Synthesis of indolizines and azaindolizines has received increasing interest during the last
years driven by a wide range of potential applications, from electroluminescent materials to
macrocyclic fluorescent sensors [1,2]. In particular, the interest in pyrroloimidazole derivatives
(PID) arises from their highly efficient blue fluorescence emission [3], which makes them
attractive materials in optoelectronics for blue organic light-emitting diodes.
The strategies adopted for construction of fluorescent PID I, are depicted in Scheme 1. To
obtain ylides derived from benzo[d]imidazol 1, we used the Kröhnke [4] salt method. Thus,
benzo[d]imidazolium salts 3 were prepared by treating 3-(1H-benzo[d]imidazol-1-
yl)propanenitrile 1 with methylbromoacetate 2a or ethylbromoacetate 2b. Then, for the obtaining
of highly fluorescent pyrroloimidazole derivatives 5 and 6, it was used a (3+2) dipolar
cycloaddition of benzo[d]imidazolium ylides 4, generated in situ from the corresponding
cycloimmonium salts, to methyl propiolate or DMAD.

The structure of the new compounds was proven by elemental (C, H, N) and spectral
analysis (IR, 1H NMR, 13C NMR, 2D-COSY, HMQC, HMBC). All the elemental and spectral
data are in accordance with the proposed structure.
Acknowledgements: To CNCS - UEFISCDI, grant PN-II-TE/ 0010 -79/05.10.2011 (director
assisting profesor Costel Moldoveanu) for financial support.
References:
1. B. Valeur, Molecular Fluorescence, Ed. Wiley-VCH, Weinheim, 2002.
2. M.A. Thompson and S.R. Forrest, Nature 2000, 403, 750.
3. T. Mitsumori, M. Bendikov, J. Sedo and F. Wudl, Chem. Mater. 2003, 15, 3759.
4. E. Krohnke, Ber. Dtsch. Chem. Ges. 1935, 68, 1177.