N. Sadayori, U. Radhakrishnan and Y. Yamamoto, J. Am. Chem.
Soc., 1999, 121, 6391.
4 For a sequential one-pot procedure involving Sonogashira coupling and
homo-benzannulation for the synthesis of 6H-dibenzo[b,d]pyran-6-ones,
see: (a) T. Kawasaki and Y. Yamamoto, J. Org. Chem., 2002, 67, 5138;
(b) C. Xi, C. Chen, J. Lin and X. Hong, Org. Lett., 2005, 7, 347.
5 (a) M. Pal, R. Dakarapu, K. Parasuraman, V. Subramanian and
K. R. Yeleswarapu, J. Org. Chem., 2005, 70, 7179; (b) M. Pal,
K. Parasuraman, V. Subramanian, R. Dakarapu and K. R.
Yeleswarapu, Tetrahedron Lett., 2004, 45, 2305; (c) For our studies on
Cu-free Sonogashira coupling, see: M. Pal, K. Parasuraman, S. Gupta
and K. R. Yeleswarapu, Synlett, 2002, 1976.
6 For Sonogashira coupling of 2-halo-2-cyclohexenone with terminal
alkynes in the presence of Cu-salt, see: (a) T. Yao, X. Zhang and R. C.
Larock, J. Am. Chem. Soc., 2004, 126, 11164. See also:(b) M. W. Miller
and C. R. Johnson, J. Org. Chem., 1997, 62, 1582, and references cited
therein.
Scheme 2 Pd-catalyzed reactions of 1d with terminal alkyne 2a.
coupling–benzannulation of a-haloenone with terminal alkynes.
This one-pot Cu-free process was found to be general when alkyl
substituted alkynes were used affording an array of compounds of
potential biological significance,10 the preparation of which may be
tedious via other methods.
We thank Dr R. Rajagopalan, Prof. J. Iqbal, for their
encouragement and analytical group for spectral data.
7 Crystallographic data for 3b: single crystal from chloroform,
C23H30O3?CHCl3, M = 461.86, monoclinic, space group P21/c, a =
3
˚
˚
12.653(6), b = 16.148(7), c = 11.478(5) A, b = 93.125(6)u, V = 2341(1) A ,
Z = 4, Dc = 1.310 Mg m23, T = 298 K, m = 4.119 cm21, 26740
processed reflections, 5278 unique reflections, 2930 observed reflections,
Rint = 3.87%, and R = 0.090 for the 2930 ‘observed’ reflections and
wR2 = 0.167 for all 5278 unique reflections. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b612770c.
8 One of the side products isolated was identified as 2-(2,4-di-p-tolylbut-1-
en-3-ynyl)cyclohex-2-enone (see ESI{).
Notes and references
1 See, for example: (a) S. Gobbi, A. Rampa, A. Bisi, F. Belluti, P. Valenti,
A. Caputo, A. Zampiron and M. Carrara, J. Med. Chem., 2002, 45,
4931; (b) I. K. Kostakis, P. Magiatis, N. Pouli, P. Marakos, A.-L.
Skaltsounis, H. Pratsinis, S. Leonce and A. Pierre, J. Med. Chem., 2002,
45, 2599; (c) Q. Chao, L. Deng, H. Shih, L. M. Leoni, D. Genini,
D. A. Carson and H. B. Cottam, J. Med. Chem., 1999, 42, 3860; (d)
X. Wang, K. F. Bastow, C.-M. Sun, Y.-L. Lin, H.-J. Yu, M.-J. Don,
T.-S. Wu, S. Nakamura and K.-H. Lee, J. Med. Chem., 2004, 47, 5816.
2 For selected references, see: (a) V. Snieckus, Chem. Rev., 1990, 90, 879;
(b) M. Lautens, W. Klute and W. Tam, Chem. Rev., 1996, 96, 49; (c)
S. Saito and Y. Yamamoto, Chem. Rev., 2000, 100, 2901; (d)
Y. Yamamoto, J.-I. Ishii, H. Nishiyama and K. Itoh, J. Am. Chem.
Soc., 2004, 126, 3712.
9 The benzannulation may proceed via the interaction of A with the Pd(0)
species producing a p-complex intermediate B, which might act as a
nucleophilic diene and undergo (formal) Diels–Alder reaction.
Alternatively, this reaction may involve a metallacycle such as C as an
intermediate.
3 (a) S. Saito, Y. Chounan, T. Nogami, T. Fukushi, N. Tsuboya,
Y. Yamada, H. Kitahara and Y. Yamamoto, J. Org. Chem., 2000, 65,
5350; (b) V. Gevorgyan, N. Tsuboya and Y. Yamamoto, J. Org. Chem.,
2001, 66, 2743; (c) S. Saito, M. M. Salter, V. Gevorgyan, N. Tsuboya,
K. Tando and Y. Yamamoto, J. Am. Chem. Soc., 1996, 118, 3970, and
references therein; (d) V. Gevorgyan, A. Takeda, M. Homma,
.
10 Compounds 3i and 3m showed anticancer activity with an average GI50
of 14.6 and 7.1 mM, respectively, on a tested panel of cancer cell lines
[e.g. HT29 (colon), H460 (lung), LoVo (colon)] (see ESI{).
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