FORMATION OF POLYAROMATIC COMPOUNDS
1357
Scheme 2.
Ar
Ar'
Ar
Pd(OAc)2, DMF
NBu3, 80°C
Ar'
Ar
H
Ar
CH
+
Ar'I
Ar
Ar'
+
+
+
Ar
Ar
Ar'
Ar
Ar
Ar
1, 7–28%
2, 6–14%
3, traces
4, 10–21%
Ar
Ar
Ar
Ar'
Ar'
Ar'
Ar'
Ar
Ar
+
+
+
+
Ar
Ar
Ar
Ar
Ar
Ar
Ar
8, traces
5, 21–35%
6, 10–14%
7, 1–3%
1, Ar = Ar′ = Ph; 2, Ar = Ph, Ar′ = 4-MeC6H4; 3, Ar = Ph, Ar′ = 4-MeOC6H4; 4, Ar = Ph, Ar′ = 4-MeC(O)C6H4; 5, Ar = 4-MeC6H4,
Ar′ = Ph; 6, Ar = 4-MeOC6H4, Ar′ = Ph; 7, Ar = 4-MeC(O)C6H4, Ar′ = Ph; 8, Ar = 4-MeC6H4, Ar′ = 4-MeOC6H4.
Sonogashira by-products in the two-component system
aryl halide–acetylene in the absence of Cu(I) [9], as
well as by studying model stoichiometric reactions
[10]. In this case, enynes were formed according to the
following reaction sequence: oxidative addition (a),
carbopalladation (c), and nucleophilic substitution (f),
where acetylide ion acted as nucleophile in the final
step (Scheme 1).
Coupling of aryl iodides with arylacetylenes
(general procedure). The reactions were carried out at
80°C in a reactor equipped with a rubber septum and
magnetic stirrer (477.5 rpm) by mixing 5 mL DMF,
5 mmol of aryl iodide, 10 mmol of arylacetylene,
0.08 mmol of Pd(OAc)2, 1 mmol of naphthalene
(internal standard), and 6.5 mmol of tributylamine
(base). Samples were withdrawn intermittently and
analyzed by GC/MS; the yields were determined by
the internal standard technique.
We were the first to obtain experimental evidences
for the third path including successive carbopallada-
tion of the second and third acetylene molecules
(Scheme 1, d). In the reactions of aryl iodides with
excess arylacetylenes (Scheme 2; 8 examples), apart
from small amounts of the corresponding diarylacety-
lene 1 (Sonogashira product) and enyne 2 (observed
previously), we detected tetraarylbenzenes 3–5 and
tetraarylfulvenes 6–8. Tetraarylfulvenes 6–8 were
formed via Markovnikov carbopalladation of the first
arylacetylene molecule, so that the product possessed
no β-hydrogen atom necessary for elimination of
palladium and closure of benzene ring after successive
carbopalladation of two more arylacetylene molecules.
The cyclization to six-membered ring with formation
of tetraarylbenzenes is possible only in the case of
anti-Markovnikov carbopalladation of the first aryl-
acetylene molecule. The presence of three regioiso-
meric tetraarylbenzenes 3–5 and three regioisomeric
tetraarylfulvenes 6–8 in the reaction mixture indicates
different regioselectivities in the carbopalladation of
the second and third arylacetylene molecules. Thus,
two-component reactions of organic halides with
acetylenes may form the basis of a new family of
two- and three-component couplings with various
nucleophiles.
Gas chromatographic–mass spectrometric analysis
was performed on a Shimadzu QP 2010 Ultra instru-
ment equipped with a GsBP-5MS column (0.25 mm×
30 m, film thickness 0.25 μm); carrier gas helium,
oven temperature programming from 100 to 250°C;
total ion monitoring in the a.m.u. range 15–900
(integer values) at a rate of 5000 a.m.u./s. The products
were identified by comparing their mass spectra with
those included in Wiley, NIST, and NIST05 MS
libraries and of authentic samples (Aldrich).
This study was performed in the framework of the
project part of state assignment of the Ministry of
Education and Science of the Russian Federation
(contract no. 4.353.2014/K).
REFERENCES
1. Sonogashira, K., Tohda, Y., and Hagihara, N., Tetra-
hedron Lett., 1975, vol. 16, p. 4467.
2. Dieck, H.A. and Heck, R.F., J. Organomet. Chem., 1975,
vol. 93, p. 259.
3. Heck, R.F. and Nolley, J.P., J. Org. Chem., 1972, vol. 37,
p. 2320.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 52 No. 9 2016
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