Received 29 January 2008
Received in revised form 20 June 2008
Accepted 24 June 2008
Available online 27 June 2008
Keywords:
Nitronylnitroxyl radicals (NNR)
Terminal alkynes
Ó 2008 Elsevier Ltd. All rights reserved.
Copper salts of alkynes
Cross-coupling
Homocoupling
3-Imidazolyl-3-oxide-1-oxyls
Transition metal catalysis
1. Introduction
can participate in electron delocalization. Both of these factors are
often important for studies of magnetic and optical properties. If
Stable nitroxyl radicals continue to draw significant attention of
researchers working at the interface between chemistry, physics,
and biology. Traditionally, radicals of this family have been widely
used as spin probes in biochemistry1 and in the design of para-
magnetic complexes in coordination chemistry.2 New areas of
application for these molecules continue to emerge, most recently
in studies of intricate details of intramolecular interactions and spin
catalysis.3,4
Stringent requirements to structural, electronic, and steric pa-
rameters often complicate development of new materials with
designed magnetic and optical properties. In this context, radicals
with ethynyl moieties are promising because the HChC-group is
a rigid, convenient scaffold for construction of spin-labeled mole-
cules with programmable electronic, geometric, and magnetic
parameters. On one hand, increased acidity of the methine protons
allows facile functionalization of such molecules through the cre-
ation of new C–C bonds. On the other hand, the –ChC-linkage
ensures the rigid spatial arrangement of functional moieties and
needed, partial hydrogenation of the ChC-bond allows one to
prepare the respective cis- and trans-alkene derivatives in trans-
formations, which change molecular geometry but preserve con-
jugation. Another valuable property of alkyne functionality is its
ability to undergo facile cycloaddition reactions5–7 useful for the
attachment of spin labels to biomolecules. Finally, full hydrogena-
tion of the triple bond can be used to drastically decrease the ex-
change interaction. For example, this problem had to be addressed
in the studies of the fundamental aspects of spin catalysis in re-
combination of spin-correlated ion-radical pairs. In these studies,
hydrogenation of acetylenic derivatives of nitroxyl radicals of
2-imidazolyl family permitted for the first time detection of the
magnetic effect (15%) in recombination of ion-radical pairs.3
However, more detailed quantitative studies required the further
decrease in the exchange interaction between the spin center and
the ion-radical pair. Such decrease could be achieved in nitroxyls of
3-imidazolyl family where the paramagnetic center is separated
from the aromatic molecule with two single bonds.
It is important to emphasize that although chemistry of 3-imi-
dazolylnitroxyls is well-developed, information regarding synthe-
sis of acetylenic derivatives with this core has not been available
before the initiation of our research program in this field. From our
point of view, this situation is not due to the lack of interest to
* Corresponding authors. Fax: þ1 7 383 3307350 (S.F.V.).
E-mail addresses: vasilev@kinetics.nsc.ru (S.F. Vasilevsky), alabugin@chem.fsu.
edu (I.V. Alabugin).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.06.088

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S.F. Vasilevsky et al. / Tetrahedron 64 (2008) 8807–8814
acetylenyl-3-imidazolinyl nitroxyls but rather a result of synthetic
difficulties illustrated in this paper.
of ca. 90% of the dehydrodimer (homocouple) of phenylacetylene
along with the hydroxylamine derived from the starting
4
From this perspective, the development of synthetic approaches
to acetylenic derivatives of 3-imidazolyl is necessary for the general
progress of chemistry of nitroxyl radicals because the reactivity of
the triple bond opens access to numerous transformations of the
paramagnetic molecules. The presence of two highly reactive
functional groups establishes the significance of acetylenyl-
3-imidazoline-3-oxide-1-oxyls as promising building blocks of
multipurpose utility.
Recently, we published two short communications describing
the first representatives of this class of compounds.8,9 In the pres-
ent paper, we provide full experimental details and spectral prop-
erties of these molecules and expand the list of prepared nitroxyls
through the introduction of a more diverse set of substituents of
different chemical nature. In addition, we will compare three
alternative cross-coupling techniques, and analyze their scope,
limitations, and mechanistic features.
p-bromoimidazoline 3.
Earlier,11 we observed for the first time the anomalous forma-
tion of such oxidative coupling products from terminal alkynes in
the absence of an external oxidant in the reaction of 3-acylamino-
1-methyl-4-iodopyrazole with phenylacetylene or hexyne-1.
However, in the earlier report, dehydrodimers were formed
through a sequence, which included oxidative addition/reductive
elimination of the alkyne derivatives and exchange of hydride to
iodide anion. At the end, the iodine atom of aryl halide played the
role of the oxidant. In the present case, the mechanism may be
different due to the possible involvement of either the nitrone or
the nitroxyl groups as the oxidant (Scheme 2).
In order to test this hypothesis and get further insight into the
mechanism, we carried out the model experiments, which utilized
nitroxyls 5 and 7 lacking halogen atoms in the aromatic ring
(Scheme 2). The TLC analysis confirmed that neither the hydrox-
ylamines 6 and 8 nor the dehydrodimer 4 are formed when radicals
5 and 7 are stirred with triethylamine and phenylacetylene in
benzene at 80 ꢀC for 5 h in the atmosphere of argon. However, once
Pd(PPh3)2Cl2 catalyst (20 mol %) was added, nitroxyl radicals 5 and
7 were reduced in the respective hydroxylamines 6 (66%) and 8
(91%) with the concomitant formation of dehydrodimer 4 (66–74%).
In the presence of PdCl2 and a stronger base (AcONa$3H2O), for-
mation of dehydrodimer 4 (66–90%) and hydroxylamines 6 or 8
was observed even at the room temperature in the course of 8 h.
The yields of diamagnetic products 6 and 8 were 28% and 94%,
respectively.
2. Results and discussion
Our initial attempts of using the classic approach to the prepa-
ration of alkynes through dehydrohalogenation of the respective
vic-dihalides with such strong bases as KOH in DMSO or refluxing
ethanol, or with KOH in the presence of tetrabutylammonium
bromide (TBAB) turned out to be unsuccessful and only led to
considerable decomposition.8 This result prompted us to consider
the most widely applied alternative modern method for the prep-
aration of aryl(hetaryl)alkynesdthe Sonogashira cross-coupling of
terminal alkynes with aryl(hetaryl)halides.10 However, interaction
of paramagnetic bromide 1 with phenylacetylene under the
Sonogashira conditions [Pd(PPh3)2Cl2, CuI, PPh3, Et3N, 80 ꢀC] in
benzene was unsuccessful as well (Scheme 1).
These observations illustrate that the nitroxyl group needs the
assistance of the Pd salts to serve as an oxidant. Although the exact
mechanism of this assistance is unknown, it is possible that the role
of Pd catalyst is in the formation of p-complex possessing a weak-
ened C–H bond, which increases the reductive properties of the
terminal alkyne. On the other hand, direct homolytic cleavage of
In the course of this reaction, we observed only trace amounts of
the desired product 2. The main reaction path included formation
O-
N+
N
2 (trace)
HO
O-
N+
O-
N+
Pd(PPh3)2Cl2,
PPh3, CuI,
Et3N. 80 °C
N
N
Br
Br
O
HO
3
1
44%
4
90%
Scheme 1.
X
X
-
O
+
-
O
+
+
N
N
i or ii
N
OH
N
O
4
5: X=H
7: X=NO2
.
6: X=H
8: X=NO2
6 (66%), 4 (66%);
8 (91%), 4 (74%)
i: Pd(PPh3)2Cl2, CuI, Et3N, C6H6, Ar, 80 °C
6 (28%), 4 (90%);
8 (94%), 4 (66%)
.
ii: PdCl2, AcONa 3H2O, CuI, CH3CN, Ar,80 °C
Scheme 2.

S.F. Vasilevsky et al. / Tetrahedron 64 (2008) 8807–8814
8809
the very strong sp-hybridized C–H bond is thermodynamically
unfavorable. It is worth noting that this is the first example of ox-
idative coupling of a terminal alkyne under the cross-coupling
conditions in the absence of an external oxidant.
Considering the formation of the side products in the reactions
of nitroxyls catalyzed by Pd-complexes, we applied the acetylide
method12 for the synthesis of spin-labeled acetylenic compounds
using both the paramagnetic and the diamagnetic p-iodoimidazo-
lines (9 and 10) and m-iodoimidazoline 11 as the substrates
(Scheme 3).
such simple acetylenic alcohols and amines as 3-methylbut-1-yn-
3-ol, N-morpholinoprop-1-yne, etc., cannot form the copper salts.
Considering all of the above, we decided to utilize a different
modification of cross-coupling, which used Cu catalysis in the ab-
sence of Pd in the [K2CO3, CuI, Et3N, PPh3, DMF, 110 ꢀC] system14
(Scheme 4). Under these conditions (110 ꢀC, DMF, 13 h), we were
able to isolate the diamagnetic target cross-coupling product 2.
However, the yield was low (27%) and, again, the reaction was
accompanied by the formation of hydroxylamine 3 (44%) and
dehydrodimer 4 (71%).
We supposed that the copper salt plays the same role here as in
the Pd-catalyzed processes described above. In order to test this
hypothesis, we carried out a model experiment described in
Scheme 5.
Neither hydroxylamine 8 nor dehydrodimer 4 was formed when
a mixture of radical 7, phenylacetylene, and potassium carbonate
was refluxed in DMF for 4 h under the atmosphere of argon. On the
other hand, addition of a catalytic amount of CuI to the reaction
mixture led to the reduction of the nitroxyl radical 7 to the re-
spective hydroxylamine 8 (68%) and to the formation of the dehy-
drodimer 4 (71%) in 2 h. These results show that the nitroxyl moiety
can behave as an oxidant not only in the presence of Pd catalyst but
also in the presence of the Cu(I) salts as well.
O-
N+
O-
N+
Cu
R
.
N
Py, 80 - 85 °C
N
.
O
I
(OH) O
R
p: 9 (10)
m: 11
p: 12, 14 -17
m: 13
33 - 91%
12
13
14
15
16
17
R =
N
O
NO2
O
N
O
N
O
O
O
Br
Although examples of oxidative coupling of terminal alkynes in
the presence of Pd catalysts can be found in the literature, only
external oxidants (such as iodine,15 triethylamine oxide,16 chloro-
acetone,17 etc.) were used. Thus, we were the first to describe the
cases when the substrate itself serves as an oxidant in such catalytic
processes.
Nevertheless, formation of the target products even in the low
yields suggested that use of more reactive iodides instead of bro-
mides may increase the relative importance of cross-coupling. In-
deed, when the iodohydroxylamine 10 or 18 was used, the reaction
promoted by the [K2CO3, CuI, Et3N, PPh3, DMF] system at 110 ꢀC led
to the formation of the target acetylenyl derivatives 19–24 (53–83%,
Scheme 6). This method was also successfully applied for the
synthesis of the biradical product 25 (45%, Scheme 7).
Scheme 3.
Interaction of iodoimidazolines 9–11 with copper acetylides in
refluxing pyridine under the argon atmosphere13 led to the for-
mation of the spin-labeled acetylenes 12–17 in 33–91%. Either the
paramagnetic iodide 9 or its diamagnetic precursor 10 can be used
in the reaction without the need to oxidize the hydroxylamine 10.
The yields and selected properties of the spin-labeled alkynes
12–17 are summarized in Section 4.
However, despite the overall attractiveness of acetylide method
for the modification of 3-imidazolinenitroxyles, this approach has
an important shortcoming since it requires an additional step for
the preparation of copper acetylides. Not only some compounds of
this class are explosive but also many terminal alkynes, in particular
-
O
+
N
N
2
HO
-
27%
-
O
+
N
O
N+
.
N
Br
O
K2CO3
CuI, PPh3
DMF, 110 °C
N
Br
1
HO
3
44%
4
71%
Scheme 4.
NO2
NO2
O-
N
O-
N+
+
K2CO3
+
+
CuI, PPh3, DMF
80 °C
N
OH
N
O
4
8
.
7
71%
68%
Scheme 5.

8810
S.F. Vasilevsky et al. / Tetrahedron 64 (2008) 8807–8814
O-
N+
O-
N+
H
R
.
K2CO3
CuI, PPh3
DMF, 110 °C
N
N
O
HO
I
R
p: 10
p: 20 - 24
m: 19
m: 18
53 - 83%
H3C
CH3
R =
19
20
21
22
23
24
NH2
O
N
N
N
O
O
H3C
Scheme 6.
O-
cross- and homocoupling are competing processes, one can expect
that the competition between them may be perturbed by a change
in temperature. Indeed, such approach allowed us to carry out
successful synthesis of the spin-labeled alkynes. For example, in the
reaction of p- and m-iodides 9 and 11 with trimethylsilyl acetylene
under the standard Sonogashira conditions ([Pd(PPh3)2]Cl2–CuI,
Et3N) at 40 ꢀC in benzene, the yields of TMS-alkynes 26 and 27
reached 91% and 77%, respectively (Scheme 8).
N+
I
N
HO
10
K2CO3
CuI, DMF, 110 °C
O-
N+
O-
N+
N
O.
N
.
25
45%
O
O-
N+
O-
N+
Si
Scheme 7.
Pd(PPh3)2Cl2
CuI, Et3N
40 °C
N
.
I
N
.
O
p-: 26 (91%)
m-: 27 (77%)
O
Section 4 summarizes the reaction yields and times as well as
p-: 9
m-: 11
Si
the selected physical and spectral properties for compounds
obtained via this method. The formation of dehydrodimers from
the aryl bromides and successful cross-coupling of their iodo ana-
logues suggests that homocoupling and cross-coupling compete
with each other and that the latter process dominates when the
more reactive iodides are used.
Although this method seems the most general, it also has
a shortcoming because the high reaction temperature (110 ꢀC) is
necessary. This requirement does not allow one to carry out the
reactions with low-boiling reagents such as trimethylsilyl acetylene
(bp 53 ꢀC), which is the key reagent for the preparation of terminal
alkynes.
Scheme 8.
Under the same conditions, the paramagnetic p-iodoimidazo-
line 9 interacts with phenylacetylene to yield a mixture of dia- and
paramagnetic products 2 and 12 (31% and 54%, respectively,
Scheme 9). As expected from the formation of product 2, the
homocoupling product 4 was also observed (25% isolated yield).
This observation suggests that the balance between cross- and
homocoupling in Pd-catalyzed reactions of nitroxyl radicals re-
mains rather subtle and can be potentially controlled by a number
of experimental variables.
The successful results obtained for the iodo derivatives
prompted us to reinvestigate the efficiency of Pd-catalyzed cross-
coupling processes at the lower temperatures. Considering that the
Under these conditions, the diamagnetic iodide 28 reacts with
4,40-diethynylbiphehyl with the formation of biradical 29 in 62%
yield (Scheme 10).
O-
N+
N
2
O-
N+
HO
31%
H
Pd(PPh3)2Cl2, CuI
Et3N, 40 °C
I
+
O-
N+
N
.
O
9
N
.
12
O
54%
Scheme 9.
O-
N+
O-
N
O-
N+
I
N
N
N
Pd(PPh3)2Cl2, CuI, Et3N
.
HO
.
O
O
29
28
62%
Scheme 10.

S.F. Vasilevsky et al. / Tetrahedron 64 (2008) 8807–8814
8811
The paramagnetic TMS-substituted nitronylnitroxides 26 and 27
4.2. Method A. General procedure of acetylides cross-
coupling reaction
can be converted into terminal acetylenylimidazolines 30 (79%) and
31 (48%) via removal of the silyl protecting group under mild
conditions (MeOH, K2CO3, 40 ꢀC, Scheme 11).
A mixture of copper(I) salt of acetylene (0.36 mmol) and para-
magnetic iodides 9 or 11 or diamagnetic iodide 10 (130 mg,
0.33 mmol) in 10 mL of pyridine was stirred at 80–85 ꢀC in argon
atmosphere till absence of iodide (TLC-control). Then CHCl3 (30 ml)
and water (40 mL) were added. The organic layer was separated,
the water layer was extracted with CHCl3 (2ꢃ25 mL), and the
combined organic layers were washed with 25% NH3aq (2ꢃ15 mL),
dried over Na2SO4, filtered off through Al2O3, and evaporated to
dryness under reduced pressure. The crude product was purified
by column chromatography on Al2O3 (elution with chloroform).
Subsequent recrystallization gave pure compounds 12–17.
O-
N+
O-
N+
K2CO3
CH3OH
N
O• N
O•
p: 26
p: 30 (79%)
m: 31 (48%)
H
Si
m: 27
Scheme 11.
3. Conclusions
4.2.1. 2,2,5,5-Tetramethyl-4-{2-[p-(phenyl)ethynylphenyl]vinyl}-
3-imidazoline-3-oxide-1-oxyl (12)
In summary, we investigated three modifications of the cross-
coupling of halogen-substituted nitroxyles of 3-imidazolyl family
with terminal alkynes and their copper salts. We found that only
iodides are suitable substrates for cross-coupling of halo-3-imi-
dazolylnitroxyls with terminal alkynes. The Castro method is ap-
plicable to copper salts of a variety of alkynes with the exception
of several simplest amines and alcohols. The catalytic version of
cross-coupling with the [K2CO3, CuI, Et3N, PPh3, DMF] system is
general for all terminal alkynes with sufficiently high boiling
points but requires a high temperature (110 ꢀC). On the other
hand, the catalytic Sonogashira [Pd(PPh3)2Cl2, CuI, Et3N] system
has the advantage of allowing cross-coupling under the lower
temperatures but, sometimes, at the expense of partial conversion
of the alkyne to the respective oxidative homocoupling product.
Under the Sonogashira conditions, the bromo-3-imidazoline
nitroxyls act mainly as oxidants and transform terminal acetylenes
into their dehydrodimers.
The time of reaction is 6 h,ꢂth1 e yield of 12 is 83.3%, mp 197.5–
(ChC). HRMS, m/z (%): 359.1 [Mþ] (15.40), 344.2 (31.44), 329.2
(37.78), 314.2 (44.47), 312.2 (70.76), 271.2 (38.51), 257.1 (64.78),
242.1 (56.20), 215.1 (52.66). Found: m/z 359.17540 [Mþ]. C23H23N2O2
198.5 ꢀC (from benzene). IR, cm
, n: 1253 (N/O),1364 (N–O), 2216
calcd: M¼359.17594. UV (EtOH), lmax/nm (lg
3): 201 (2.15), 235
(0.87), 273 (0.54), 283 (0.61), 360 (2.18). ESR: giso¼2.0058
(D
HDPPH¼3.79 G), AN¼14.05 G, AH(CH3)(12H)¼0.23 G, A(13C)¼5.66 G.
Solvent: toluene.
4.2.2. 2,2,5,5-Tetramethyl-4-{2-[p-(2,3,5,6,8,9,11,12-octahydro-
1,4,7,10,13-pentaoxabenzocyclopentadecen-15-yl-ethynyl)-
phenyl]vinyl}-3-imidazoline-3-oxide-1-oxyl (15)
The time of reaction is 2 h, the yield of 15 isꢂ517.0%, mp 178.5–
180.0 ꢀC (from mixture benzene–hexane). IR, cm
, n: 2205 (ChC),
2868, 2934, 2930, 2983 (CH3). HRMS, m/z (%): 549.2 [Mþ] (15.31),
534.1 (31.71), 504.1 (24.31), 502.2 (45.38), 448.3 (12.07), 447.3
(35.54), 343.1 (11.61), 295.2 (18.03),189.2 (6.38),180.1 (23.58),163.1
(33.76), 98.2 (28.67). Found: m/z 549.25942 [Mþ]. C31H37N2O7
Overall, this work developed convenient practical approaches to
acetylenic 3-imidazolyl nitroxyles, compounds, which can serve as
the multipurpose building blocks for the preparation of spin probes
of a new generation.
calcd: M¼549.26006. UV (EtOH), lmax/nm (lg
3): 205 (1.43), 245
(0.63), 271 (0.52), 326 (0.73), 349 (1.11), 3.72 (1.21). ESR:
giso¼2.0059 ( HDPPH¼4.10 G), AN¼13.74 G, AH(CH3)(12H)¼0.22 G, A
D
4. Experimental
4.1. General
(
13C)¼5.57 G. Solvent: toluene.
4.2.3. 2,2,5,5-Tetramethyl-4-{2-[p-(bromophenyl)ethynyl-
phenyl]vinyl}-3-imidazoline-3-oxide-1-oxyl (16)
Melting points were determined with a hot-stage microscope.
Column chromatography was performed on silica gel (Merck 60,
70–230 mesh). The Rf values were measured on aluminum backed
TLC plates (silica gel 60 F254, Merck, 0.2 mm) with the indicated
eluent. Mass spectra (HRMS) were measured on a Finnigan
SSQd710 at 70 eV using electron impact modes. Combustion ele-
mental analysis was performed for the non-volatile compounds 25
and 29 instead of high-resolution mass spectrometry. The IR-
spectra were recorded on a Bruker IFS 66 spectrometer (potassium
bromide). ESR spectra were taken in degassed solutions on a Bruker
EMX CW ESR spectrometer, all hyperfine coupling constants and
field offsets from standard DPPH line are given in Gauss with ac-
curacy ꢁ0.02 G, except for the couplings with methyl carbon-13 for
which the accuracy is ꢁ0.1 G, concentration of radicals 10ꢂ5 to
10ꢂ4 M in the indicated solvent. 1H NMR spectra were recorded on
a Bruker DRX 400 (9.4 Tesla, 400.13 MHz) spectrometer. Chemical
The time of reaction is 5 h, tꢂh1e yield of 16 is 91.0%, mp 192.4–
193.6 ꢀC (from benzene). IR, cm
, n: 2212 (ChC). HRMS, m/z (%):
437.0 [Mþ] (6.34), 410.1 (7.24), 407.0 (35.07), 394.0 (39.32), 391.9
(100.00), 350.9 (37.18), 349.9 (45.67), 294.9 (37.56), 257.1 (9.18),
239.1 (50.58),176.0 (23.43),150.0 (11.40),135.1 (30.55), 98.1 (24.57).
Found: m/z 437.08795 [Mþ]. C23H22N2O2Br calcd: M¼437.08651. UV
(EtOH), lmax/nm (lg
ESR: giso¼2.0057
3): 200 (1.56), 236 (0.65), 288 (0.48), 364 (1.61).
(DHDPPH¼3.6 G), AN¼14.09 G, AH(CH3)(12H)¼
0.23 G, A (13C)¼5.72 G. Solvent: toluene.
4.2.4. 2,2,5,5-Tetramethyl-4-{2-[m-(N-ethoxyethyl-1H-pyrazol-4-
ylethynyl)phenyl]vinyl}-3-imidazoline-3-oxide-1-oxyl (13)
The time of reaction is 4.5 h, the yield of 13 is 76.5%, mp 141.0–
142.0 ꢀC (from mixture benzene–hexane). IR, cmꢂ1
, n: 2224
(ChC). HRMS, m/z (%): 421.2 [Mþ] (3.90), 391.1 (63.55), 374.1
(43.14), 261.1 (38.46), 260.1 (22.86), 247.2 (22.34), 205.1 (34.52),
73.1 (43.57), 45.1 (100.00). Found: m/z 421.22844 [Mþ].
shifts (d, ppm) are given from internal CHCl3 (7.24). Coupling con-
stants (J, Hz) were accurate to ꢁ0.2 Hz for 1H. Compound 1 was
prepared by previously reported methods.10 Copper(I) acetylides
were prepared according to the published procedure11 from the
corresponding acetylenes.18–20 Commercial phenylacetylene, (tri-
methylsilyl)acetylene, and PdCl2(PPh3)2 (‘Aldrich’) were used
without additional purification.
C
24H29N4O3 calcd: M¼421.22395. UV (EtOH), lmax/nm (lg
3): 202
(1.22), 237 (1.11), 282 (1.44), 294 (1.56), 335 (1.23). ESR:
giso¼2.0059 ( HDPPH¼3.85 G), AN¼14.06 G, AH(CH3)(12H)¼0.23 G, A
D
(
13C)¼5.73 G. Solvent: toluene.

8812
S.F. Vasilevsky et al. / Tetrahedron 64 (2008) 8807–8814
4.2.5. 2,2,5,5-Tetramethyl-4-{2-[p-(2-pyridinylethynyl)-
phenyl]vinyl}-3-imidazoline-3-oxide-1-oxyl (14)
4.3.3. 2,2,5,5-Tetramethyl-4-{2-[p-(acetylphenyl)ethynyl-
phenyl]vinyl}-3-imidazoline-3-oxide-1-oxyl (21)
The time of reaction is 2.5 h, the yield of 14 isꢂ313.0%, mp 179.9–
The time of reaction is 4.5 h, the yield of 21 is (53.3%), mp 179.0–
180.0 ꢀC (from mixture benzene–hexane). IR, cm
,
n
: 2221 (ChC),
180.5 ꢀC (from mixture benzene–hexane). IR, cmꢂ1
, n: 1264 (N/O),
2862, 2936, 2981 (CH3). HRMS, m/z (%): 363.0 [Mþ] (11.73), 361.9
(44.62), 359.9 (19.52), 330.0 (61.01), 314.9 (73.31), 312.9 (100.00),
271.8 (54.00), 257.9 (88.27), 241.9 (37.30), 231.8 (30.33), 215.9
(51.74). Found: m/z 360.17256 [Mþ]. C22H22N3O2 calcd:
1361 (N–O), 1674 (C]O), 2212 (ChC). HRMS, m/z (%): 401.2 [Mþ]
(5.31), 386.2 (14.34), 371.1 (21.04), 356.1 (32.30), 354.1 (44.52), 312.9
(20.09), 299.0 (32.62). Found: m/z 401.18722 [Mþ]. C25H25N2O3
calcd: M¼401.18650. UV (EtOH), lmax/nm (lg
3
): 324 (4.39). ESR
M¼360.17119. UV (EtOH), lmax/nm (lg
3
): 200 (1.57), 228 (0.76), 270
giso¼2.0062 (
D
HDPPH¼4.29 G), AN¼14.04 G, AH(CH3)(12H)¼0.23 G.
(0.48), 359 (2.18). ESR: giso¼2.0059 (
DHDPPH¼4.05 G), AN¼13.81 G,
Solvent: toluene.
AH(CH3)(12H)¼0.23 G, A (13C)¼5.60 G. Solvent: toluene.
4.3.4. 2,2,5,5-Tetramethyl-4-{2-[p-(2-carbomethoxyphenyl)-
ethynylphenyl]vinyl}-3-imidazoline-3-oxide-1-oxyl (22)
The time of reaction is 2.5 h, the yield of 22 is 56.2%, mp 239.0–
4.2.6. 2,2,5,5-Tetramethyl-4-{2-[p-(o-nitrophenyl)ethynyl-
phenyl]vinyl}-3-imidazoline-3-oxide-1-oxyl (17)
The time of reaction is 2 h, ꢂth1 e yield of 16 is 53.0%, mp 179.0–
239.5 ꢀC (from benzene). IR, cmꢂ1
, n: 1254 (N/O),1367 (N–O),1739
180.0 ꢀC (from benzene). IR, cm
,
n
: 1252 (N/O),1341 (N–O), 2216
(C]O), 2214 (ChC). HRMS, m/z (%): 417.2 [Mþ] (17.48), 387.2
(38.26), 372.1 (56.79), 370.1 (100.00), 329.1 (29.87), 314.1 (40.57),
283.1 (51.02). Found: m/z 417.17921 [Mþ]. C25H25N2O4 calcd:
(ChC). HRMS, m/z (%): 404.2 [Mþ] (12.86), 374.2 (61.66), 359.1
(62.03), 358.1 (25.08), 357.1 (100.00), 299.1 (25.59), 258.1 (19.88),
239.0 (15.16), 183.1 (43.56). Found: m/z 404.16220 [Mþ].
M¼417.18142. UV (EtOH), lmax/nm (lg
3): 238 (4.28), 285(3.95), 365
(4.61). ESR giso¼2.0061 ( HDPPH¼4.5 G), AN¼14.06 G, AH(CH3)(12H)¼
C
23H22N3O4 calcd: M¼404.16102. UV (EtOH), lmax/nm (lg
3
): 203
D
(1.81), 228 (1.21), 264 (0.85), 373 (2.78), 382 (2.27). ESR:
0.23 G, A (13C)¼5.575 G. Solvent: toluene.
giso¼2.0059 ( HDPPH¼3.85 G), AN¼14.06 G, AH(CH3)(12H)¼0.23 G, A
D
(
13C)¼5.736 G. Solvent: toluene.
4.3.5. 2,2,5,5-Tetramethyl-4-{2-[p-(2-amino-4-methylpyridinyl-5)-
ethynylphenyl]vinyl}-3-imidazoline-3-oxide-1-oxyl (23)
4.3. Method B. General procedure of Pd-free cross-coupling
reaction
The time of reaction is 3.5 hꢂ, t1he yield of 23 is 75.0%, mp 202.5–
(ChC). HRMS, m/z (%): 389.0 [Mþ] (7.90), 359.1(5.30), 344.1 (11.32),
203.0 ꢀC (from benzene). IR, cm
, n: 1253 (N/O),1364 (N–O), 2206
A mixture of iodide 10 or 18 (150 mg, 0.39 mmol), PPh3
(0.04 mmol), CuI (0.02 mmol), potassium carbonate (0.6 mmol),
and alkyne (0.4 mmol) in 10 mL of DMF was stirred under stream
of argon at 90–100 ꢀC until the full consumption of iodide (TLC-
control, ‘Silufol’). Then CHCl3 (30 ml) and water (40 mL) were
added, organic layer was separated and the aqueous layer was
extracted with CHCl3 (2ꢃ25 mL). The combined organic layers
were washed with 25% aqueous NH3 (2ꢃ15 mL), dried over K2CO3,
filtered through Al2O3, and evaporated to dryness under reduced
pressure. The crude product was purified by column chromatog-
raphy on Al2O3 (elution with chloroform). Subsequent re-
crystallization gave pure compounds 19–25. Physical and spectral
data for the products are given in following sections. Note for
compound 25: a mixture of iodide 10 (130 mg, 0.33 mmol), PPh3
(0.04 mmol), CuI (0.02 mmol), potassium carbonate (0.6 mmol),
and 4,40-diethynylbiphehyl (33 mg, 0.16 mmol) in 10 mL of DMF
was used.
342.1 (22.28), 286.9 (9.81), 244.9 (10.78). Found: m/z 389.19693
[Mþ]. C23H25N4O2 calcd: M¼389.19774. UV (EtOH), lmax/nm (lg
3):
255 (4.18), 277 (4.21), 377 (4.59). ESR: giso¼2.0060 ( HDPPH¼4.05 G),
D
AN¼14.05 G, AH(CH3)(12H)¼0.23 G, A (13C)¼5.72 G. Solvent: toluene.
4.3.6. 2,2,5,5-Tetramethyl-4-{2-[p-(pyrimidinyl-5)ethynylphenyl]-
vinyl}-3-imidazoline-3-oxide-1-oxyl (24)
The time of reaction is 7 h, thꢂe1yield of 24 is 53.0%, mp 147.0–
148.0 ꢀC (from benzene). IR, cm
, n: 1255 (N/O), 1366 (N–O),
2216 (ChC). HRMS, m/z (%): 361.2 [Mþ] (11.17), 346.2 (32.86), 331.2
(64.91), 314.2 (95.94), 273.1 (64.75), 272.1 (66.67), 244.0 (78.94),
217.2 (82.34), 177.1 (40.24), 78.0 (60.81). Found: m/z 361.16545
[Mþ]. C21H21N4O2 calcd: M¼361.16644. UV (EtOH), lmax/nm (lg
3):
226 (4.16), 357 (4.49). ESR giso¼2.0061
(D
HDPPH¼4.39 G),
AN¼14.05 G, AH(CH3)(12H)¼0.23 G, A (13C)¼5.88 G. Solvent: toluene.
4.3.7. Bis-4,40-{2,2,5,5-tetramethyl-4-[2-(p-ethynylphenyl)vinyl]-
3-imidazoline-3-oxide-1-oxyl}-biphenyl (25)
4.3.1. 2,2,5,5-Tetramethyl-4-{2-[m-(phenyl)ethynylphenyl]vinyl}-3-
imidazoline-3-oxide-1-oxyl (19)
The time of reaction is 3 h, the yield of 25 is 45.5%, mp 254.0–
255.5 ꢀC (from benzene). IR, cmꢂ1
, n: 1255 (N/O), 1364 (N–O),
The time of reaction is 5 h, ꢂth1e yield of 19 is 83.3%, mp 156.5–
2211 (ChC). Anal. Calcd for C46H44N4O4: C, 77.07; H, 6.19; N, 7.82.
Found: C, 76.95; H, 6.42; N, 7.80. UV spectra were not taken due to
158.0 ꢀC (from benzene). IR, cm
,
n
: 1255 (N/O),1364 (N–O), 2116
(ChC). HRMS, m/z (%): 359.1 [Mþ] (6.62), 354.9 (83.62), 329.1
(96.31), 312.0 (60.45), 270.0 (39.74), 214.9 (71.07), 170.0 (52.00).
Found: m/z 359.17647 [Mþ]. C23H23N2O2 calcd: M¼359.17594. UV
low solubility in ethanol. ESR giso¼2.0060
(
D
HDPPH¼4.22 G),
AN¼14.13 G, AH(CH3)(12H)¼0.23 G, A (13C)¼5.83 G. Solvent: toluene.
(EtOH), lmax/nm (lg
ESR: giso¼2.0061
3
): 217 (0.71), 284 (098), 300 (0.98), 335 (0.67).
HDPPH¼4.42 G), AN¼14.07 G, AH(CH3)(12H)¼
4.4. Method C. General procedure of Pd catalyst cross-
coupling reaction
(D
0.23 G, A (13C)¼5.90 G. Solvent: toluene.
A mixture of iodide 9 or 11 (150 mg, 0.39 mmol), [Pd(PPh3)2]Cl2
(20 mg), PPh3 (40 mg), CuI (20 mg), Et3N (5 mL), and alkyne
(0.4 mmol) in 20 mL of benzene was stirred under stream of argon
at 80 ꢀC until the full consumption of iodide (TLC-control, ‘Silufol’).
Then the mixture filtered through Al2O3 and evaporated to dryness
under reduced pressure. The crude product was purified by column
chromatography on Al2O3 (elution with benzene). Subsequent re-
crystallization gave pure compounds 2, 12, 26, 27, and 29. Physical
and spectral data for the products are given in the following sec-
tions. Note for biradical 25: a mixture of iodide 28 (150 mg,
0.40 mmol), [Pd(PPh3)2]Cl2 (20 mg), PPh3 (40 mg), CuI (20 mg),
4.3.2. 2,2,5,5-Tetramethyl-4-{2-[p-(diphenyl)ethynylphenyl]vinyl}-
3-imidazoline-3-oxide-1-oxyl (20)
The time of reaction is 4 h, thꢂe1yield of 20 is 71.4%, mp 147.0–
148.0 ꢀC (from benzene). IR, cm
, n: 1255 (N/O), 1368 (N–O),
2213 (ChC). HRMS, m/z (%): 435.2 [Mþ] (13.79), 405.2 (29.00),
390.2 (56.62), 388.2 (100.00), 347.2 (62.17), 318.3 (34.32), 291.2
(54.24), 252.2 (19.13). Found: m/z 435.20869 [Mþ]. C29H27N2O2
calcd: M¼435.20724. UV (EtOH), lmax/nm (lg
3): 203 (1.56), 240
(0.96), 257 (1.04), 342 (1.97). ESR: giso¼2.0060 ( HDPPH¼4.05 G),
D
AN¼14.05 G, AH(CH3)(12H)¼0.23 G, A (13C)¼5.72 G. Solvent: toluene.

S.F. Vasilevsky et al. / Tetrahedron 64 (2008) 8807–8814
8813
Et3N (5 mL), and 4,40-diethynylbiphehyl (42 mg, 0.20 mmol) in
20 mL of benzene was used.
evaporated to dryness under reduced pressure. The crude product
was purified by column chromatography on Al2O3 (elution with
benzene). Subsequent recrystallization gave pure products.
4.4.1. 1-Hydroxy-2,2,5,5-tetramethyl-4-{2-[p-(phenyl)ethynyl-
phenyl]vinyl}-3-imidazoline-3-oxide (2)
For radical 5 the yield of 1-hydroxy-2,2,5,5-tetramethyl-
4-phenyl-3-imidazoline-3-oxide 6 is 66%, mp 188.5–189.5 ꢀC (from
mixture of benzene–hexane), mp(lit.) 193.0–194.0 ꢀC.22 The yield of
1,4-diphenylbuta-1,3-diyne 4 is 66.5%, mp 83.0–85.0 ꢀC (from
hexane), mp(lit.) 86.0–87.0 ꢀC.
The time of reaction is 4.5 h, the yield of 2 is 31%, mp 218–
219.5 ꢀC (from benzene). IR, cmꢂ1
, n: 1257 (N/O), 2217 (ChC),
3230 (OH). 1H NMR: 1.52 (s, 6H, CH3), 1.62 (s, 6H, CH3), 4.85 (br s,
1H, OH), 6.86 (d, 1H, ]CH–Im, J¼16.2), 7.26–7.57 (m, 9H, Ar), 8.42
(d, 1H, ]CH–Ar, J¼16.2). HRMS, m/z (%): 360.0 [Mþ] (25.11), 312.0
(20.85), 286.9 (21.52), 257.9 (42.73), 256.9 (100.00), 241.8 (79.39),
240.9 (34.38), 218.8 (19.20), 214.8 (24.10). Found: m/z 360.18393
For radical
7 the yield of 1-hydroxy-2,2,5,5-tetramethyl-
4-(p-nitrophenyl)-3-imidazoline-3-oxide 8 is 91%, mp 83.4–84.5 ꢀC
(from mixture of benzene–hexane), mp(lit.) 85.0–87.0 ꢀC.24 The
yield of 1,4-diphenylbuta-1,3-diyne 4 is 74%, mp 85.5–86.5 ꢀC (from
hexane), mp(lit.) 86.0–87.0 ꢀC.23
[Mþ]. C23H24N2O2. calcd: M¼360.18377. UV (EtOH), lmax/nm (lg
3):
227 (0.12), 284 (0.10), 359 (0.24). 1,4-Diphenylbuta-1,3-diyne 4
Method ii: a solution of radical 5 or 7 (2.0 mmol), AcONa$3H2O
(0.08 g, 0.58 mmol) and phenylacetylene (2.4 mmol, 240 mg,
0.3 mL), PdCl2 (5 mg) in 8 mL of CH3CN was stirred under stream of
argon at 20 ꢀC for 8 h. Then the mixture was evaporated to dryness
under reduced pressure and filtered through Al2O3 (elution with
ethyl acetate). Subsequent recrystallization gave pure compounds 6
or 8 and 4.
[10 mg (25%)] was isolated as well.
4.4.2. 2,2,5,5-Tetramethyl-4-{2-[p-(phenyl)ethynylphenyl]vinyl}-3-
imidazoline-3-oxide-1-oxyl (12)
The time of reaction is 4.5 h, the yield of 12 is 54.0%, mp 197.5–
198.5 ꢀC (from benzene). Spectral and analytical data see above
(in Section 4.2).
For radical
5 the yield of 1-hydroxy-2,2,5,5-tetramethyl-
4-phenyl-3-imidazoline-3-oxide 6 is 28%, mp 188.5–189.5 ꢀC (from
mixture of benzene–hexane), mp(lit.) 193.0–194.0 ꢀC.22 The yield of
1,4-diphenylbuta-1,3-diyne 4 is 90%, mp 85.5–86.5 ꢀC (from hex-
ane), mp(lit.) 86.0–87.0 ꢀC.23
4.4.3. 2,2,5,5-Tetramethyl-4-{2-[p-(trimethylsilyl)-
ethynylphenyl]vinyl}-3-imidazoline-3-oxide-1-oxyl] (26)
The time of reaction is 3 h, the yield of 26 is 91.0%, mp 184.0–
185.0 ꢀC (from mixture benzene–hexane), mp(lit.) 184.0–185.0 ꢀC.21
For radical
7 the yield of 1-hydroxy-2,2,5,5-tetramethyl-
IR, cmꢂ1
,
n
: 1252 (N/O), 1362 (N–O), 2157 (ChC), HRMS, m/z (%):
4-(p-nitrophenyl)-3-imidazoline-3-oxide 8 is 94%, mp 84.0–85.0 ꢀC
(from mixture of benzene–hexane), mp(lit.) 85.0–87.0 ꢀC.24 The
yield of 1,4-diphenylbuta-1,3-diyne 4 is 66%, mp 83.5–85.0 ꢀC (from
hexane), mp(lit.) 86.0–87.0 ꢀC.23
355.1 [Mþ] (22.84), 325.1 (43.98), 310.1 (56.54), 309.1 (22.75), 308.1
(73.41), 267.1 (38.07), 266.1 (33.91), 252.1 (24.26), 211.0 (16.03).
Found: m/z 355.18055 [Mþ]. C20H27N2O2Si calcd: M¼355.18417. UV
(EtOH), lmax/nm (lg 3): 243 (4.08), 251 (4.08), 352 (4.52). ESR
giso¼2.0060 (
D
HDPPH¼4.184 G), AN¼14.29 G, AH(CH3)(12H)¼0.24 G, A
4.6. General procedure of desilylation of 26 and 27
(
13C)¼5.82 G. Solvent: toluene.
A mixture of radical 26 or 27 (0.33 g, 0.9 mmol) and K2CO3
(0.12 g, 0.9 mmol) in 15 mL of methanol was stirred under of argon
at room temperature until TLC-control (‘Silufol’) indicates absence
of the starting materials (4 h). At this point, CHCl3 (20 ml) and
water (40 mL) were added, organic layer was separated and the
aqueous layer was extracted with CHCl3 (2ꢃ25 mL). The organic
layers were combined, dried over K2CO3, filtered through Al2O3,
and evaporated to dryness under reduced pressure. The crude
product was purified by column chromatography on Al2O3 (elution
with chloroform). Subsequent recrystallization gave pure com-
pounds 30 and 31.
4.4.4. 2,2,5,5-Tetramethyl-4-{2-[m-(trimethylsilyl)-
ethynylphenyl]vinyl}-3-imidazoline-3-oxide-
1-oxyl (27)
The time of reaction is 7 h, the yield of 27 is 77.0%, mp 144.0–
144.5 ꢀC (from mixture benzene–hexane), mp(lit.) 144.0–144.5 ꢀC.21
IR, cmꢂ1
, n: 1258 (N/O), 1368 (N–O), 2156 (ChC). HRMS, m/z (%):
360.0 [Mþ] (25.11), 312.0 (20.85), 286.9 (21.52), 257.9 (42.73), 256.9
(100.00), 241.8 (79.39), 240.9 (34.38), 218.8 (19.20), 214.8 (24.10).
Found: m/z 355.18373 [M]þ. C20H27N2O2Si calcd: M¼355.18417. UV
(EtOH), lmax/nm (lg 3): 202 (4.21), 231 (4.34), 247 (4.35), 263 (4.01),
272 (4.27), 336 (4.32). ESR giso¼2.0061
(
D
HDPPH¼4.262 G),
AN¼14.09 G, AH(CH3)(12H)¼0.23 G,
A
(
13C)¼5.913 G. Solvent:
4.6.1. 2,2,5,5-Tetramethyl-4-{2-[p-(ethynyl)phenyl]vinyl}-3-
imidazoline-3-oxide-1-oxyl (30)
toluene.
Yield is 78.9%, mp 176.0–176.6 ꢀC (from mixture benzene–hex-
4.4.5. Bis-4,40-[4-(p-ethynylphenyl)-2,2,5,5-tetramethyl-3-
imidazoline-3-oxide-1-oxyl]-biphenyl (29)
ane), mp(lit.) 176.0–176.6 ꢀC.21 IR, cmꢂ1
, n: 1254 (N/O), 1361 (N–O),
2110 (ChC). HRMS, m/z (%): 283.1 [Mþ] 33.31, 253.0 (100.00), 238.0
(72.42), 236.1 (84.63), 194.9 (47.73), 193.9 (75.10), 179.9 (48.82),
165.9 (54.81), 164.9 (70.52), 152.9 (40.80), 138.9 (97.80). Found: m/z
The time of reaction is 5 h, the yield of 29 isꢂ611.5%, mp 242.0–
242.5 ꢀC (from mixture benzene–hexane). IR, cm
, n: 1256 (N/O),
1360 (N–O), 2213 (ChC). Anal. Calcd for C42H40N4O4: C, 75.88; H,
6.06; N, 8.43. Found: C, 76.60; H, 6.07; N, 8.54. UV spectra were not
taken due to low solubility of compounds 25 and 29 in ethanol. ESR
283.14430 [Mþ]. C17H19N2O2 calcd: M¼283.14463. UV (EtOH), lmax
/
nm (lg
3
): 242 (0.83), 249 (0.82), 346 (1.89). ESR giso¼2.00587
(D
HDPPH¼3.9 G), AN¼14.01 G, AH(CH3)(12H)¼0.23 G, A (13C)¼5.97 G.
giso¼2.0059 (
D
HDPPH¼3.95 G), AN¼14.16 G, AH(CH3)(12H)¼0.23 G, A
Solvent: toluene.
(
13C)¼6.3 G. Solvent: toluene.
4.6.2. 2,2,5,5-Tetramethyl-4-{2-[m-(ethynyl)phenyl]vinyl}-3-
imidazoline-3-oxide-1-oxyl (31)
4.5. General procedure of Pd catalyst cross-coupling reaction
for model compounds 5 and 7
Yield is 48.0%, mp 141.5–142.0 ꢀC (from mixture benzene–hex-
ane), mp(lit.) 141.5–142.0 ꢀC.21 IR, cmꢂ1
, n: 1254 (N/O), 1361 (N–O),
Method i: a solution of radical 5 or 7 (2.0 mmol), Et3N (5 mL) and
phenylacetylene (240 mg, 2.4 mmol, 0.30 mL) in 20 mL of benzene
was stirred under stream of argon at 80 ꢀC for 5 h. Then
[Pd(PPh3)2]Cl2 (20 mg) was added and the mixture was stirred at
80 ꢀC for another 5 h. The mixture was filtered through Al2O3, and
2110 (ChC). HRMS, m/z (%): 2853.1 [Mþ] (11.92), 253.2 (100.00),
238.2 (42.99), 236.2 (44.49), 194.1 (54.97), 165.1 (64.51), 149.0
(37.29), 139.1 (71.73). Found: m/z 283.14521 [M]þ. C17H19N2O2
calcd: M¼283.14464. UV (EtOH), lmax/nm (lg
3): 201 (1.04),
224 (1.81), 256 (1.13), 265 (0.92), 333 (1.62). ESR giso¼2.0060

8814
S.F. Vasilevsky et al. / Tetrahedron 64 (2008) 8807–8814
13C)¼
6. Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed. 2001, 40, 2004–
2021.
7. Photochemical version: Zeidan, T.; Kovalenko, S. V.; Manoharan, M.; Clark, R. J.;
Ghiviriga, I.; Alabugin, I. V. J. Am. Chem. Soc. 2005, 127, 4270–4285; Zeidan, T.;
Clark, R. J.; Kovalenko, S. V.; Ghiviriga, I.; Alabugin, I. V. Chem.dEur. J. 2005, 11,
4953–4962.
8. Vasilevsky, S. F.; Klyatskay, S. V.; Korovnikova, O. L.; Amitina, S. A.; Stass, D. V.;
Grigor’ev, I. A.; Elguero, J. Tetrahedron Lett. 2004, 45, 7741–7743.
9. Vasilevsky, S. F.; Krivenko, O. L.; Alabugin, I. V. Tetrahedron Lett. 2007, 48, 8246–
8249.
10. Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975, 50, 4467–4470.
11. Tretyakov, E.; Knight, D.; Vasilevsky, S. J. Chem. Soc., Perkin Trans. 1 1999, 3713–
3720.
(
D
HDPPH¼4.22 G), AN¼14.13 G, AH(CH3)(12H)¼0.23 G,
A
(
5.83 G. Solvent: toluene.
Acknowledgements
The authors are grateful to Dr. D. V. Stass for measuring of ESR
spectra, Dr. S. A. Amitina for a sample of compounds 6, 8, 10, and 18,
Dr. S. V. Klyatskaya for 25.
This work was supported by grant of RFBR 07-03-00048-a, grant
‘Integration’ of SB of Russian Academy of Sciences No. 54 (2006–
2008) and No. 32 (2006–2008) and grant CRDF RUXO 008-NO-06.
12. Stephens, R. D.; Castro, C. E. J. Org. Chem. 1963, 28, 3313–3315.
13. Vasilevsky, S.; Klyatskaya, S.; Korovnikova, O.; Amitina, S.; Stass, D.; Grigor’ev, I.;
Elguero, J. Tetrahedron 2006, 62, 4597–4602.
14. Okuro, K.; Furuune, M.; Enna, M.; Miura, M.; Nomura, M. J. Org. Chem. 1993, 58,
4716–4721.
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