N-H insertion reactions of rhodium carbenoids: A modified Bischler indole synthesis

Synlett

Volumn , Issue 2, 1998, Pages 135-136

  Moody, Christopher J ^a   Swann, Elizabeth ^a  

^a UNIVERSITY OF EXETER   (United Kingdom)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0002890787     PISSN: 09365214     EISSN: None     Source Type: Journal    
DOI: 10.1055/s-1998-1610     Document Type: Article

References (13)

1. Bischler, A.: Brion, H. Chem. Ber. 1892, 25, 2860;
2. Bischler, A.; Firemann, P. Chem. Ber. 1893, 26, 1336.
3. Sundberg, R. J. The Chemistry of Indoles. Academic Press, New York, 1970;
4. Sundberg, R. J. Indoles, Academic Press, London, 1996.
5. Gribble, G. W. Contemp. Org. Synth. 1994, 1, 145.
6. For previous work on carbenoid N-H insertion reactions, see Aller, E.; Buck, R. T.; Drysdale, M. J.; Ferris, L.; Haigh, D.; Moody, C. J.; Pearson, N. D.; Sanghera, J. B. J. Chem. Soc., Perkin Trans. 1 1996, 2879, and references therein.
7. 2, have been reacted with anilines at 180-200°C to give 2-arylindoles, presumably by cyclisation (with rearrangement) of α-anilino arylketones: Blades, C. E.; Wilds, A. L. J. Org. Chem. 1956, 21, 1013. For a discussion of such rearrangements in the Bischler indole synthesis, see reference 2.
8. General method: A mixture of the substituted aniline 1 (2 mmol), diazocarbonyl compound 2 (2.6 mmol) and rhodium(II) acetate (0.04 mmol) in toluene or chloroform (25 ml) was heated under reflux for 1 h. The solvent was removed in vacuo and the residue purified by column chromatography.
9. 3a, mp 52-53°C; 3b, oil; 3c, mp 60-62°C; 3d mp 39-40°C; 3e, mp 109-111°C; 3f, mp 138-140°C; 3g, mp 85-86°C; 3h, mp 74-75°C; 3i, oil; 3j, oil.
10. For the use of Amberlyst®15 in related cyclisations to give benzofurans, see: Knölker, H.-J.; Fröhner, W. Tetrahedron Lett. 1996, 37, 9183.
11. General Method: To a stirring solution of the ketone 3 (1.5 mmol) in toluene (25 ml) was added Amberlyst® 15 (0.3 g). The solution was heated under reflux overnight. The resin was filtered off, the filtrate concentrated in vacuo and the residue purified by column chromatography.
12. 11 76-77°C); 4b, mp 47-48°C; 4c, mp 61-63 °C; 4d, 4-methoxy isomer, mp 90-92°C, 6-methoxy isomer, mp 93-94°C; 4e, mp 63-66°C; 4f, mp 178-180°C; 4g, mp 81-82°C; 4h, mp 55-56°C; 4i, oil; 4j, mp 102-104°C.
13. Bailey, A. S.; Birch, C. M.; Illingworth, D.; Willmott, J. C. J. Chem. Soc., Perkin Trans. 1 1978, 1471.