Synthesis and Properties of Indolyl-dipyrroles Hillary K. Tanui, Erhong Hao and M. Graça H. Vicente Department of Chemistry, Louisiana State University Baton Rouge, LA 70803
[email protected] Introduction Dipyrrole-ethynes are important fragments in the synthesis of a variety of molecules, including indolyl-dipyrroles, porphycene and corrphycenes. The conventional method for the synthesis of these molecules involves three steps and uses a Sonogashira coupling reaction twice1,2 followed by functionalization of the ethyne group3. Herein we report a novel and shorter synthetic route for the preparation of these molecules involving a one-step double Sonogashira reaction4, as shown in the Scheme below. We also report the spectroscopic and ion-binding properties of these molecules.
(3a)
(2a)
Figure 1. Crystallographic structures of compounds 2a and 3a
Figure 5. Job’s plot for compound 3a forming complex showing a 2:1 stoichiometry, Δδ=δ(free)-δ(complex), r[3a] = mole fraction, [3a]= moles
Method Conclusions Figure 2. Crystallographic structure of molecule 3a complexed with fluoride ion
a
Scheme 1: Synthetic route for compounds 2 and 3. Reagents: a) Pd(0), CuI, CH3CN, DBU, H2O, CH≡CSMe3, room temperature for 2 days, 54%; (b) Pd(OAC)2, Iodoaniline, DMF, LiCl, K2CO3, 80˚ C, 3 days, 55%;
b
c
Figure 3. Fluorescence spectra titration for compound 3a with increasing amount of anions as TBA salts: a (F-, 0-100eq), b (Br-, 0-800eq), c (HSO4-, 0-1000eq).
Results Table 1. Photophysical properties and fluorescence quantum yield calculations5 for 2a and 3a in CH2Cl2 at room temperature. compounds
a
λmax (nm)
λema (nm)
Φb
Stokes shift (nm)
2a
339
414
0.01
75
3a
292
439
0.88
147
excitation at 290 nm, b fluorescence quantum yield was calculated using quinine sulfate as the standard (0.56 in 0.1 M H 2SO4 aqueous solution).
Figure 4. Changes in fluorescence observed upon addition of anions (10 equiv) as TBA salts to otherwise identical solutions of dipyrrole 3a (1.0 × 10-4 M in DMSO). From left to right: H2PO4- (A), HSO4- (B), I(C), Br- (D), Cl- (E), F- (F).
Indolyl-dipyrroles 3 were synthesized in two steps. These compounds showed interesting photophysical properties and high affinity for binding fluoride, as shown from fluorescence binding titration experiments using F-, Br- and HSO4- (as tetrabutylammonium salts). Crystals of the intermediate product 2a as well as compound 3a were grown and their molecular structures were confirmed by X-ray crystallography. The structure of the complex formed between compound 3a and Fions was also determined by X-ray crystallography. The Job’s plot was obtained and it showed that the complex has a 2:1 stoichiometry (3a:F-), in agreement with the X-ray crystallographic analysis.
REFERENCES 1. Cho, D. H.; Lee, J. H.; Kim, B. H. J. Org. Chem. 1999, 64, 8048-8050. 2. Tu, B.; Ghosh, B.; Lightner, D. A. J. Org. Chem. 2003, 68, 8950-8963. 3. Larock, R. C.; Yum, E. K.; Refvik, M. D. J. Org. Chem. 1998, 63, 7652-7662. 4. Mio, M. J.; Kopel, L. C.; Braun, J. B.; Gadzikwa, T. L.; Hull, K. L.; Brisbois, R. G.; Markworth, C. J.; Grieco, P. A. Org. Lett. 2002, 4, 3199-3202. 5. Fery-Forgues, S.; Lavabre, D. J. Chem. Education 1999, 76 1260-1264. 6. Job, P. Ann. Chim. App., 1928, 9, 113-203
Acknowledgments This work was funded by the US National Science Foundation. We thank Dr. Frank Fronczek for solving the X-ray structures.
