3
Ph
present method requires only two-steps starting from
commercially available 1,2-diphenylethanones.
Ph
Ph
Te
Ph
Ph
DBU
TeCl
NNH2
+
+
Te
4
Te
DMF
reflux
12h
1m
In summary, we have synthesized 2,5-disubstituted
tellurophenes from easily available ketone hydrazones and
TeCl4. Benzotellurophenes are also formed by the reaction of
1,2-diphenylethanone hydrazones with TeCl4 in the presence
of DBU. By applying intramolecular sigmatropic reaction
followed by oxidation, a novel type of tellurophene synthesis
was provided. Further application of this methodology is
currently under investigation.
3b
2b
Ph
Ph
Ph
Ph
Te
DBU
Ph
TeCl
NNH2
+
4
Te
+
DMF
reflux
12h
Te
2c
1n
3c
Scheme 4. Reaction of propiophenone or isobutyro-
phenone with TeCl4
Interestingly,
1,2-diphenylethanone
(dihydrobenzoin)
hydrazone 1o reacted with TeCl4 to afford benzotellurophene
5a in 45% yield along with trans-stilbene (25%). Similarly,
substituted benzotellurophenes 5b and 5c were obtained in
39% and 43% yields along with stilbene 6b (5%) and 6c
(15%), respectively (Scheme 5).
References
1
For reviews, Thiophene: E. T. Pelkey, Prog. Hetererocyclic Chem.,
1998, 10, 87-108. Selenophene: Chem. Heterocyclic Compd. 2000,
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Chem., 2011, 9, 1301-1313. E. Rivard, Chem. Lett. 2015, 44, 730-
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Ar
Te
DBU
+
NNH2
Ar
TeCl4
DMF
reflux
18h
PhCH2
5a: Ar= Ph
1o: Ar= Ph
1p: Ar= p-MeC6H4
1q: Ar= p-ClC6H4
5b: Ar= p-MeC6H4
5c: Ar= p-ClC6H4
Ar
+
Ph
6a: Ar= Ph
6b: Ar= p-MeC6H4
6c: Ar= p-ClC6H4
2
a) C. R. B. Rhode, G. Zeni, Org. Biomol. Chem., 2011, 9, 1301-
1313. G. E. Garrett, E. I. Carrera, D. S. Seferos, M. S. Taylor,
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Howe, D. S. Seferos, Angew. Chem. Int. Ed. 2010, 49, 10140-
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Scheme 5. Synthesis of benzotellurophenes
3
4
E. H. Braye, W. Hubel, I. Caplier, J. Am. Chem. Soc., 1961, 83,
4406-4413.
W. Mack, Angew. Chem. Int. Ed. 1966, 5, 896. T. M. McCormick,
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Initially formed telluroketone reacted with TeCl4 to afford
tellurium ion D, intramolecular aromatic substitution gave
benzotellurophene 5 (Scheme 6). It is well known that
diazoalkanes were formed as intermediates for this type of
reaction,9 thus, trans-stilbene might be formed via
diazoalkane intermediate.
5
6
M. J. Dabdoub, V. B. Dabdoub, P. G. Guerrero Jr. Tetrahedron,
1997, 53, 4199-4218.)
a) G. He, L.Kang, W. Torres Delgado, O. Shynkaruk, M. J.
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K. Okuma, S. Yahata,, K. Kage, K. Munakata, N. Nagahora, K.
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898.
Ph
Ph
Ph
TeCl4
DBU
Te
NNH2
Te
PhCH2
PhCH2
H
PhHC
7
Ph
Ph
TeCl3
DBU
TeCl4
DBU
Te
Te
8
9
M. Katkevics, S. Yamaguchi, A.Toshimitsu, K.Tamao,
Organometallics, 1998, 17, 5796-5800.
HC
HC
H
TeCl3
DBUH Cl
a) M. Minoura, T. Kawashima, R. Okazaki, J. Am. Chem. Soc.
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D
Te
Ph
DBUHTeCl3
10
5a
Scheme 6. The mechanism of formation of
benzotellurophene 5
.
Previously, benzotellurophenes are generally synthesized
via four-step procedure from o-(methyltelluro)benzaldehyde
or o-bromethylbenzene and t-BuLi and tellurium.10
The