Reactions of 2,4-diphenylbutadiene-1,4-sultone with some 1,2-and 1,3-nitrogen binucleophiles

Treatment of 2,4-diphenylbutadiene-1,4-sultone with hydrazine in boiling EtOH gives 1-amino-2,4-diphenyl-1 H -pyrrole. On treatment of 2,4-diphenylbutadiene-1,4-sultone with phenyl hydrazine in glacial acetic acid, 4,5-dihydro-5-methyl-1,3,5-triphenyl-1 H -pyrazole was isolated. On the other hand, 2,4-diphenylbutadiene-1,4-sultone reacts with 4 H -1,2,4-triazol-3-amine and 5-amino-3-phenyl-1 H-pyrazole to afford the novel heterocyclic compounds 2-(2,2-dioxo-4-phenyl-3,4-dihydro-8 H -2 λ 6 -[1,2,4]triazolo[5,1-c ][1,2,4]thiadiazin-4-yl)-1-phenylethan-1-one, the structure of which was established by X-ray crystallography, and 2-(2,2-dioxo-4,7-diphenyl-3,4-dihydro-6 H -pyrazolo[5,1-c ][1,


Introduction
Sultones are valuable compounds containing the -SO 2 -O-group as part of a ring, i.e. an internal ester of a hydroxy-sulfonic acid.These heterocycles can react with a variety of nucleophilic compounds to introduce an alkyl sulfonic acid group. 1 Whereas sultones are sulfur analogues of lactones, they often behave differently when reacting with nucleophiles.6][7] To the best of our knowledge, the reactivity of sultones, especially of 2,4-disubstituted butadiene-1,4-sultones, towards 1,2-and 1,3-binucleophiles has not yet been reported.In view of this, and in continuation of our current interest in the chemistry of 1,2-and 1,3-binucleophiles towards various types of dienophile, [8][9][10][11] the goal of the present study was the examination of the reactivity of 2,4-diphenylbutadiene-1,4-sultone towards selected 1,2-and 1,3binucleophiles.

Results and Discussion
The reaction of 2,4-diphenylbutadiene-1,4-sultone (strictly, 4,6-diphenyl-1,2-oxathiin 2,2dioxide) (1) with hydrazine hydrate was carried out in boiling EtOH.The progress of the reaction was monitored by TLC, which showed that conversion of the starting material was complete after 10 h.The structure of the product, separated using column chromatography (n-hexane/ethyl acetate-9/1), is proposed to be 1-amino-2,4-diphenyl-1H-pyrrole (2) (Scheme 1) on the basis of its spectroscopic data.The 1 H NMR spectrum of compound 2 revealed the presence of a signal at 5.45 ppm characteristic of an NH 2 group, and H-C(3) and H-C(5) of the pyrrole ring were observed as singlets at 6.55 and 7.46 ppm.Compound 2 has been reported previously, prepared from γ-bromodypnone. 12

Scheme 1
The formation of compound 2 is assumed to take place via nucleophilic attack by an amino group of the hydrazine at the carbon-oxygen bond in 1 to form the non-isolable intermediates 3a and 3b leading to 2 via loss of H 2 SO 3 (Scheme 2).Filimonov and his group 13 have reported previously the reaction of 2,4-dinitrophenylhydrazine with 2,4-diphenylbutadiene-1,4-sultone (1) in aqueous acetic acid to obtain acetophenone 2,4-dinitrophenylhydrazone, formed by the reaction of acetophenone [from decomposition of the sultone in the water-acid mixture] with 2,4-dinitrophenylhydrazine.
In the present study, the reaction of 1 with phenylhydrazine was carried out in boiling glacial acetic acid for 18 h, and 2,5-dihydro-5-methyl-1,3,5-triphenyl-1H-pyrazole (4) was isolated after chromatographic separation (Scheme 3).The structure of compound 4 was established on the basis of its spectroscopic data.The 1 H-NMR spectrum of compound 4 revealed the presence of two characteristic signals at 2.42 and 7.34 ppm corresponding to CH 3 and CH-pyrazole protons, and in addition a signal at 13.12 ppm corresponding to the NH group.
As presented in Scheme 4, the formation of compound 4 could occur via Michael addition of phenylhydrazine to the dienylsulfonate unit to give 5 followed by ring opening, loss of sulfur trioxide, proton transfer (arrows on 6) and a final ring closure (arrows on 7) to generate the dihydropyrazole system.][10][11] They were used as Michael donors in reactions with electrophilic substrates, where the reaction was initiated by the attack of the NH 2 group onto an electron-deficient center followed by cyclization via addition/elimination to give fused heterocycles. 10,11The behavior of 2,4-diphenylbutadiene-1,4-sultone (1) towards some 1,3-binucleophilic aminoazoles was investigated.Thus, treatment of 1 with 4H-1,2,4-triazol-3-amine (8)  The formation of compound 9 can be explained on the basis of an initial sulfonamide formation via addition of the exocyclic NH 2 in 4H-1,2,4-triazol-3-amine (8) on the sulfonate function in 1 followed by protonation of the dienolate and then intramolecular aza-Michael addition as outlined in Scheme 6 to afford compound 9.

Scheme 6
The structure of compound 9 was established on the basis of the spectroscopic data.The 1 H NMR spectrum revealed the presence of signals characteristics for two CH 2 groups (doublets at 3.82 and 4.22 ppm), CH-triazole (singlet at 7.56 ppm) and a D 2 O-exchangeable NH (8.13 ppm).The mass spectrum of compound 9 had a peak at m/z 368 corresponding to its molecular ion.Moreover, the structure of compound 9 was unambiguously solved by X-ray diffraction analysis as shown in Figure 1.The reaction of 2,4-diphenylbutadiene-1,4-sultone (1) with 5-amino-3-phenyl-1H-pyrazole (11), was carried out in boiling EtOH/DMF.The progress of the reaction was monitored by TLC, which showed that conversion of the starting materials was complete after 26 hours improved to 49% yield after 20 minutes using microwave heating (Scheme 7).
The structure of the product is proposed to be 2 (12) on the basis of the spectroscopic data.The IR spectrum of the later product revealed absorption bands at 3116 and 1662 cm -1 corresponding to NH and C=O groups, respectively.The 1   (1) with phenylhydrazine.To a solution of the sultone 1 (0.284 g, 1 mmol) in glacial acetic acid (10 mL) was added phenylhydrazine (0.18 g, 1.5 mmol).The reaction mixture was refluxed for 18 h then left to cool, and 10 mL of H2O was added.The resulting yellowish solid precipitate was collected by filtration, washed with EtOH, dried, and then purified using column chromatography (n-hexane/ethyl acetate-8/2-silica) to afford 2,5-dihydro-5-methyl-1,3,5-triphenyl-1H-pyrazole (4).