[E013]
Micha³ Pajda, Dariusz Bogdal*
Department of Polymer Chemistry
and Technology,
Krakow University of Technology,
ul. Warszawska 24,
31-155 Krakow, Poland
* e-mail: pcbogdal@cyf-kr.edu.pl
Abstract
Microwave irradiated Vilsmeier-Haack
reactions with carbazole derivatives and hydroxyaromatic derivatives was
presented. As a result the appropriate aromatic aldehydes with a high yield were
obtained.
Keywords
microwaves, Vilsmeier-Haack reaction,
aromatic aldehydes
Introduction
Vilsmeier-Haack reagents are widely
used for an introduction of formyl group into various activated aromatic and
heteroaromatic compounds [1].
When using this method, reaction lasts from few hours to 2 days [2].
Therefore we decided to find more suitable method of synthesis. Our main
assumption was that microwave irradiation is used in many different kind of
synthesis with a good results. Moreover, in most of the cases usage of microwave
irradiation allows to reduce time of reaction in comparison to conventional
heating [3].
Obtained compounds can be used as half-products in organic synthesis.
Experimental
All irradiation experiments were
carried out in a multimode microwave rector PLAZMATRONIKA (Poland). IR spectra
were recorded on FT-IR Biorad FTS-165 spectrophotometer. GCMS spectra were
determined on GCMS 5890 Series II Hewlett-Packard gas chromatograph equipped
with (25m x 0.25mm x 0.25mm) column with Hewlett-Packard 5971 Series Mass
Selective Detector.
All starting materials and solvents were purchased from
Aldrich Chemicals Co. and were used without any purification.
General
method of formylation,
7ml (75mmol) of POCl3 was added slowly to 20ml
DMF. The yellow solution was allowed to stir at room temperature for one hour.
37.5mmol of appropriate compound was added over 30min. The mixture was stirred
for 1 hour under microwave irradiation. Then the mixture was poured into
vigorously stirred water and product was extracted twice with 1:1
cyclohexane/EtOAc mixture. The solution was evaporated and recrystalised from
ethanol. The final product was analysed by GCMS and IR.
Results and Discusion
In summary, formylation of carbazole and hydroxyaromatic derivatives proceed faster under microwave condition. A halomethylenium salt formed from POCl3 and DMF has a dual role of reagent as well as solvent, therefore we don't need additional solvents.
References
[1] Vilsmeier, A.; Haack,
A.: Ber. 1927,60,119
[2] US Pat 4794184; Zhang Y., Wada T.,
Sasabe H.; J. Chem. Soc., Chem. Commun; 1996, 5; 621-622, US Pat 5736284;
Maruyama S., Zhang Y., Wada T., Sasabe H, J. Chem. Soc., Perkin Trans. 1, 1999,
1,41-46;
[3] P. Lidstrom, J. Tierney, B. Wathey, J. Westamn;
Tetrahedron; 2001, 57, 9225; L. Perreux, A. Loupy; Tetrahedron; 2001, 57, 9199;
A. K. Bose, M. S. Manhas, S. N. Ganguly, A. H. Sharma, B. K. Banik; Synthesis;
2002, 1578-1591; A. Loupy (Ed.); Microwave in Organic Synthesis, Wiley-WCH,
Weinheim, 2002