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Synfacts 2010(2): 0149-0149  
DOI: 10.1055/s-0029-1219113
Synthesis of Heterocycles
© Georg Thieme Verlag Stuttgart ˙ New York

[2+3] Cycloaddition Approach to Multisubstituted N-Arylpyrroles

Contributor(s): Victor Snieckus, Johnathan Board
F. Dumitrascu, E. Georgescu, M. R. Caira*, F. Georgescu, M. Popa, B. Draghici, D. G. Dumitrescu
Romanian Academy, Bucharest, Oltchim Research Center, Ramnicu Valcea, Romania and University of Cape Town, Rondebosch, South Africa
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Publication History

Publication Date:
21 January 2010 (online)

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Significance

Reported is the synthesis of tetra- and trisubstituted pyrroles by the [2+3] cycloaddition of quinazolinium N1-salts and electron-poor alkynes followed by an interesting fragmentation reaction. The quinazolinium N1-salts were prepared by reaction of 3-methyl-4(3H)-quinazolin­one with 2-bromoacetophenones. Butyl oxirane is used as solvent and hydrogen bromide scavenger. The proposed mechanism is shown above and is supported by the isolation of intermediate A (R¹, R² = CO2Me) when dimethyl acetylenedicarboxylate (DMAD) is used as dipolarophile. The original targets of this reaction were the pyrrolo-[1,2-a]quinazolines B, whose synthesis by this methodology was precedented in different systems.