Organic Letters
Letter
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At this stage, we unfortunately have not clarified the reason
why ethylbenzene was not formed from Rh(III) complex 9. Our
present speculation is that the reaction rate from 9 to 10 might be
fast enough in this reaction.
To expand the synthetic utility, a homocoupling product was
applied to the synthesis of imipramine. Imipramine is one of the
earliest drugs used as a tricyclic antidepressant (TCA), and it has
also been used to treat nocturnal enuresis.17 There are many
reports for the synthesis of imipramine and its analogues to date,
but most of syntheses were carried out using dibenzo[b,f]-
azepines as the starting material. Consequently, there is a
demand for other pathways for synthesizing imipramine and its
analogues. Recently, some groups reported a new approach for
ring-closure reactions by using Buchwald−Hartwig amination.18
We applied the amination to 6d to give imipramine (13) in good
yield (Scheme 4).
Scheme 4. Synthesis for Imipramine Using Pd-Catalyzed
Double Amination
In conclusion, we have developed a novel Rh-catalyzed
homocoupling reaction and proposed a reaction mechanism.
Our reaction proceeds under very mild conditions and can be
applied to various substrates which have sensitive substituents.
To the best of our knowledge, this kind of reaction using an Rh
catalyst for a Csp3−Csp3 coupling reaction has not been
reported. Furthermore, we provided a new approach to
imipramine from a homocoupling product. This means that
various types of imipramine derivatives would be accomplished
by a synthesis using the corresponding 1,2-bis(2-bromophenyl)-
ethanes derived from our homocoupling reaction. The reaction
could be applied to the synthesis of various dibenzylic products,
and we hope for further expansion to other fields.
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ASSOCIATED CONTENT
* Supporting Information
■
S
Experimental details and characterization of the compounds.
This material is available free of charge via the Internet at http://
AUTHOR INFORMATION
Corresponding Author
Akssira, M.; Hanbali, F. E.; Arteaga, J. F.; Dieg
J. Org. Chem. 2007, 72, 2251−2254.
́ ́
uez, H. R.; Sanchez, E. M.
■
(13) (a) Duan, X.-J.; Li, X.-M.; Wang, B.-G. J. Nat. Prod. 2007, 70,
1210−1213. (b) Oh, K.-B.; Jeon, H. B.; Han, Y.-R.; Lee, Y.-J.; Park, J.;
Lee, S.-H.; Yang, D.; Kwon, M.; Shin, J.; Lee, H.-S. Bioorg. Med. Chem.
Lett. 2010, 20, 6644−6648. (c) Barrett, T. N.; Braddock, D. C.; Monta,
A.; Webb, M. R.; White, A. J. P. J. Nat. Prod. 2011, 74, 1980−1984.
(d) Liu, M.; Hansen, P. E.; Lin, X. Mar. Drugs 2011, 9, 1273−1292.
(14) (a) Ryu, I.; Araki, F.; Minakata, S.; Komatsu, M. Tetrahedron Lett.
1998, 39, 6335−6336. (b) Bertrand, M. P.; Feray, L.; Nouguier, R.;
Perfetti, P. J. Org. Chem. 1999, 64, 9189−9193. (c) Bertrand, M. P.;
Coantic, S.; Feray, L.; Nouguier, R.; Perfetti, P. Tetrahedron 2000, 56,
3951−3961. (d) Yamada, K.; Fujihara, H.; Yamamoto, Y.; Miwa, Y.;
Taga, T.; Tomioka, K. Org. Lett. 2002, 4, 3509−3511. (e) Akindele, T.;
Yamada, K.; Tomioka, K. Acc. Chem. Res. 2009, 42, 345−355. (f) Maury,
J.; Jammi, S.; Vibert, F.; Marque, S. R. A.; Siri, D.; Feray, L.; Bertrand, M.
J. Org. Chem. 2012, 77, 9081−9086.
Notes
The authors declare no competing financial interest.
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