Synthesis and antimicrobial activity of furan-containing isoxazoles, triazoles, and 1,4-diketones

tion of 1,3-dipoiar cycloadditi0n products of 5-styryl-2-furoy lmethylenetriphenylphosphonium ylides and the antimicrobial activity of the synthesized compounds. It is already known that aroylmethylenetriphenylphosphonium ylides react with acid chlorides of ~-oxQhydroxamic acids to form the corresponding isoxazoles [6]. The authors of this work assumed that the formation of the isoxazole ring goes through the oxime phosphonium rearrangement. We used that method for the synthesis of furan-containing isoxazoles. Thus, the phosphonium ylides (Ia-c) were allowed to react with ~-chloro-~-isoni trosoacetophenone (II) [7] in the presence of Et3N in a modification of the method of [6] which was Et~N was introduced not to the reagent mixture, but to the solution of II. The precipitate thus occurring was identified as Et3N.HCI. This confirmed our proposal that Et2N does not "strip off" the ylideproton, and a significantly stronger acid, the oxime, thus forms PhCOC~N + O. When Et~N. HCI is removed from the reaction mixture, the possibility of its participation in the reactions subsequently taking place is excluded, and then the ylide solution Ia-c was added to the filtrate. We propose that in the given case the formation of the isoxazole is realized by a 1,3rdipolar cycloaddition of the N-oxide of benzoylnitrile generated in situ to the double bond of the enolbetaine structure of the phosphonium ylide. We confirmed the existence of the N-oxide of benzoylnitrile with the help of IR spectra of the reaction mixture, in which the valence oscillation bands of the C~N bond at 2260 cm -l disappeared with time. The structures of the isoxazoles IIIa-c were confirmed by IR spectral data, which con