New tri- and tetra-substituted pyrroles via quinazolinium N1-ylides
Mino R. Caira,a* Emilian Georgescu,b Loredana Barbu,c Florentina Georgescu,b and Florea Dumitrascuc
aDepartment of Chemistry, University of Cape Town, Rondebosch 7701, South Africa
bOltchim Research Center, St. Uzinei 1, 240050 Ramnicu Valcea, Romania
cCenter for Organic Chemistry C.D. Nenitescu, Romanian Academy 202 B, Spl. Independentei, 060023 Bucharest, Romania
E-mail:
[email protected]
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Abstract
New tri- and tetra-substituted N-arylpyrroles were synthesized by one-pot reaction of 3,7- disubstituted quinazolinonium bromides with substituted alkynes having at least one electron- withdrawing substituent in 1,2-epoxybutane acting both as solvent and hydrogen bromide scavenger. Structural characterization of the new compounds was based on IR and NMR spectroscopy as well as on single crystal X-ray analysis.
Keywords: N-Arylpyrrole, 3,7-disubstituted quinazolinium N1-bromides, 1,3-dipolar cycloaddition reaction
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Introduction
Tri- and tetra-substituted pyrroles are known to possess a broad range of biological activity that includes antimycobacterial action, inhibition of both neuronal and inducible nitric oxide synthases (nNOS and iNOS respectively), antifungal activity, and inhibition of oxidosqualene cyclase (OSC).1 For this reason, efforts are constantly being directed towards finding new synthetic pathways or improving known synthetic strategies.2
Our interest in obtaining new N-bridgehead heterocycles by the 1,3-dipolar cycloaddition reaction of the heteroaromatic N-ylides3 led us to investigate the reaction between quinazolinonium N1-ylides and acetylenic dipolarophiles with the aim of obtaining pyrrolo[1,2- a]quinazoline derivatives. Surprisingly, instead of the expected pyrrolo[1,2-a]quinazolines, highly substituted pyrroles were obtained in moderate to good yields.4 The new tri- and tetra- substituted pyrroles were obtained starting only from unsubstituted 4(3H)-quinazolinone and thus the possibility of extending the reaction to substituted 4(3H)-quinazolinones was considered.
