Unambiguous characterisation of dienylimines as intermediates in Fischer indolisation of o-substituted N-trifluoroacetyl enehydrazines

Abstract

Thermal cyclisation of o-substituted N-trifluoroacetyl enehydrazines was systematically investigated and found to proceed via dienylimine intermediates, which were unambiguously characterised by X-ray and spectral analysis.

References

1. Reviews of Fischer indole synthesis: B. Robinson, Chem. Rev., 1963, 63, 373; B. Robinson, Chem. Rev., 1969, 69, 227; B. Robinson, The Fischer Indole Synthesis, Wiley, New York, 1982; D. L. Hughes, Org. Prep. Proced. Int., 1993, 25, 609.
2. K. Bast, T. Durst, R. Huisgen, K. Lindner and R. Temme, Tetrahedron, 1998, 54, 3745.
3. G. S. Bajwa and R. K. Brown, Can. J. Chem., 1969, 47, 785.
4. Recently we found a novel synthetic route for indoles (or indolines)via thermal cyclisation of N-trifluoroacetyl enehydrazines. O. Miyata, Y. Kimura, K. Muroya, H. Hiramatsu and T. Naito, Tetrahedron Lett., 1999, 40, 3601.
5. C. S. Barnes, K. H. Pausacker and C. I. Schubert, J. Chem. Soc., 1949, 1381.
6. The crystal contains two independent molecules in the asymmetric unit. Both molecules have disordered CF₃ groups with occupancy factor of 0.67/0.33 and 0.81/0.19, respectively and one of the molecules has additional disorder at the fused cyclopentane (C₁₇-C₁₈) with occupancy factors of 0.56 and 0.44. Crystal data for cis-syn-6a: C₁₄H₁₅F₃N₂O₂, mp 140–141 °C, triclinic, P 1̄, a= 11.277(2), b= 12.015(2), c= 11.056(2)Å, α= 97.87 (1), β= 94.66(2), χ= 71.73(1)°, V= 1408.1(4)ų, Z= 4, µ= 1.056 mm^–1, D_c= 1.416 mg m^–3, F₀₀₀= 624, T= 293 K. Final R value was 0.0684 for 4788 reflections. CCDC 182/1467. See http://www.rsc.org/suppdata/cc/1999/2429/ for crystallographic data in .cif format.
7. H. Ishii, Acc. Chem. Res., 1981, 14, 275.
8. Y. Murakami, H. Yokoo, Y. Yokoyama and T. Watanabe, Chem. Pharm. Bull., 1999, 47, 791.
9. G. S. Bajwa and R. K. Brown, Can. J. Chem., 1970, 48, 2293.