Cross-coupling of aryl iodides with paramagnetic terminal acetylenes derived from 4,4,5,5-tetramethyl-2-imidazoline-2-oxyl 3-oxide

Article abstract of DOI:10.1023/A:1015026200647

2-(Arylylethynylphenyl)-4,4,5,5-tetramethyl-2-imidazoline-1-oxyl 3-oxides 12 and 13 were synthesized by cross-coupling of aryl iodides with 1-alkynes containing the 4,4,5,5-tetramethyl-2-imidazoline-1-oxyl 3-oxide fragment. A procedure was developed for the preparation of 3-and 4-ethynyibenzaldehydes with the use of 2-methylbut-3-yn-2-ol.

Full text of DOI:10.1023/A:1015026200647

128
Russian Chemical Bulletin, International Edition, Vol. 51, No. 1, pp. 128—134, January, 2002
Crossꢀcoupling of aryl iodides with paramagnetic
terminal acetylenes derived from
4,4,5,5ꢀtetramethylꢀ2ꢀimidazolineꢀ1ꢀoxyl 3ꢀoxide
S. V. Klyatskaya,a E. V. Tretyakov,a and S. F. Vasilevskyb
aInstitute of Chemical Kinetics and Combustion, Siberian Branch of the Russian Academy of Sciences,
3 ul. Institutskaya, 630090 Novosibirsk, Russian Federation.
Fax: +7 (383 2) 39 7101. Eꢀmail: vasilev@ns.kinetics.nsc.ru
bNovosibirsk State University,
2 ul. Pirogova, 630090 Novosibirsk, Russian Federation
2ꢀ(Arylylethynylphenyl)ꢀ4,4,5,5ꢀtetramethylꢀ2ꢀimidazolineꢀ1ꢀoxyl 3ꢀoxides 12 and 13 were
synthesized by crossꢀcoupling of aryl iodides with 1ꢀalkynes containing the 4,4,5,5ꢀtetramethylꢀ
2ꢀimidazolineꢀ1ꢀoxyl 3ꢀoxide fragment. A procedure was developed for the preparation of 3ꢀ
and 4ꢀethynylbenzaldehydes with the use of 2ꢀmethylbutꢀ3ꢀynꢀ2ꢀol.
Key words: alkynes, crossꢀcoupling, nitroxyl radicals, aryl iodide, imidazoline oxide.
Previously,1 we have demonstrated that compounds
tion of iodoterphenyl with 4,4,5,5ꢀtetramethylꢀ2ꢀ(4ꢀ
ethynylphenyl)ꢀ2ꢀimidazolineꢀ1ꢀoxyl 3ꢀoxide.
with the structure A—Sp—R•, where A is the aromatic
group, R• is the stable radical center, and Sp is the bridgꢀ
ing fragment (spacer), are convenient models for studying
spin catalysis. It was found that the presence of the radical
In the present study, the reactions of (arylꢀ
ethynyl)benzaldehydes with BHA and crossꢀcoupling of
aryl iodides with paramagnetic terminal acetylenes, viz.,
derivatives of 4,4,5,5ꢀtetramethylꢀ2ꢀimidazolineꢀ1ꢀoxyl
3ꢀoxide, were examined in detail with the aim of preparꢀ
ing new 2ꢀ(arylethynylphenyl)imidazoline nitroxyls.
center R• in the ionꢀradical pair (alkane)•+ –•A—Sp—R•
/
leads to the disappearance or rapid (nanoseconds) atꢀ
tenuation of the magnetic effect in luminescence arising
from recombination of these pairs. This effect was obꢀ
served for pꢀterphenyl derivatives. To answer the question
about the influence of the nature of the luminophore A on
the magnetic effect, it is necessary to study substrates
of the A—Sp—R• type in which the luminophore is
varied, while the Sp and R• fragments remain unꢀ
changed. In this connection, we undertook the present
investigation in order to synthesize paramagnetic linear
aromatic compounds in which the aromatic group A
is regularly changed (phenyl, biphenylyl, and pꢀterꢀ
phenylyl).
Generally, derivatives of 2ꢀimidazoline nitroxyls are
synthesized by condensation of aldehydes or their synꢀ
thetic equivalents with 2,3ꢀbis(hydroxyamino)ꢀ2,3ꢀdiꢀ
methylbutane (BHA) or its monosulfate followed by oxiꢀ
dation of cyclic adducts with sodium periodate or lead
dioxide.2 This procedure was used for the preparaꢀ
tion of derivatives of 2ꢀ(ethynylphenyl)ꢀ2ꢀimidazoline
nitroxyls.3—8 Previously,1 we have failed to apply this
procedure to the synthesis of 2ꢀ(terphenylylethynylꢀ
phenyl)ꢀ2ꢀimidazoline nitroxyl from pꢀ(terphenylylꢀ
ethynyl)benzaldehyde. The target paramagnetic arylꢀ
acetylene has been synthesized in low yield by the reacꢀ
Results and Discussion
As mentioned above, the key stage of the synthesis of
2ꢀ(arylethynylphenyl)ꢀ2ꢀimidazolineꢀ1ꢀoxyl 3ꢀoxides acꢀ
cording to Ullman's procedure2 involves the reactions of
aldehydes with BHA. With this in mind, we prepared a
series of arylethynylbenzaldehydes 3a—c by crossꢀcouꢀ
pling of aryl iodides 1a—c with pꢀethynylbenzaldehyde
(2a) and then treated them with BHA. However, the reꢀ
actions of 4ꢀ(phenylethynyl)benzaldehyde (3a) or 4ꢀ(biꢀ
phenylylꢀ4ꢀethynyl)benzaldehyde (3b) with BHA in the
presence of atmospheric oxygen led to oxidation of aldeꢀ
hydes (instead of condensation) to form the correspondꢀ
ing carboxylic acids 4a,b in 55—65% yields irrespective of
whether the reactions were carried out in ethanol, benꢀ
zene, or tetrahydrofuran and regardless of the temperaꢀ
ture (ambient or higher). The reaction of BHA with 4ꢀ
([1,1´;4´,1″]terphenylꢀ4″ꢀylethynyl)benzaldehyde (3c) in
tetrahydrofuran afforded a poorly soluble compound
whose structure was not unambiguously established
(Scheme 1).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 122—127, January, 2002.
1066ꢀ5285/02/5101ꢀ128 $27.00 © 2002 Plenum Publishing Corporation

2ꢀArylꢀ2ꢀimidazolineꢀ1ꢀoxyl 3ꢀoxide
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 1, January, 2002
129
Scheme 1
calcined KOH powder or in an apparatus for sublimation
in the presence of KOH and vacuum oil.13 Under these
reaction conditions, compounds 6a,b underwent
resinification. Because of this, the aldehyde group in comꢀ
pounds 6a,b was reduced with NaBH4, the resulting
alcohols 7a,b were decomposed with KOH, and then comꢀ
pounds 8a,b were oxidized with PCC to obtain the target
ethynylbenzaldehydes 2a,b. We failed to apply this proceꢀ
dure to the synthesis of the оrthoꢀisomer. оꢀEthynylꢀ
benzaldehyde was prepared from 2ꢀiodobenzaldehyde acꢀ
cording to a procedure described previously.11
Condensation of aldehydes 2a,b with BHA monoꢀ
sulfate 9 gave rise to adducts 10a,b in 85% yields. Adducts
10a,b were oxidized with NaIO4 to obtain nitroxyls 11a,b.
Sulfate 9 was preferred over the free base (the reaction
with the use of the latter was described in the literature3)
because it is, first, more readily accessible and, second,
allowed us to obtain adducts 10a,b in higher yields. The
reaction of оꢀethynylbenzaldehyde with BHA or its
monosulfate 9 afforded a complex mixture of products,
which we failed to separate.
The reaction of spinꢀlabeled acetylene 11a with
pꢀiodotoluene (1d) in benzene in the presence of
PdCl2(PPh3)2, CuI, and Et3N at 55—80 °C gave rise to
2ꢀ(4ꢀethynylphenyl)ꢀ4,4,5,5ꢀtetramethylꢀ2ꢀimidazolineꢀ
1ꢀoxyl (19) (the yield was 12%) and compounds 16—18
(the yield was ∼65%). The structure of 16 was established
by comparing with the authentic sample.3 The structure
of compound 18 was proved by its independent synthesis
1: Ar = Ph (a),
(b),
(c)
Apparently, these results are associated with low reacꢀ
tivities of tolanꢀlike aldehydes 3a,b, which reacted not
with BHA but with hydrogen peroxide generated due to
oxidation of BHA with atmospheric oxygen.9 Actually,
aldehydes 3a—c were not oxidized under an inert atmoꢀ
sphere to yield carboxylic acids; however, their reactions
with BHA did not proceed as well. Under the reaction
conditions in the absence of BHA, aldehydes were not
transformed into acids 4.
Since attempts to prepare nitroxylꢀcontaining tolans
according to Ullman's procedure failed, we examined an
alternative approach to the synthesis in more detail. The
latter approach is based on crossꢀcoupling of the correꢀ
sponding iodoarenes with paramagnetic arylacetylenes
synthesized beforehand. This procedure for the preparaꢀ
tion of 2ꢀ(arylethynylphenyl)ꢀ2ꢀimidazoline nitroxyls has
been described in the literature.1,10 For example, crossꢀ
coupling of mꢀdiiodobenzene with 2ꢀ(3,5ꢀdiethynylꢀ
phenyl)ꢀ2ꢀimidazoline nitroxyl10 was applied in the synꢀ
thesis of nitroxyl polyradicals; the reaction was carried
out in pyridine in the presence of triethylamine using
PdCl2(PPh3)2 and CuI as the catalysts.
Scheme 2
The starting paramagnetic alkynes 11a,b were preꢀ
pared according to Scheme 2.
A procedure has been proposed11 for the preparation
of isomeric ethynylbenzaldehydes 2a,b based on the reacꢀ
tions of bromobenzaldehydes with trimethylsilylacetylene
followed by the removal of the trimethylsilyl group. We
synthesized aldehydes 2a,b based on the alkaline cleavage
of tertiary arylacetylenic alcohols (the retroꢀFavorskii reꢀ
action12), which were prepared by crossꢀcoupling of aryl
halides with 2ꢀmethylbutꢀ3ꢀynꢀ2ꢀol. The reactions of
halobenzaldehydes 5a,b with 2ꢀmethylbutꢀ3ꢀynꢀ2ꢀol in
the presence of Pd(OAc)2, PPh3, CuI, and Et3N afforded
acetylenic alcohols 6a,b in 90% yields. Tertiary acetylenic
alcohols are generally decomposed in anhydrous benzene
at 75—80 °C in the presence of catalytic amounts of a
a is paraꢀisomer, b is metaꢀisomer, X = 4ꢀBr (5a), 3ꢀI (5b)

130
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 1, January, 2002
Klyatskaya et al.
Scheme 3
involving reduction of biradical 16. The qualitative comꢀ
position of the reaction mixtures remained the same irreꢀ
spective of whether the reaction was carried out in Et3N
or in a mixture of Et3N and pyridine10 and regardless of
the reaction temperature (either ambient or higher). Conꢀ
ceivably, symmetrical biradicals 16 and 18 and unsymꢀ
metrical biradical 17 were formed due to successive or
competitive oxidation of the paramagnetic terminal alkyne
by another molecule of the starting nitronyl nitrоxide
giving rise to disubstituted butadiyne with the loss of the
nitroxide oxygen atom. To confirm this suggestion,
we carried out crossꢀcoupling of paramagnetic iodoꢀ
arene (2ꢀ(4ꢀiodophenyl)ꢀ4,4,5,5ꢀtetramethylꢀ2ꢀimidꢀ
azolineꢀ1ꢀoxyl 3ꢀoxide) with phenylacetylene in Et3N.
Actually, the latter reaction gave rise to diphenylbutaꢀ
1,3ꢀdiyne, 2ꢀ(4ꢀiodophenyl)ꢀ4,4,5,5ꢀtetramethylꢀ2ꢀimidꢀ
azolineꢀ1ꢀoxyl, and a small amount of the starting comꢀ
pound.
R1
=
, R2
=
,
R3
=
=
,
In continuation of the studies aimed at examining the
possibilities of the use of crossꢀcoupling for the preparaꢀ
tion of the target compounds, we attempted to perform
the reactions with adducts 10a,b and obtain copper
acetylides from compounds 10a,b and 11a,b in an effort
to employ the acetylide version of acetylenic condensaꢀ
tion. However, all our attempts failed.
R4
Ar =
(b);
(c);
It is known that crossꢀcoupling with the use of piperiꢀ
dine as a base proceeded much faster.14 Actually, crossꢀ
coupling of alkyne 11a with pꢀiodotoluene (1d) in piperiꢀ
dine in the presence of catalytic amounts of PdCl2(PPh3)2
and CuI afforded imidazolineꢀ1ꢀoxyl 3ꢀoxide (13d) in
58% yield. Simultaneously, we obtained 4,4,5,5ꢀtetraꢀ
methylꢀ2ꢀ[4ꢀ(4ꢀtolylethynyl)phenyl]ꢀ2ꢀimidazolineꢀ1ꢀ
oxyl (14d) (the yield was 16%) and biradicals 16, 17, and
18 (the total yield was ∼10%) (Scheme 3). The reactions
with iodides 1b,c,e,f gave rise to analogous series of the
products; the target nitronylnitroxyls 13b,c,e,f were obꢀ
tained in 20—60% yields. In addition, we isolated comꢀ
pound 15c from the products of the reaction of iodide 1c
with alkyne 11a. This fact indicates that the nitroxyl group
can be reduced to the amino group under the conditions
of crossꢀcoupling (Scheme 3).
In crossꢀcoupling, metaꢀisomer 11b behaved differꢀ
ently. In this case, the reaction take place not only in
piperidine but also in a pyridine—triethylamine mixture,10
the target nitronylnitroxyls 12b—d being obtained in higher
yields (65—85%) (see Scheme 3).
Hence, the course of crossꢀcoupling depends substanꢀ
tially on the reaction conditions and the structure of the
spinꢀlabeled alkyne.
pꢀTol (d),
n = 1 (e), 2 (f)
Reagents and conditions: i. Pd(PPh3)2Cl2, CuI, piperidine,
20—25 °C; ii. Pd(PPh3)2Cl2, CuI, Et3N (or Et3N—Py), 35—40 °C.
∼20 °C and the residue must be dissolved in benzene and
filtered through a layer of Al2O3. After this treatment, the
product was obtained in 65% yield and it was stable upon
storage.
To summarize, paramagnetic acetylenes of the aroꢀ
matic series were synthesized by crossꢀcoupling of aryl
iodides with 4,4,5,5ꢀtetramethylꢀ2ꢀphenylethynylꢀ2ꢀ
imidazolineꢀ1ꢀoxyl 3ꢀoxide.
Experimental
The 1H NMR spectra were recorded on a Bruker Avanceꢀ300
spectrometer. The IR spectra were measured on a Bruker IFSꢀ66
spectrometer in KBr pellets. The ESR spectra were recorded on
a Bruker EMX radiospectrometer at ∼20 °C; the concentrations
of the solutions were 5•10–5—5•10–4 mol L–1. The mass specꢀ
tra were obtained on a Finnigan SSQ−710 instrument using a
direct inlet system (EI, the ionizing voltage was 70 eV, the
It should be noted that compounds 13b—f are rather
labile under the conditions of crossꢀcoupling. Thus,
nitronylnitroxyl 13c, which was prepared by the reaction
of 1c with 11a, underwent complete deoxygenation to
compound 14c in ∼16 h. Hence, after completion of the
reaction, the solvents must be immediately removed at
o
temperature of the ionization chamber was 220—270 C). The
electronic absorption spectra were recorded on a Specord
UVꢀVIS spectrophotometer in MeOH at ∼20 °C. Column chroꢀ
matography was carried out on KSK silica gel (60/200 µm).

2ꢀArylꢀ2ꢀimidazolineꢀ1ꢀoxyl 3ꢀoxide
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 1, January, 2002
131
The course of the reactions and the purities of the comꢀ
pounds were monitored by TLC on Silufol UVꢀ254 plates.
3ꢀ(3ꢀHydroxyꢀ3ꢀmethylbutꢀ1ꢀynꢀ1ꢀyl)benzaldehyde (6b) was
prepared from 3ꢀiodobenzaldehyde (5b) analogously to 6a, the
yield was 94%, oil. 1H NMR (CD2Cl2), δ: 1.63 (s, 6 H, C(3)Me2);
2.08 (br.s, 1 H, OH); 7.54 (t, 1 H, H(5), J = 8.5 Hz); 7.71 (d,
1 H, H(4), J = 8.5 Hz); 7.86 (d, 1 H, H(6), J = 8.5 Hz); 7.97 (s,
1 H, H(2)); 9.97 (s, 1 H, CHO). IR, ν/cm–1: 1710 (C=O); 2220
(C≡C); 3560 (OH). Found (%): C, 76.82; H, 6.48. C12H12O2.
Calculated (%): C, 76.57; H, 6.43.
4″ꢀIodoꢀ[1,1´;4´,1″]terphenyl,1
4ꢀbromobenzaldehyde,15
3ꢀiodobenzaldehyde,16 4ꢀphenylethynylbenzaldehyde,17 2,3ꢀ
bis(hydroxyamino)ꢀ2,3ꢀdimethylbutane, and its monosulfate,18
2ꢀiodoꢀ6,7,9,10,12,13,15,16ꢀoctahydroꢀ5,8,11, 14,17ꢀpentaoxaꢀ
benzocyclopentadecene, 2ꢀiodoꢀ6,7,9,10,12,13,15,16,18,19ꢀ
decahydroꢀ5,8,11,14, 17,20ꢀhexaoxabenzocyclooctadecene,19
and PCC20 were prepared according to known procedures.
2ꢀIodobenzaldehyde21 was prepared from 2ꢀiodobenzyl alcoꢀ
hol22 according to a procedure described previously.20 2ꢀMethylꢀ
butꢀ3ꢀynꢀ2ꢀol (Aldrich), trimethylsilylacetylene (Fluka),
CuI, NaBH4, PPh3, Pd(OAc)2, and Pd[PPh3]2Cl2 (all from
Lancaster) were used without additional purification. Other reꢀ
agents and organic solvents were prepared according to standard
procedures.
4ꢀ[3ꢀ(Hydroxymethyl)phenyl]ꢀ2ꢀmethylbutꢀ3ꢀynꢀ2ꢀol (7b)
was prepared from acetylenic alcohol 6b analogously to 7a, the
1
yield was 91%, m.p. 63—64 °C. H NMR (CD2Cl2), δ: 1.51 (s,
6 H, C(2)Me2); 1.84 (t, 1 H, CH2OH, J = 5 Hz); 2.22 (s, 1 H,
OH); 4.67 (d, 2 H, CH2, J = 5 Hz); 7.28—7.37 (m, 3 H, H(4),
H(5), H(6)); 7.44 (s, 1 H, H(2)). IR, ν/cm–1: 2226 (C≡C);
3550 (OH). Found (%): C, 75.91; H, 7.51. C12H14O2. Calcuꢀ
lated (%): C, 75.76; H, 7.42.
4ꢀ(3ꢀHydroxyꢀ3ꢀmethylbutꢀ1ꢀynꢀ1ꢀyl)benzaldehyde (6a). A
mixture of 4ꢀbromobenzaldehyde (5a) (10.0 g, 54.1 mmol),
2ꢀmethylbutꢀ3ꢀynꢀ2ꢀol (7.9 mL, 81 mmol), Pd(OAc)2 (90 mg,
0.40 mmol), CuI (45 mg, 0.24 mmol), and PPh3 (180 mg,
0.69 mmol) in Et3N (11 mL) and benzene (20 mL) was stirred
under argon at 75—80 °C for 40 min. After completion of the
reaction, the cooled mixture was filtered through a layer of SiO2
(2.5×2 cm) and the solvent was removed in vacuo. The yield of
(3ꢀEthynylphenyl)methanol (8b) was prepared from tertiary
acetylenic alcohol 7b analogously to 8a, the yield was 62%, oil.
1H NMR (CDCl3), δ: 3.06 (s, 1 H, C≡CH); 4.79 (s, 2 H, CH2);
7.14—7.18 (m, 3 H, H(4), H(5), H(6)); 7.32 (s, 1 H, H(2)). IR,
ν/cm–1: 2260 (C≡C); 3260 (≡C—H); 3480 (OH). Found (%):
C, 81.81; H, 6.14. C9H8O. Calculated (%): C, 81.79; H, 6.10.
3ꢀEthynylbenzaldehyde (2b) was prepared from alcohol 8b
analogously to 2a, the yield was 74%, m.p. 76—76.5 °C.11
4ꢀ(Biphenylꢀ4ꢀylethynyl)benzaldehyde (3b). A mixture of
4ꢀiodobiphenyl 1b (1.57 g, 5.6 mmol), 4ꢀethynylbenzaldehyde
(2b) (0.78 g, 6.0 mmol), Pd(OAc)2 (60 mg, 0.27 mmol), CuI
(45 mg, 0.24 mmol), and PPh3 (180 mg, 0.69 mmol) in Et3N
(5 mL) and benzene (20 mL) was stirred under argon at 75—80 °C
for 6.5 h. After completion of the reaction, the cooled mixture
was filtered through a layer of SiO2 (2.5×2 cm), the solvent was
removed in vacuo, and the residue was crystallized from a benꢀ
zene—hexane mixture. The yield of 3b was 9.61 g (93%), m.p.
1
6a was 9.61 g (93%), oil. H NMR (CDCl3), δ: 1.68 (s, 6 H,
C(3)Me2); 1.85 (br.s, 1 H, OH); 7.56 (d, 2 H, H(3), H(5),
J = 7.5 Hz); 7.85 (d, 2 H, H(2), H(6), J = 7.5 Hz); 10.03 (s, 1 H,
CHO). IR, ν/cm–1: 1702 (C=O); 2226 (C≡C); 3404 (OH).
Found (%): C, 76.32; H, 6.52. C12H12O2. Calculated (%):
C, 76.57; H, 6.43.
4ꢀ[4ꢀ(Hydroxymethyl)phenyl]ꢀ2ꢀmethylbutꢀ3ꢀynꢀ2ꢀol (7a).
Solid NaBH4 (0.70 g, 19.0 mmol) was added to a stirred solution
of aldehyde 6a (9.60 g, 51.1 mmol) in MeOH (20 mL) at ∼20 °C.
After completion of the reaction, the reaction mixture was filꢀ
tered, the solvent was removed in vacuo, and the residue was
crystallized from trichloroethylene. The yield of 7a was 8.92 g
1
162—164 °C. H NMR (DMSOꢀd6), δ: 7.41 (t, 1 H, J = 8 Hz);
7.51 (t, 2 H, J = 8 Hz); 7.66—7.85 (m, 8 H); 7.97 (d, 2 H,
J = 9 Hz); 10.05 (s, 1 H, CHO). IR, ν/cm–1: 1697 (C=O); 2214
(C≡C). Found (%): C, 89.12; H, 5.08. C21H14O. Calculated (%):
C, 89.34; H, 5.00.
1
(92%), m.p. 83—84 °C. H NMR (DMSOꢀd6), δ: 1.48 (s, 6 H,
C(2)Me2); 4.51 (d, 2 H, CH2, J = 5 Hz); 5.22 (t, 1 H, CH2OH,
J = 5 Hz); 5.42 (s, 1 H, OH); 7.29—7.35 (m, 4 H, Ar).
IR, ν/cm–1: 2230 (C≡C); 3485 (OH). Found (%): C, 75.69;
H, 7.46. C12H14O2. Calculated (%): C, 75.76; H, 7.42.
4ꢀ([1,1´;4´,1″]Terphenylꢀ4″ꢀylethynyl)benzaldehyde (3c) was
prepared from 4ꢀphenylethynylbenzaldehyde and 2b analogously
to 3b, the yield was 64%, m.p. with decomp. 240—245 °C
1
(4ꢀEthynylphenyl)methanol (8a). A mixture of alcohol 7a
(6.80 g, 35.8 mmol) and calcined powdered KOH (2.10 g,
37.5 mmol) in benzene (30 mL) was refluxed for 2 h. After
cooling, the reaction mixture was filtered through a layer of
SiO2 (2.5×2 cm) and the solvent was removed in vacuo. The
product was extracted from the resulting oil with hot hexane
(5×40 mL) and the solvent was removed from the extract in
vacuo. The yield of 8a was 3.11 g (66%), m.p. 37—38.5 °C.
1H NMR (CDCl3), δ: 3.12 (s, 1 H, C≡CH); 4.74 (s, 2 H, CH2);
7.38 (d, 2 H, H(2), H(6), J = 7.5 Hz); 7.53 (d, 2 H, H(3), H(5),
J = 7.5 Hz). IR, ν/cm–1: 2260 (C≡C); 3260 (≡C—H); 3480
(OH). Found (%): C, 81.61; H, 6.15. C9H8O. Calculated (%):
C, 81.79; H, 6.10.
4ꢀEthynylbenzaldehyde (2a). A mixture of alcohol 8a (3.11 g,
23.5 mmol), PCC (5.65 g, 25.8 mmol), and CH2Cl2 (30 mL)
was stirred at ∼20 °C for 1 h. Then the reaction mixture was
filtered through a layer of silica gel, the solvent was distilled off
in vacuo, and the reaction product was sublimed at 100—110 °C
(15 Torr). The yield of 2a was 2.31 g (74%), m.p. 88—90 °C.11
(from Py). H NMR (DMSOꢀd6), δ: 7.41 (t, 1 H, J = 8 Hz);
7.51 (t, 2 H, J = 8 Hz); 7.66—7.85 (m, 8 H); 7.97 (d, 2 H,
J = 9 Hz); 10.05 (s, 1 H, CHO). IR, ν/cm–1: 1697 (C=O); 2214
(C≡C). Found (%): C, 90.21; H, 5.21. C27H18O. Calculated (%):
C, 90.47; H, 5.06.
4ꢀPhenylethynylbenzoic acid (4a). A mixture of 3a (0.1 g,
0.49 mmol), BHA (75 mg, 0.51 mmol), C6H6 (3 mL), and MeOH
(3 mL) was stirred at ∼20 °C for 5 days and the solvents were
distilled off. The residue was dissolved in THF, filtered through
a layer of SiO2, and crystallized from C6H6. The yield of 4a was
60 mg (55%). 1H NMR (Pyꢀd5), δ: 7.11—7.34 (m, 2 H);
7.45—7.68 (m, 5 H); 8.22 (d, 2 H, J = 9 Hz). IR, ν/cm–1: 2220
(C≡C); 3480 (OH). Highꢀresolution mass spectrum. Found:
m/z 222.06880 [M]+. C15H10O2. Calculated: M = 222.06807.
4ꢀ(Biphenylꢀ4ꢀylethynyl)benzoic acid (4b) was isolated in the
reaction of aldehyde 3b with BHA, the yield was 61%, m.p.
297—298 °C (from C6H6). 1H NMR (Pyꢀd5), δ: 7.11—7.34
(m, 3 H); 7.45—7.68 (m, 8 H); 8.19 (d, 2 H, J = 9 Hz). IR,
ν/cm–1: 2220 (C≡C); 3420 (OH). Highꢀresolution mass specꢀ

132
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 1, January, 2002
Klyatskaya et al.
trum. Found: m/z 298.10020 [M]+. C21H14O2. Calculated:
M = 298.09937.
C33H29N2O2. Calculated: M = 485.2189. ESR: aN (2 N) =
0.73 mT, aHꢀo (2 H) = 0.075 mT, aH(Me) (12 H) = 0.021 mT.
4,5ꢀDihydroꢀ1Hꢀimidazole (15c). Paleꢀyellow crystals, m.p.
249—251 °C (C6H6—hexane). IR, ν/cm–1: 825, 846, 880, 956,
1002, 1018, 1110, 1140, 1157, 1182, 1221, 1264, 1292, 1308,
1366, 1403, 1448, 1482, 1508, 1534, 1609, 2214, 2930, 2976
1,3ꢀDihydroxyꢀ2ꢀ(4ꢀethynylphenyl)ꢀ4,4,5,5ꢀtetramethylimidꢀ
azolidine (10a). A hot (50—56 °C) solution of 2,3ꢀbis(hydroxyꢀ
amino)ꢀ2,3ꢀdimethylbutane monosulfate monohydrate (9)
(3.55 g, 13 mmol) in H2O (20 mL) was added to a hot (50—55 °C)
solution of aldehyde 2a (1.71 g, 13 mmol) in MeOH (13 mL).
Then the reaction mixture was kept at ∼20 °C for one day and
neutralized with NaHCO3 (1.55 g). The residue was filtered off
and recrystallized from a benzene—CHCl3 mixture. The yield of
10a was 2.84 g (83%), m.p. 184—185 °C.3
2ꢀ(4ꢀEthynylphenyl)ꢀ4,4,5,5ꢀtetramethylꢀ2ꢀimidazolineꢀ1ꢀ
oxyl 3ꢀoxide (11a). Solid NaIO4 (4.11 g, 19.1 mmol) was
added portionwise to a stirred mixture of adduct 10a (3.32 g,
12.8 mmol), water (60 mL), and CH2Cl2 (60 mL) at 10—15 °C
for 1 h. The organic layer was separated and the aqueous layer
was extracted with CHCl3 (3×20 mL). The combined organic
extracts were filtered through a layer of Al2O3 (2×5 cm), the
solvent was distilled off, and the residue was crystallized from a
3 : 1 hexane—benzene mixture. The yield of 11a was 2.55 g
(78%), m.p. 131—132 °C.3
1,3ꢀDihydroxyꢀ2ꢀ(3ꢀethynylphenyl)ꢀ4,4,5,5ꢀtetramethylimidꢀ
azolidine (10b) was prepared from aldehyde 2b analogously to 10a,
the yield was 87%, m.p. 161—162 °C (from CHCl3—AcOEt, 1 : 1)
(cf. lit. data5: m.p. 151—153 °C). 1H NMR (DMSOꢀd6), δ: 0.99 (s,
6 H, C(4)Me, C(5)Me); 1.12 (s, 6 H, C(4)Me, C(5)Me); 4.13 (s,
1 H, C≡CH); 4.49 (s, 1 H, CH); 7.29—7.41 (m, 2 H, H(5), H(6));
7.48 (d, 1 H, H(4), J = 8.5 Hz); 7.59 (s, 1 H, H(2)); 7.83 (s,
2 H, NOH).
1
3034, 3441. H NMR (CD2Cl2), δ: 1.55 (s, 12 H, Me); 7.10
(br.s, 1 H, NH); 7.22 (t, 1 H, 4″ꢀH); 7.32 (t, 2 H, 3″, 5″ꢀH);
7.41—7.54 (m, 4 H, H arom.); 7.63—7.77 (m, 8 H, H arom.);
7.88 (d, 2 H, 2,6ꢀH). MS, m/z (Irel (%)): 454.2 [M]+ (2.76),
397.0 (14.27), 357.0 (6.69), 355.9 (33.34), 354.9 (86.68),
326.0 (1.78), 252.0 (3.63), 226.0 (0.74), 151.9 (1.0), 84.0
(100), 69.0 (46.45), 57.0 (1.49), 42.0 (7.64), 41.0 (22.19), 39.0
(1.02), 27.9 (53.33). Highꢀresolution mass spectrum. Found:
m/z 454.2388 [M]+. C33H30N2. Calculated: M = 454.2409.
2ꢀImidazolineꢀ1ꢀoxyl (14c). The yield was 15%, the IR specꢀ
trum and Rf are identical with those of authentic radical 14c (see
below).
2,2´ꢀ[(Butaꢀ1,3ꢀdiyneꢀ1,4ꢀdiyl)diꢀpꢀphenylene]ꢀbis(4,4,5,5ꢀ
tetramethylꢀ2ꢀimidazolineꢀ1ꢀoxyl 3ꢀoxide) (biradical 16): the
IR spectrum and Rf are identical with those of authentic
radical 16.3
1ꢀ[4ꢀ(4,4,5,5ꢀTetramethylꢀ2ꢀimidazolineꢀ1ꢀoxylꢀ2ꢀyl
3ꢀoxide)phenyl]ꢀ4ꢀ[4ꢀ(4,4,5,5ꢀtetramethylꢀ2ꢀimidazolineꢀ1ꢀ
oxylꢀ2ꢀyl)phenyl]butaꢀ1,3ꢀdiyne (biradical 17): Rf and the color
of the spot of biradical 17 are identical with those of an intermeꢀ
diate in the reaction of 16 with NaNO2.
Biradical 18: the IR spectrum and Rf are identical with those
of authentic radical 18 (see below).
2ꢀ(3ꢀEthynylphenyl)ꢀ4,4,5,5ꢀtetramethylꢀ2ꢀimidazolineꢀ1ꢀ
oxyl 3ꢀoxide (11b) was prepared from adduct 10b analogously to
11a, the yield was 89%, m.p. 138—139 °C (from a 2 : 1 hexꢀ
ane—benzene mixture).6
4,4,5,5ꢀTetramethylꢀ2ꢀ[4ꢀ(pꢀtolylethynyl)phenyl]ꢀ2ꢀimidꢀ
azolineꢀ1ꢀoxyl 3ꢀoxide (13d) was prepared analogously to 13c,
the yield was 58%, m.p. 148.5—150 °C (from a 3 : 1 hexꢀ
ane—benzene mixture). IR, ν/cm–1: 819, 841, 1127, 1166, 1216,
1300, 1362, 1388, 1421, 1449, 1478, 1509, 1599, 2213, 2979,
3030. ESR: aN (2 N) = 0.73 mT, aH(Me) (12 H) = 0.024 mT.
Found (%): C, 76.15; H, 6.53; N, 8.03. C22H23N2O2. Calcuꢀ
lated (%): C, 76.05; H, 6.67; N, 8.06. In addition, 4,4,5,5ꢀ
tetramethylꢀ2ꢀ[4ꢀ(pꢀtolylethynyl)phenyl]ꢀ2ꢀimidazolineꢀ1ꢀoxyl
(14d) was isolated from the reaction mixture. The yield was
16%, m.p. 126—127 °C (from a 3 : 1 hexane—benzene mixture).
ESR: aN1 (1 N) = 0.91 mT, aN3 (1 N) = 0.45 mT. Found (%):
C, 79.75; H, 6.91; N, 8.29. C22H23N2O. Calculated (%):
C, 79.73; H, 6.99; N, 8.45. In addition, biradicals 16—18 were
isolated (the total yield was 10%).
4,4,5,5ꢀTetramethylꢀ2ꢀ[4ꢀ([1,1´;4´,1″]terphenylꢀ4ꢀylꢀ
ethynyl)phenyl]ꢀ2ꢀimidazolineꢀ1ꢀoxyl 3ꢀoxide (13c). Alkyne 11a
(0.45 g, 1.8 mmol) was added portionwise to a mixture of
iodoterphenyl 1c (0.42 g, 1 mmol), Pd[PPh3]2Cl2 (40 mg,
0.057 mmol), CuI (20 mg, 0.11 mmol), and piperidine (10 mL)
under a stream of argon for 1 h. The solvent was removed in
vacuo with the use of an oil pump (∼0.1 Torr) at ∼20 °C,
the residue was dissolved in benzene, the solution was filꢀ
tered through a layer of Al2O3, and the solvent was distilled
off. The residue was dissolved in benzene and twice chroꢀ
matographed on silica gel. Elution with benzene afforded
0.1 g of 4,4,5,5ꢀtetramethylꢀ2ꢀ[4ꢀ([1,1´;4´,1″]terphenylꢀ4ꢀylꢀ
ethynyl)phenyl]ꢀ4,5ꢀdihydroꢀ1Hꢀimidazole (15c) (the yield was
19%), 60 mg of 4,4,5,5ꢀtetramethylꢀ2ꢀ[4ꢀ([1,1´;4´,1″]terphenylꢀ
4ꢀylethynyl)phenyl]imidazolineꢀ1ꢀoxyl (14c) (the yield was
10%), and 0.11 g of imidazolineꢀ1ꢀoxyl 3ꢀoxide (13c) (20%).
Elution with chloroform yielded a mixture (0.16 g) containing
dimer 16 and its iminonitroxyl analogs 17 and 18.
Imidazolineꢀ1ꢀoxyl 3ꢀoxide (13c). Blueꢀgreen crystals (from
benzene); at 238 °C, the compounds was transformed into orꢀ
ange imidazolineꢀ1ꢀoxyl 14c. IR, ν/cm–1: 2213 (C≡C); 2988
(Me); 3030 (C—H arom.). MS, m/z (Irel (%)): 485.0 [M]+
(14.39), 454.0 (9.04), 439.0 (3.74), 398.0 (17.40), 396.9 (52.65),
356.9 (15.70), 355.9 (44.46), 354.9 (100), 329.0 (2.12), 327.90
(3.38), 253.0 (1.25), 251.9 (3.99), 151.9 (1.43), 114.0 (28.70),
84.1 (88.31), 69.1 (27.46), 56.0 (11.29), 41.0 (14.64), 28.0 (4.78).
Highꢀresolution mass spectrum. Found: m/z 485.2166 [M]+.
Compounds 13b,e,f were prepared analogously to 13c
(byꢀproducts, which were identified by TLC and were not
isolated).
2ꢀ[4ꢀ(Biphenylꢀ4ꢀylethynyl)phenyl]ꢀ4,4,5,5ꢀtetramethylꢀ2ꢀ
imidazolineꢀ1ꢀoxyl 3ꢀoxide (13b). The yield was 29%, m.p.
188—190 °C (from a hexane—benzene mixture). IR, ν/cm–1
:
815, 837, 1000, 1019, 1065, 1103, 1129, 1166, 1214, 1302, 1363,
1388, 1423, 1449, 1485, 1526, 1600, 2213, 2928, 2987, 3032.
ESR: aN (2 N) = 0.73 mT, aH(Me) (12 H) = 0.024 mT.
Found (%): C, 79.31; H, 6.23; N, 6.63. C27H25N2O2. Calcuꢀ
lated (%): C, 79.19; H, 6.15; N, 6.84.
4,4,5,5ꢀTetramethylꢀ2ꢀ[4ꢀ(2,3,5,6,8,9,11,12ꢀoctahydroꢀ
1,4,7,10,13ꢀpentaoxabenzocyclopentadecenꢀ15ꢀylethynyl)pheꢀ
nyl]ꢀ2ꢀimidazolineꢀ1ꢀoxyl 3ꢀoxide (13e). The yield was 41%, m.p.
175—176 °C (from a hexane—benzene mixture). IR, ν/cm–1
:
813, 833, 907, 938, 964, 1050, 1129, 1166, 1208, 1254, 1303,

2ꢀArylꢀ2ꢀimidazolineꢀ1ꢀoxyl 3ꢀoxide
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 1, January, 2002
133
1331, 1360, 1389, 1420, 1453, 1513, 1564, 1603, 2207, 2868,
2929, 2981, 3027. ESR: aN (2 N) = 0.74 mT, aH(Me) (12 H) =
0.023 mT. Found (%): C, 66.81; H, 6.58; N, 5.13. C29H35N2O7.
Calculated (%): C, 66.52; H, 6.74; N, 5.35.
gel (2.5×1.5 cm), the solvent was distilled off in vacuo, and the
residue was crystallized from a benzene—hexane mixture. The
yield of 18 was 0.2 g (89%), with decomp. at 115—120 °C. IR,
ν/cm–1: 847, 879, 957, 1018, 1101, 1141, 1155, 1179, 1221,
1265, 1292, 1308, 1367, 1388, 1403, 1447, 1489, 1536, 1569,
1606, 2149, 2215, 2930, 2977, 3052. Found (%): C, 74.64;
H, 6.89; N, 11.45. C30H32N4O2. Calculated (%): C, 74.97;
H, 6.71; N, 11.66.
2ꢀImidazolineꢀ1ꢀoxyl (14c) was prepared from 13c analoꢀ
gously to 18, the yield was 66%, m.p. 239—241 °C (C6H6). ESR:
aN1 (1 N) = 0.91 mT, aN3 (1 N) = 0.45 mT. Found (%): C, 84.35;
H, 6.18; N, 5.94. C33H29N2O. Calculated (%): C, 84.40;
H, 6.22; N, 5.97.
2ꢀ[4ꢀ(2,3,5,6,8,9,11,12,14,15ꢀDecahydroꢀ1,4,7,10,13,16ꢀ
hexaoxabenzocyclooctadecenꢀ18ꢀylethynyl)phenyl]ꢀ4,4,5,5ꢀ
tetramethylꢀ2ꢀimidazolineꢀ1ꢀoxyl 3ꢀoxide (13f). The yield was
39%, m.p. 134—136 °C (from a hexane—benzene mixture). IR,
ν/cm–1: 810, 839, 949, 982, 1054, 1123, 1218, 1254, 1302, 1329,
1360, 1390, 1420, 1451, 1513, 1595, 2206, 2870, 2924, 3032.
ESR: aN (2 N) = 0.74 mT, aH(Me) (12 H) = 0.024 mT.
MS, m/z (Irel (%)): 567.2 [M]+ (1.63), 537.3 (5.56), 536.3
(13.32), 521.3 (6.84), 509.2 (3.38), 481.2 (5.76), 480.1 (33.0),
479.1 (100.0), 438.1 (6.05), 437.1 (24.46), 339.1 (6.28), 303.1
(3.10), 262.0 (14.52), 261.0 (43.24), 247.0 (4.0), 246.0 (10.86),
235.0 (4.48), 234.0 (4.18), 206.0 (5.78), 204.9 (10.09), 177.0
(7.79), 163.0 (8.21), 152.0 (3.24), 114.1 (8.10), 98.1 (9.10),
89.0 (5.31), 84.1 (65.54). Highꢀresolution mass spectrum.
Found: m/z 567.27100 [M]+. C31H39N2O8. Calculated: M =
567.27062.
2ꢀ[3ꢀ(Biphenylꢀ4ꢀylethynyl)phenyl]ꢀ4,4,5,5ꢀtetramethylꢀ2ꢀ
imidazolineꢀ1ꢀoxyl 3ꢀoxide (12b) was prepared analogously to
13c, except that the synthesis was carried out at 35—40 °C
and a 1 : 10 Et3N—Py mixture was used instead of piperiꢀ
dine. The yield was 79%, m.p. 161—163 °C (from a hexꢀ
ane—benzene mixture). IR, ν/cm–1: 815, 837, 1000, 1019,
1065, 1103, 1129, 1166, 1214, 1302, 1363, 1388, 1423, 1449,
1485, 1526, 1600, 2213, 2928, 2987, 3032. ESR: aN (2 N) =
0.73 mT, aH(Me) (12 H) = 0.024 mT. Found (%): C, 79.43;
H, 6.03; N, 6.58. C27H25N2O2. Calculated (%): C, 79.19;
H, 6.15; N, 6.84.
We thank V. I. Ovcharenko and S. V. Fokin for valuꢀ
able advice and help in the work.
This study was financially supported by the Russian
Foundation for Basic Research (Project No. 98ꢀ03ꢀ32908a),
by the Ministry of Education of the Russian Federation
(Grant in Fundamental Natural Sciences, 1998), by the US
Civilian Research and Development Foundation (Grant
Recꢀ008), and by the Siberian Branch of the Russian Acadꢀ
emy of Sciences (Integration Grant 12 and Grant for Young
Scientists). The IR and NMR spectroscopic and mass specꢀ
trometric studies were carried out in the Joint Use Anaꢀ
lytical Center (N. N. Vorozhtsov Institute of Organic
Chemistry, Siberian Branch of the Russian Academy of
Sciences) and were financially supported by the Rusꢀ
sian Foundation for Basic Research (Project No. 00ꢀ03ꢀ
40135).
Compounds 12c,d were prepared analogously to 12b.
4,4,5,5ꢀTetramethylꢀ2ꢀ[3ꢀ([1,1´;4´,1″]terphenylꢀ4ꢀylꢀ
ethynyl)phenyl]ꢀ2ꢀimidazolineꢀ1ꢀoxyl 3ꢀoxide (12c). A mixture
of 4ꢀiodoterphenyl 1c (0.42 g, 1.2 mmol), Pd[PPh3]2Cl2 (40 mg,
0.057 mmol), CuI (20 mg, 0.11 mmol), Et3N (1 mL), and Py (or
Et3N) (10 mL) was stirred under a stream of argon at 35—40 °C
for 30 min. Then 2ꢀimidazolineꢀ1ꢀoxyl 3ꢀoxide 11b (0.33 g, 1.3
mmol) was added and the reaction mixture was stirred for 2 h.
The reaction product was isolated analogously to 13c. The yield
of nitroxyl 12c was 66%, m.p. 226—228 °C (from benzene). IR,
ν/cm–1: 827, 865, 908, 1002, 1078, 1138, 1166, 1217, 1272,
1304, 1364, 1389, 1420, 1450, 1485, 1506, 1593, 2207, 2989,
3033. ESR: aN (2 N) = 0.73 mT, aH(Me) (12 H) = 0.021 mT.
Found (%): C, 81.35; H, 6.18; N, 5.64. C33H29N2O2. Calcuꢀ
lated (%): C, 81.62; H, 6.02; N, 5.77.
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Received December 9, 2000;
in revised form June 19, 2001