Studies on Heteroaromaticity. LII. Syntheses and Reactions of α-Acetylenic Ketones Containing Nitrofuran Ring

Abstract 2-(5-Nitro-2-furyl)-1-phenyl- (IVa), -p-methylphenyl- (IVb) and -(2-furyl)-acetylene (IVc) were prepared by condensation of nitrofurfural with the corresponding aryl methyl ketones, followed by bromination and dehydrobromination. Addition of aniline and cyclohexylamine to IVa afforded simple adducts Va and VIa respectively. Treatment of IVa,b with hydroxylamine, hydrazine hydrate, semicarbazide and benzamidine gave isoxazoles (VIIIa,b), pyrazoles (VIIIa,b), 1-carbamidopyrazoles (IXa,b) and pyrimidines (Xa,b) respectively. When treated with benzonitrile oxide at room temperature, IVa afforded isoxazole XIa together with furoxan, but the thermal 1,3-dipolar reactions of IVa,b with 5-nitro-2-furocarbonitrile oxide afforded exclusively isoxazoles XIIa,b. For comparison, 5-nitro-2-furfurylidenebenzophenone (IIa) was treated with benzonitrile oxide at room temperature to afford an isomeric mixture of the isoxazolines XIIIa and XIVa together with furoxan. Similar treatment of 5-nitro-2-furfurylideneacetone afforded similar results affording a mixture of XV and XVI together with furoxan. When treated with phenacylpyridinium ylide, IVa,b afforded pyrrocolines XVIIa,b. The structural elucidation of the products was carried out on the basis of the spectral data.