Reports: B1
46094-B1 Efficient Synthesis of Heterocycles with the Aid of Electrophilic Cyclizations and Fluorous Chemistry
Ligand-free synthesis of pyrroles with the aid of acetylenic Schmidt reaction, starting from of 1,4- and 1,2,4-, mostly aryl-substituted, but-3-yn-1-yl (homopropargyl) azides, was investigated with the use of metal catalysts. A variety of zinc-containing compounds were screened. The best results were acquired with the use of a catalytic amount of zinc chloride etherate (usually 20 mol %) in dichloroethane at reflux. The reaction can be carried out in a significantly lower timeframe when it is accelerated through a microwave. 2,5-Di- and 2,3,5-trisubstituted pyrroles were obtained in high to moderate yields (91–41%); both conventional and microwave protocols furnished comparable results in this respect. The μ-oxo-tetranuclear zinc cluster Zn4(OCOCF3)6O gave comparable results, but was not pursued for preparative reactions since it was not commercially available.
DSC studies determined the stability of the azides used.
A crystal structure of 2-(4-fluorophenyl)-5-(4-methylphenyl)-1H-pyrrole was confirmed by X-ray crystallography. It shows coplanar structure of the pyrrole ring and its aryl substituents in crystalline form.
