The Synthesis Of Pyrazoles Or Pyrazolines Via The Reaction Of1,3-Disubstituted Benzotriazolium Ylide With Electron-Deficient Alkynes Or Alkenes

Considering the strong nucleophilic activity and ring-opening possibility of1,3-disubstituted benzotriazolium ylide, the reactions between1,3-disubstituted benzotriazolium ylides and electron deficient alkynes or alkenes were applied to the synthesis of multisubstituted pyrazole or pyrazoline derivatives.Firstly, the reactions of1,3-disubstituted benzotriazolium ylides with a, β-unsaturated amides were conducted. The results showed that the reactions were highly depended on the structure of α, β-unsaturated amides. If the α, β-unsaturated amide with one or two hydrogen atoms bonded to the nitrogen atom was used, both1,5-diaryl-4,5-dihydro-1H-pyrazole-3-carboxamide and1,5-diaryl-4,5-dihydro-1H-pyrazole were formed.Secondly, a series of novel1,3,5-triaryl-2-pyrazolines were prepared via the reactions of1,3-disubstituted benzotriazolium ylides with phenylethylenes in good yields, and it was easy to be oxidated to form the corresponding1,3,5-triaryl-2-pyrazoles by DDQ, which provided a new access to the formation of1,3,5-triaryl-2-pyrazoles.Thirdly, it was found that the synthesis of1,3,5-triaryl-2-pyrazoles became more direct and convenient by the reactions of1,3-disubstituted benzylbenzotriazolium ylides with phenylacetylenes. The possible mechanism was also discussed.At last, the effect of carbonyl group on the alkynes was investigated via the reactions between1,3-disubstitued benzylbenzotriazolium ylides and1-phenylprop-2-yn-ones or1,3-diphenylprop-2-yn-ones derivatives. It was showed that the introducing of carbonyl group could improve the activity of alkynes and increase the yields of multisubstituted pyrazoles, which provided an economic and convenient synthesis of multisubstituted pyrazoles.