ORGANIC
LETTERS
2013
Vol. 15, No. 4
824–827
Rh2(II)-Catalyzed Selective Aminomethylene
Migration from Styryl Azides
Chen Kong, Navendu Jana, and Tom G. Driver*
Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street,
Chicago, Illinois, 60607-7061, United States
Received December 20, 2012
ABSTRACT
Rh2(II)-Carboxylate complexes were discovered to promote the selective migration of aminomethylenes in β,β-disubstituted styryl azides to form
2,3-disubstituted indoles. Mechanistic data are also presented that suggest that the migration occurs stepwise before diffusion of the iminium ion.
The formation of new carbonÀcarbon bonds through
transition metal-catalyzed migration reactions continues
to be pursued by researchers because it rapidly transforms
simple starting materials into complex, functionalized
products.1 While metal-catalyzed carbene reactions are
well established to induce 1,2-shifts from the resulting
oxonium2À4 or ammonium ylide,5 triggering these migra-
torial processes with the analogous N-atom transfer
remains significantly underdeveloped.6 We have pursued
using aryl azides in Rh2(II)-catalyzed CÀH bond amina-
tion reactions,7,8 and our mechanistic experiments sug-
gested that CÀN bond formation occurred through a
4π-electron-5-atom electrocyclization.9 We exploited this
mechanism to induce selective 1,2-shifts ofβ-substituents10
and discovered that aryl group migration could be triggered
from β,β-disubstituted styryl azides such as 1 to afford
2-alkyl-3-aryl indoles as the only product (Scheme 1).10a,11
The identities of the two β-substituents in these substrates,
however, differed considerably, and we were curious if
our migratorial process could distinguish between two
β-methylene units if one was substituted with an amine.
Despite the well-established use of heteroatoms as
(1) For recent reviews, see: (a) Nicolaou, K. C.; Edmonds, D. J.;
Bulger, P. G. Angew. Chem., Int. Ed. 2006, 45, 7134. (b) Padwa, A.; Bur,
S. K. Tetrahedron 2007, 63, 5341. (c) Nicolaou, K. C.; Chen, J. S. Chem.
Soc. Rev. 2009, 38, 2993. (d) Grant, T. N.; Rieder, C. J.; West, F. G.
Chem. Commun. 2009, 5676.
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Rev. 1991, 91, 263. (b) Ye, T.; McKervey, M. A. Chem. Rev. 1994, 94,
1091. (c) Nitrogen, Oxygen and Sulfur Ylide Chemistry: Practical Ap-
proach in Chemistry; Clark, J. S., Ed.; Oxford University Press: Oxford,
2002; Chapter 1, pp 1À98.
(6) For notable exceptions, see: (a) Thornton, A. R.; Blakey, S. B.
J. Am. Chem. Soc. 2008, 130, 5020. (b) Thornton, A. R.; Martin, V. I.;
Blakey, S. B. J. Am. Chem. Soc. 2009, 131, 2434.
(3) For seminal reports, see: (a) Nozaki, H.; Takaya, H.; Moriuti, S.;
Noyori, R. Tetrahedron 1968, 24, 3655. (b) Kirmse, W.; Chiem, P. V.;
Schurig, V. Tetrahedron Lett. 1985, 26, 197. (c) Roskamp, E. J.; Johnson,
C. R. J. Am. Chem. Soc. 1986, 108, 6062. (d) West, F. G.; Naidu, B. N;
Tester, R. W. J. Org. Chem. 1994, 59, 6892. (e) West, F. G.; Naidu, B. N.
J. Am. Chem. Soc. 1994, 116, 8420. (f) Clark, J. S.; Fretwell, M.;
Whitlock, G. A.; Burns, C.; Fox, D. N. A. Tetrahedron Lett. 1998, 39,
97. (g) Doyle, M. P.; Ene, D. G.; Forbes, D. C.; Tedrow, J. S. Tetra-
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(7) Cf.: (a) Stokes, B. J.; Dong, H.; Leslie, B. E.; Pumphrey, A. L.;
Driver, T. G. J. Am. Chem. Soc. 2007, 129, 7500. (b) Shen, M.; Leslie,
B. E.; Driver, T. G. Angew. Chem., Int. Ed. 2008, 47, 5056. (c) Nguyen,
Q.; Sun, K.; Driver, T. G. J. Am. Chem. Soc. 2012, 134, 7262.
(8) For recent reviews of the use of azides in metal-catalyzed N-atom
transfer reactions, see: (a) Katsuki, T. Chem. Lett. 2005, 34, 1304. (b)
Cenini, S.; Gallo, E.; Caselli, A.; Ragaini, F.; Fantauzzi, S.; Piangiolino,
C. Coord. Chem. Rev. 2006, 250, 1234. (c) Driver, T. G. Org. Biomol.
Chem. 2010, 8, 3831. (d) Jenkins, D. M. Synlett 2012, 23, 1267.
(9) Stokes, B. J.; Richert, K. J.; Driver, T. G. J. Org. Chem. 2009, 74,
6442.
(10) (a) Sun, K.; Liu, S.; Bec, P. M.; Driver, T. G. Angew. Chem., Int.
Ed. 2011, 50, 1702. (b) Stokes, B. J.; Liu, S.; Driver, T. G. J. Am. Chem.
Soc. 2011, 133, 4702.
(11) For leading reports of related aryl 1,2-shifts triggered by Nazarov
electrocyclizations, see: (a) Huang, J.; Lebuf, D.; Frontier, A. J. J. Am.
Chem. Soc. 2011, 133, 6307. (b) Lebuf, D.; Gandon, V.; Ciesielski, J.;
Frontier, A. J. J. Am. Chem. Soc. 2012, 134, 6296.
(4) For leading reports, see: (a) Pirrung, M. C.; Brown, W. L.; Rege,
€
S.; Laughton, P. J. Am. Chem. Soc. 1991, 113, 8561. (b) Marmsater,
F. P.; Murphy, G. K.; West, F. G. J. Am. Chem. Soc. 2003, 125, 14724.
€
(c) Marmsater, F.; Vanecko, J. A.; West, F. G. Org. Lett. 2004, 6, 1657.
(d) Murphy, G. K.; West, F. G. Org. Lett. 2005, 7, 1801. (e) Jaber, D. M.;
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(5) (a) West, F. G.; Naidu, B. N. J. Am. Chem. Soc. 1994, 116, 8420.
(b) Glaeske, K. W.; West, F. G. Org. Lett. 1999, 1, 31. (c) Vanecko, J. A.;
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r
10.1021/ol400137q
Published on Web 02/04/2013
2013 American Chemical Society