Aim and Objective: Pyrazolone sulfones have been reported to exhibit herbicidal and antibacterial
activities. In spite of their good bioactivities, only a few methods have been developed to prepare pyrazolone
sulfones. However, the substrate scope of these methods is limited. Moreover, the direct sulfonylation of pyrazolone
by aryl sulfonyl chloride failed to give pyrazolone sulfones. Thus, developing a more efficient method
to synthesize pyrazolone sulfones is very important.
Materials and Method:
Pyrazolone, aryl sulphonyl hydrazide, iodine, p-toluenesulphonic acid and water were
mixed in a sealed tube, which was heated to 100°C for 12 hours. The mixture was cooled to 0°C and m-CPBA
was added in batches. The mixture was allowed to stir for 30 min at room temperature. The crude product was
purified by silica gel column chromatography to afford sulfuryl pyrazolone.
Results:
In all cases, the sulfenylation products were formed smoothly under the optimized reaction conditions,
and were then oxidized to the corresponding sulfones in good yields by 3-chloroperoxybenzoic acid (m-CPBA)
in water. Single crystal X-ray analysis of pyrazolone sulfone 4aa showed that the major tautomer of pyrazolone
sulfones was the amide form instead of the enol form observed for pyrazolone thioethers. Moreover, the C=N
double bond isomerized to form an α,β-unsaturated C=C double bond.
Conclusion:
An efficient method to synthesize pyrazolone thioethers by iodine-catalyzed sulfenylation of
pyrazolones with aryl sulfonyl hydrazides in water was developed. Moreover, this method was employed to
synthesize pyrazolone sulfones in one-pot by subsequent sulfenylation and oxidation reactions.