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-The acetylation of 2-krovalerylthiophene has been studied. Condensation of P-acetylthiopene with ethyl acetate afforded 2-thenoylacetone, which reacted with acrylate ester (Michael condensation). Ureidomethylent+2-thenoylacetone was prepared and cyclized to the Qhenoylpyrimidine. Mass spectra of 2-monoacyl-, 2,54acyl-, and 2-benz.oylthiophenea were determined and their fragmentation patterns are discus&. a-Cleavage to the carbonyl group is the dominant feature affording the most prominent ion in most cases. The spechum of 2-benzoylthiophene suggests that loss of mass units 28 with the phenyl migration from the molecular ion is a likely occurrence.
Tm (M-28) ion associated with loss of carbon monoxide from the molecular ion has been reported for the mass spectra of benzophenone,' 2benzoylfuran,$ and Zbenzoylthiazole.8 It is the purpose of the present study to see if such a behaviour induced by electron bombardment also prevails for 2-acyl-and 2-aroylthiophenes.
Another object is to establish the fragmentation patterns of acylthiophencs, since the only reported mass spectrum of acylthiophene is that of 3-acetyl-4-hydr0xythiroxythiophene.q For this purpose several unknown 2-acyl-and 2-aroyhhiophenes were prepared, which are additionally recorded in this paper. 5'ynrtire.r. Although various reagents have been employed for the acylation of thiophene,&' acylation of 2-acylthiophem! has met little success. Condensation of 2-acetylthiophene (I) with isovaleric chloride or isovaleric acid using zinc chloride or phosphorus pentoxide failed whereas the reaction of 24sovalerylthiophene (II) with acetic acid in the presence of phosphorus pentoxide afforded diacylthiophene in poor yield. The NMR spectrum of this compound in deuterochloroform shows a singlet at 2.30 T alone in the aromatic region, which is compatible only with 2-acetyl-5isovalerylthiophene (III) and excludes the other possible alternative, 2,4-diacylthiophene.
Condensation of 2-acetylthiophene (I) with ethyl acetate in the presence of sodium afforded 24henoylacetone (IV), from which two compounds were obtained. An