5-Aroyl-2-pyrazolines

Aroyl-2-pyrazolines 217a,b arise in good yield in the reaction of a,/3-unsaturated ketones 216 with the heterocyclic hydrazonoyl halides 27 and 28, respectively (87JHC1665 88H695, 88MI3 90MI1). 

Z 75A- . 8mall amounts of the cyclic pyrazoline tautomer were detected only for derivatives containing strongly electron-withdrawing substituents X. Electron-withdrawing substituents Y on the A-aroyl group shift the equilibria 75A - 75A -Z 75A- [( 03)280] slightly in favor of the... 

Particularly in [32] it was shown that cycloaddition of the chalcones 10 and diazomethane is a regioselective process providing 3-aroyl-4-aryl-2-pyrazolines 12, most likely via heterocycles 11. These are the sole products irrespective of the bulkiness and/or the electronic influence of the two aryl moieties of the starting a,(3-unsaturated ketones 10 (Scheme 2.4). 

The synthesis and relative stability of 3,5-diacyl-4,5-dihydro-l//-pyrazoles prepared by dipolar cycloaddition of enones and a-diazoketones has been published <2004JOC9085>. 3-Acyl-4-aryl-2-pyrazolines have been synthesized by the reaction of a,/3-unsaturated ketones with diazomethane <1996IJB1091>. Ethyl diazoacetate added to 1,3-diarylpropenones in a regioselective fashion to give the intermediate 4,5-dihydto-3//-pyrazole derivative 1,3-hydride shift in the latter led to the formation of the isomeric ethyl 4-aryl-5-aroyl-4,5-dihydro-l//-pyrazole-3-carboxylate and ethyl 4-aryl-3-aroyl-4,5-dihydro-l/7-pyrazole-5-carboxylate in a ratio of 5 1 <2001RJ01517>. 1,3-Dipolar cycloaddition of 2-diazopropane with diarylideneacetones afforded diastereomeric bis-A -pyrazolines <1999T449>. 

The 1,3-dipolar cycloaddition of araldehyde hydrazones and araldoximes with 1-aroyl-2-arylsulfonylethenes in the presence of chloramine-T produces a mixture of 2-pyrazolines and 2-isoxazolines7 The thermally induced intramolecular 1,3-dipolar cycloaddition of 3-(alk-3-enylamino)-2,2-dimethylpropionaldehyde oximes (61) yields isoxazolo[4.3-c]pyridine derivatives (62) under mild conditions (Scheme 22)7 (/f)-Methylaluminium jS-binaphthoxide catalyses the formal 3 -I- 2-cycloaddition of 5-methoxy-2-(o-methoxyphenyl)oxazole with benzaldehyde or para- and meta-substituted benzaldehyde to produce cw-2-oxazoline-4-carboxylates with high enan-tioselectivity (90% ee)P... 

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