ISSN 1070-4280, Russian Journal of Organic Chemistry, 2010, Vol. 46, No. 3, pp. 457–458. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © E.Yu. Shmidt, N.V. Zorina, A.I. Mikhaleva, I.A. Ushakov, E.V. Skital’tseva, B.A. Trofimov, 2010, published in Zhurnal
Organicheskoi Khimii, 2010, Vol. 46, No. 3, pp. 461–462.
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1,3,5-Triphenylbenzene as Unexpected By-Product
in the Synthesis of 2,5-Diphenylpyrrole from Acetophenone
Oxime and Phenylacetylene
E. Yu. Shmidt, N. V. Zorina, A. I. Mikhaleva, I. A. Ushakov,
E. V. Skital’tseva, and B. A. Trofimov
Favorskii Irkutsk Institute of Chemistry, Siberian Division, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
e-mail: boris_trofimov@irioch.irk.ru
Received May 6, 2009
DOI: 10.1134/S1070428010030292
Despite poor yield of the target product (25%), the
reaction of acetophenone oxime (I) with phenylacety-
lene (II) in superbasic medium (Trofimov reaction)
[1–4], leading to 2,5-diphenyl-1H-pyrrole (III), attracts
interest from the preparative viewpoint, for alternative
methods include a number of steps [5], and the overall
yield (calculated with account taken of all steps) is
comparable to that in the Trofimov synthesis. Deter-
mination of structure of by-products in the reaction of
oxime I with acetylene II may be useful for under-
standing its mechanism and further optimization to
enhance its preparative efficiency.
However, this assumption was not confirmed experi-
mentally. We also found that under the given condi-
tions compound V cannot be formed as a result of
autocondensation of oxime I or ketone IV. Presum-
ably, O-vinyl oxime VI which is the primary interme-
diate in the synthesis of pyrroles from ketone oximes
and acetylene [6] (Scheme 2) undergoes rearrangement
into nitrone VII (as reported in [7] for cyclohexanone
oxime O-allyl ether). Enhanced CH acidity of the CH3
group in VII due to strong electron-withdrawing effect
of the N-oxide fragment favors aldolization (crotoniza-
tion) of VII with acetophenone IV. The condensation
of azatriene VIII thus formed with the second aceto-
phenone molecule gives azatetraene IX, and cycliza-
tion of the latter, followed by aromatization of dihy-
drobenzene X via elimination of vinylnitrone XI,
yields triphenylbenzene V. Compound XI can be con-
verted into acetophenone oxime (I).
We were the first to isolate from the product mix-
ture (LiOH–DMSO, 130°C, 5 h) 6% of 1,3,5-tri-
phenylbenzene (V) together with pyrrole III and aceto-
phenone IV (deoximation product of initial oxime I)
(Scheme 1).
Scheme 1.
The revealed reaction essentially extends the exist-
ing views on processes accompanying the synthesis of
pyrroles from ketone oximes and acetylenes [1, 6], and
it should be taken into account while optimizing the
synthesis of 2,5-diphenyl-1H-pyrrole (III) according to
Scheme 1. Moreover, special study on this reaction
could lead to development of a preparative procedure
for the synthesis of 1,3,5-triarylbenzenes.
LiOH–DMSO
130°C, 5 h
NOH
+
Ph
CH
Ph
Ph
N
H
Ph
Me
I
II
III
Ph
O
+
+
1,3,5-Triphenylbenzene (V). Phenylacetylene,
3.78 g (37 mmol), was added to a mixture of 5.00 g
(37 mmol) of acetophenone oxime (I) and 0.89 g
(37 mmol) of lithium hydroxide in 40 ml of dimethyl
sulfoxide, and the mixture was heated for 5 h at 130°C.
Ph
Me
Ph
Ph
IV
V
It could be presumed that 1,3,5-triphenylbenzene
(V) is formed via trimerization of phenylacetylene.
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