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Indoles - Sundberg R.J.

Sundberg R.J. Indoles - Academic press, 1996. - 95 p.
ISBN 0-12-676945-1
Download (direct link): indoles1996.djvu
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B. 6-Benzoyloxindole
A mixture of the above intermediate (23.1 g, 60 mmol) and tin powder (22.4 g, 190 mmol) in ethanol (150 ml) containing conc. HC1 (65 ml) was heated at reflux for 2 h. The solution was filtered hot and on cooling the product crystallized. It was recrystallized from nitromethane to give 11.4 g (80% yield) of the oxindole.
20
2 CATEGORY la CYCLIZATIONS
References
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2. S. P. Modi, R. C. Oglesby and S, Archer, Org. Synth. 72, 125 (1994).
3. C. J. Moody and K. F. Rahimtoola, J. Chem. Soc., Perkin Trans. 1 673 (1990).
4. P. Rosenmund and W. W. Flaase, Chem. Ber. 99, 2504 (1966); P. Rosenmund, D. Sauer and W. Trommer, Chem. Ber. 103, 496 (1970).
5. W. E. Noland and F. J. Baude, Org. Synth., Coll. Vol К567 (1973).
6. E. E. Garcia and R. I. Fryer, J. Heterocycl. Chem. 11, 219 (1974).
7. M. Arcari, R. Aveta, A. Brandt, L. Cecchetelli, G. B. Corsi and M. Di Rella, Gazz. Chim. Ital. 121, 499 (1991).
8. M. Prashad, L. La Vecchia, К Prasad and O. Repic, Synth, Commun. 25, 95 (1995).
9. S. Raucher and G. A. Koolpe, J. Org. Chem. 48, 2066 (1983).
10. Y. Tsuji, S. Kotachi, K..-T. Huh and Y. Watanabe, J. Org. Chem. 55, 580 (1990).
11. R. R. Webb, II, М. C. Venuti and C. Eigenbrot, J. Org. Chem. 56, 4706 (1991).
12. H. Plieninger, E. Meyer, F. Sharif-Nassirian and E. Weidmann, Liebigs, Ann. Chem. 1475 (1976).
13. S. J. Danishefsky and G. B. Phillips, Tetrahedron Lett. 25, 3159 (1984).
14 H. Maehr and J. Smallhcer, J. Am. Chem. Soc. 107, 2943 (1985).
15. A. Kasahara, T. Izumi, S. Murakami, K. Miyamota and T. Hino, J. Heterocycl. Chem. 26, 1405 (1989).
16. T. Izumi, M. Soutome and T. Miura. J. Heterocycl. Chem. 29, 1625 (1992).
17. J. Bourdais and C. Germain, Tetrahedron Lett. 195 (1970).
18. M. Makosza, W. Danikiewicz and K. Wojciechowski, Liebigs Ann. Chem. 203 (1988).
19. J. E. Macor and J. M. Wehner. Tetrahedron Lett. 32, 7195 (1991).
20. J. P. Marino and C. R. Hurt, Synth. Commun. 24, 839 (1994).
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2.4 INDOLES FROM o-AMINO- OR o-NITROPHENYLACETYLENES
o-Aminophenylacctylenes or N-protected derivatives can be cyclized to indoles by an endo-dig addition. The most useful methods employ Pd(II) catalysts. Indol-3-ylpalladium intermediates are involved in the cyclization and this opens the possibility for tandem cyclization-substitution procedures which can introduce a 3-substituent. The ultimate starting materials arc usually o-haloanilines which are coupled with acetylenes.
2.4 INDOLES FROM o-AMINO- OR o-NITROPHENYLACETYLENES
21
i
H
Rudisill and Stille developed a two-step procedure in which 2-bromo-or 2-trifluoromethanesulfonyloxyacetanilides were coupled with tri-n-butyl-stannylacetylenes in the presence of Pd(PPh3)4[l], Cyclization was then effected with PdCl2(CH3CN)2. The conditions are compatible with a variety of carbocyclic substituents so the procedure can provide 2-substituted indoles with carbocyclic substituents. The reported yield ranges from 40% to 97% for the coupling and from 40% to 82% for cyclization.
PdCI2(MeCN)2 —- R (2-i2> i
H
2-fodo-iV-(methanesulfony])aniHnes can be converted to 2-substituted indoles by reaction with terminal acetylenes in a one-pot process involving Cul, Et3N and Pd(PPh3)2Cl2 as the catalyst system[2]. Yields ranged from 40% to 70%) for alkyl, aryl and several oxygenated alkyl substituents.
These Pd-catalysed procedures appear to be preferable to earlier ones in which Cu(I)[3] or Hg(II)[4] were used to induce cyclization. Some additional examples are given in Table 2.3.
Starting with 2-ethynylaniline, Cacchi and co-workers have prepared 2-aryl and 2-(cycloalkenyl)indoles by coupling followed by cyelization[7]. The reagents for the coupling step are Pd(PPh3)4:CuI:Et2NH. The cyclization is
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