The 2-(alkylcarbonyl)benzoic acids obtained by esterification of phthalic anhydride are converted into azide derivatives: alkyl 2-[(azidocarbonyl)amino]benzoates and to ureas: dialkyl 2,2′-[carbonylbis(azanediyl)]dibenzoates. These transformations were carried out using classical Curtius rearrangement conditions in the presence of diphenylphosphoryl azide (DPPA) in a basic medium, followed by hydrolysis. Subsequently, a final condensation reaction of these urea derivatives enabled us to obtain, for the first time, the new alkyl derivatives, alkyl 2-[2,4-dioxo-1,2-dihydroquinazolin-3(4H)-yl]benzoates. All the new compounds obtained in satisfactory yields were characterized by 1H and 13C NMR, and by X-ray crystallographic analysis.
Background:
In this current work, a new synthesis strategy was developed to obtain 1,3,4-trisubstituted pyrazoles derivatives.
Methods:
A series of 1,3,4-trisubstituted pyrazoles have been prepared via 1,3-dipolar cycloaddition reaction of 3-phenylsydnones with a variety of alkenes derivatives, symmetric and non-symmetric alkynes derivatives, N-phenyl-maleimide, N-benzyl-maleimides and maleic anhydride under conventional manner.
Results:
Moreover, in this work it has been demonstrated that the 4-bromopyrazole intermediates can be further functionalized by a combination of Suzuki-Miyaura cross coupling reactions with aryl-boronic acids and N-arylation reactions of anilines.
Conclusion:
In summary, we have developed a new method to obtain 1,3,4 triarylated pyrazoles through 3-phenylsydnone 1,3-dipolar cycloadditions. By comparing the different reactions, it is apparent that high temperatures and xylene as solvent are key to achieve pyrazoles derivatives and the best yields were observed for symmetric and non-symmetric alkynes as dipolarophiles.
The title compound, C10H12ClNO2, is close to planar (r.m.s. deviation for the 14 non-H atoms = 0.053 Å). In the crystal, inversion dimers linked by pairs of N—H⋯Oc (c = carboxyl) hydrogen bonds generate R
2
2(10) loops.
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