New method of synthesis of 2-arylindoles and naphtho[1,2-d]imidazoles

Full text of DOI:10.1134/S1070428013080277

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 8, pp. 1244−1245. © Pleiades Publishing, Ltd., 2013.
Original English Text © A.S. Lyakhovnenko, T.S. Red’ko, I.V. Aksenova, N.A. Aksenov, A.V. Aksenov, 2013, published in Zhurnal Organicheskoi Khimii, 2013,
Vol. 49, No. 8, pp. 1257−1258.
SHORT
COMMUNICATIONS
New Method of Synthesis of 2-Arylindoles
and Naphtho[1,2-d]imidazoles
A. S. Lyakhovnenko, T. S. Red’ko, I. V. Aksenova, N. A. Aksenov, and A. V. Aksenov
North-Caucasian Federal University, Stavropol’, 355009 Russia
e-mail: k-biochem-org@stavsu.ru
Received December 5, 2012
DOI: 10.1134/S1070428013080277
One of the most important tasks of the chemists is the
search for new reagents and development of new synthetic
methods. The methods that do not require a preliminary
functionalization of initial compounds are especially
interesting. Indoles are well known substances whose
preparation methods are numerous, for instance [1, 2]. Yet
up till now no methods are known involving the formation
of N1–C7a and С3–C3a bonds. We suggest such method in
this report based on recently found reagents combination
NaN3–polyphosphoric acid (PPA)1 [4].
The reaction of anisole (I) with NaN3 in PPA at
55–60°С within 3 h followed by the addition of phenacyl
bromides IIа–IIc and subsequent heating for 4 h more
at 120–130°С resulted in indoles IIIа–IIIc in 18–26%
O
Br
X
O
MeO
MeO
IIа_IIc
NaN3
PPA
H
O...
P
N
N
N
OMe
X
_N2, _H3PO4, _HBr
N
H
OH
I
IIIа_IIIc
X = H (a), Me (b), ОМе (c).
yields. With phenol only tars were obtained.
We selected as model target compounds naphtho[1,2-d]
imidazoles Vа–Vc. Although these compounds are well
known, the existing synthetic methods have a significant
disadvantage of using 2-naphthylamine as the initial com-
pound [5–8]. We suggest in this study a method lacking
Next we demonstrated the efficiency of the found
reagents system in combination with the other reactions,
in particular, in the succession of the Schmidt reaction,
in the electrophilic amination, in the heterocyclization.
O
R
O
R
O
N
_N2
_H3PO4
NH
NaN3
PPA
R
NaN3
PPA
H
...O P
HO
N
N
N
HN
IVа_IVc
HN
O
R
Vа_Vc
R = Me (а), Ph (b), Bn (c).
_________________
1 PPAused contained 86% of P2O5 and was synthesized by method [3].
1244

NEW METHOD OF SYNTHESIS OF 2-ARYLINDOLES
1245
this disadvantage. The reaction of 2-acetylnaphthalene
(IVа) with 3-fold excess of NaN3 in polyphosphoric
acid at 80–90°С (6 h) followed by 3 h at 120–130°С
affords 2-methylnaphtho[1,2-d]-imidazole (Vа) in a
47% yield.
0.086 g (47%), mp 170–171oC (benzene) (mp 168–169°C
[5], 172°C [6]). 1Н NMR spectrum is analogous to that
published in [6].
2-Phenylnaphtho[1,2-d]imidazole (Vb). Yield 0.127
g (52%), mp 221–222°C (benzene) (mp 221.5–222°C
1
The reaction proceeds similarly with 2-phenacetyl-
[7]). Н NMR spectrum is analogous to that published
and 2-benzoylnaphthalene (IVb, IVc).
in [7].
2-Arylindoles IIIа–IIIc. A mixture of 0.108 g
(1 mmol) of anisole (I) and 0.072 g (1.1 mmol) of NaN3
in 2–3 g of PPAwas vigorously stirred for 3 h at 55–60°С
(TLC monitoring). Then the temperature was raised
to 120–130°С, and the stirring was continued for 1 h
more, then 1 mmol of the appropriate phenacyl bromide
IIа–IIc was added, and the stirring at this temperature
was continued for 4 h more. The reaction mixture was
cooled, poured at stirring into 30 ml of cold water, the
solution was alkalinized with ammonia solution, and
extracted with ethyl acetate (5 × 50 ml). The solution was
evaporated, the residue was subjected to chromatographic
separation, eluent benzene.
2-Benzylnaphtho[1,2-d]imidazole (Vc). Yield 0.098
g
(38%), mp 185–186oC (benzene) (mp 185–186°C [8]).
1Н NMR spectrum is analogous to that published in [8].
NMR spectra were registered on a spectrometer
Bruker WP-200 (200 МHz), internal reference TMS. The
reaction progress was monitored and the homogeneity
of the synthesized compounds was checked by TLC on
Silufol UV-254 plates, eluent benzene.
ACKNOWLEDGMENTS
The study was carried out under the financial support
of the Russian Foundation for Basic Research (grant no.
12-03-31646 mol_а).
6-Methoxy-2-phenylindole (IIIa). Yield 0.058 g
(26%), mp 168–169°C (benzene–petroleum ether) (mp
168–169°C [2]).
REFERENCES
6-Methoxy-2-(4-tolyl)indole (IIIb). Yield 0.057 g
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188–189°C [2]).
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1Н NMR spectra of 2-arylindoles are analogous to
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1 mmol of ketone IVа–IVc and 0.195 g (3 mmol) of
NaN3 in 2–3 g of PPA was vigorously stirred for 6 h at
80–90°С (TLC monitoring). Then the temperature was
raised to 120–130°С, and the stirring was continued for
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2-Methylnaphtho[1,2-d]imidazole (Va). Yield
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