Reaction #48034

Reaction equation

ethyl 2-chloro[(4-chlorophenyl) hydrazono]acetate

styrene

triethylamine

→

ethyl 1-(4-chlorophenyl)-5-phenyl-4,5-dihydro-(1H)-pyrazole-3-carboxylate

Yield 94.0%

Solvents

benzene

Conditions

Workup

1. 1
   Temperaturethe resulting solution is heated
2. 2
   Temperatureat reflux temperature for 1 hour
3. 3
   Otherthe formed precipitate is removed by filtration
4. 4
   Washwashed with toluene
5. 5
   ConcentrationThe filtrate is concentrated in vacuo
6. 6
   Otherpurified by flash chromatography (silica gel, dichloromethane)

Procedure

Part B: To a stirred boiling solution of ethyl 2-chloro[(4-chlorophenyl) hydrazono]acetate (22.95 gram, 0.088 mol) and styrene (30.3 ml, 0.264 mol) in benzene (140 ml) is added triethylamine (34.3 ml, 0.247 mol) and the resulting solution is heated at reflux temperature for 1 hour. The resulting solution is cooled to room temperature and the formed precipitate is removed by filtration and washed with toluene. The filtrate is concentrated in vacuo and purified by flash chromatography (silica gel, dichloromethane) to give ethyl 1-(4-chlorophenyl)-5-phenyl-4,5-dihydro-(1H)-pyrazole-3-carboxylate (27.2 gram, 94% yield) as a syrup which slowly solidifies on standing. 1H-NMR (200 MHz, CDCl3): 1.38 (t, J=7 Hz, 3H), 3.06 (dd, J=18 and 7 Hz, 1H), 3.73 (dd, J=18 and 13 Hz, 1H), 4.33 (q, J=7 Hz, 2H), 5.38 (dd, J=13 and 7 Hz, 1H), 7.02 (br d, J=8 Hz, 2H), 7.08-7.40 (m, 7H).

Source