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Organic & Biomolecular Chemistry
2000, 7, 37; (c) G. W. Gribble, Chem. Soc. Rev., 1999, 28, 335; (d)
G. W. Gribble, Acc. Chem. Res., 1998, 31, 141; (e) M. Alvarez, M.
Salas and J. A. Joule, Heterocycles, 1991, 32, 1391; The synthesis of
bromoindoles is usually performed by the direct bromination of
indoles using bromine, pyridinium tribromide, N-bromosuccinimide,
etc., but the yields or the selectivity are not satisfactory in general.
A potentially promising subset of the spirooxindole alkaloids are the
oxa-spirooxindoles, joining two privileged motifs, the oxacycle and
spirooxindole substructures. For reviews, see: (a) J. J. Badillo, N. V.
Hanhan and A. K. Franz, Curr. Opin. Drug. Disc., 2010, 13, 758; (b)
B. M. Trost and M. K. Brennan, Synthesis, 2009, 3003; (c) C. Marti,
and E. M. Carreira, Eur. J. Org. Chem., 2003, 2209; For a recent
selected example, see: (d) S. Ouyang, L. Wang, Q.-W. Zhang, G.-C.
Wang, Y. Wang, X.-J. Huang, X.-Q. Zhang, R.-W. Jiang, X.-S. Yao,
C.-T. Che, and W.-C. Ye, Tetrahedron, 2011, 67, 4807.
compound 3a (26 mg, 95%) as a colorless oil.
Spirocyclic 5-Bromooxindole 18. From 18 mg (0.052 mmol) of
spirocyclic iododihydrofuran 4a, and after chromatography of the
residue using hexanes/ethyl acetate (2:1) as eluent gave
compound 18 (14 mg, 66%) as a yellow oil; 1H-NMR (700 MHz,
65
70
75
5
8
o
CDCl3, 25 C) δ: 7.47 (dd, J = 8.2, 1.8 Hz, 1H), 7.30 (d, J = 2.1
Hz, 1H), 6.72 (d, J = 2.1, 1H), 4.98 and 4.87 (m, each 1H), 3.18
(s, 3H), 1.47 (t, J = 2.1 Hz, 3H); 13C-NMR (175 MHz, CDCl3, 25
oC) δ: 173.7, 142.8, 138.7, 133.3, 129.3, 127.8, 124.6, 115.9,
10 109.9, 89.2, 82.7, 26.4, 13.0; IR (CHCl3, cm–1): ν 1714; HRMS
(ES): calcd for C13H12BrINO2[M + H]+: 419.9096; found:
419.9075.
9
For the pioneered Au-catalyzed cycloisomerization of α-allenols, see:
(a) A. Hoffmann-Röder and N. Krause, Org. Lett., 2001, 3, 2537; (b)
M. Asikainen and N. Krause, Adv. Synth. Catal., 2009, 351, 2305.
Acknowledgments
80 10. For the gold-catalyzed 5-endo cyclization of α-allenols in the
presence of N-iodosuccinimide to afford iodinated dihydrofurans,
see: (a) M. Poonoth and N. Krause, Adv. Synth. Catal., 2009, 351,
117; For the gold-catalyzed 6-endo cyclization of β-allenols in the
presence of N-iodosuccinimide to afford iodinated dihydropyrans,
Support for this work by the DGI-MICINN (Project CTQ2009-
15 09318) and Comunidad Autónoma de Madrid (Project
S2009/PPQ-1752) are gratefully acknowledged. N. P. thanks
CSIC and MEC for studentships (JAE-intro and beca de
colaboración).
85
90
95
see: (b) B. Gockel and N. Krause, Eur. J. Org. Chem., 2010, 311; For
detailed studies of C–halogen bond formation from organogold
intermediates, see: (c) A. S. K. Hashmi, T. D. Ramamurthi and F.
Rominger, J. Organomet. Chem., 2009, 694. 592; (d) A. S. K.
Hashmi, T. D. Ramamurthi, M. H. Todd, A. S.-K. Tsang and K. Graf,
Aust. J. Chem., 2010, 63, 1619.
Notes and references
20 a Grupo de Lactamas y Heterociclos Bioactivos, Departamento de
Química Orgánica I, Unidad Asociada al CSIC, Facultad de Química,
Universidad Complutense de Madrid, 28040-Madrid, Spain. Fax: +34-
91-3944103 E-mail:alcaideb@quim.ucm.es
11. The reaction of arenes with electrophiles is a conceptually powerful
method to functionalize C–H bonds. However, the halogenation of
arenes proceeds only in the presence of strong acids under harsh
conditions. After the initiation of our efforts, two reports appeared
describing the gold-catalyzed halogenation of arenes by N-
bromosuccinimide, see: (a) F. Mo, J. M. Yan, D. Qiu, F. Li, Y.
Zhang and J. Wang, Angew. Chem. Int. Ed., 2010, 49, 2028; (b) A. S.
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b Instituto de Química Orgánica General, IQOG, Consejo Superior de
25 Investigaciones Científicas (CSIC), Juan de la Cierva 3, 28006-Madrid,
Spain. Fax: +34-91-5644853 E-mail: Palmendros@iqog.csic.es
† Electronic Supplementary Information (ESI) available: Copies of the 1H
NMR and 13C NMR spectra for all new compounds. See
30 DOI: 10.1039/b000000x/
100 12. Starting allenols, were prepared using our methodology: B. Alcaide,
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3198.
1
For a selected review, see: Metal-Catalyzed Cross-Coupling
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2
For selected reviews, see: (a) Modern Gold Catalyzed Synthesis, eds.
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B. Alcaide, P. Almendros and J. M. Alonso, Org. Biomol. Chem.,
2011, 9, 4405; (f) A. Corma, A. Leyva-Pérez and M. J. Sabater,
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17. The fact that other metal ions were not effective for the arene
bromination/spirocyclization sequence would ruled out the
hypothesis of simple Lewis acid catalysis, with the gold salt
activating the brominating reagent.
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35
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3
4
For selected reviews, see: (a) A. S. Eustáquio, D. O’Hagan and B. S.
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(a) B. Alcaide, P. Almendros, J. M. Alonso and I. Fernández, Chem.
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5
6
7
Bromoindole alkaloids have been isolated as the secondary
metabolites of marine organisms, such as sponges, tunicates, etc., and
are promising sources of new biologically active molecules. For
selected reviews, see: (a) G. W. Gribble, Prog. Chem. Org. Nat.
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