3 Diels-Alder reactions in 1 go
|A mixture of 4, 4-dimethyl-3-oxo-pentanenitrile (1, 34 mM), 2, 4-dinitrophenyl hydrazine hydrochloride (2, 35 mM) and 50 mL absolute ethanol along with few drops of AcOH were heated at the reflux temperature for overnight and cooled to room temperature. The mixture was evaporated under vacuum and the residue thus obtained was washed with ether, suspended in EtOAc, and treated with 1 M NaOH solution. The organic layer then separated, washed with brine, dried over anhydrous magnesium sulphate and concentrated. The solid which separated was collected, then washed with a mixture of ether and hexane to give 5-amino-3-t-butyl-1-(2', 4'-dinitro)phenyl-1H-pyrazole (3) .|
|To a solution of 5-amino-3-t-butyl-1-(2', 4'-dinitro)phenyl-1Hpyrazole (3, 9.3 mM) in dichloromethane (5 mL), triethyl amine (23 mM) was added drop wise. The appropriate benzoylchlorides (4a-k, 12 mM) in dichloromethane were added to the above reaction mixture drop wise and stirred for 3 hours at room temperature. The mixture was further diluted with dichloromethane and washed with water, brine followed by once again with water. Sodium sulfate was used to dry the organic layer; solvent was removed under vacuum to get the final derivatives (5a-l). All the compounds were purified over silica to get pure N-(3-tert-butyl-2, 4-dinitro-1-phenyl-1H-pyrazol-5-yl) benzamides (5a-l).|
|Yield: 85%, m.p.: 190-192°C,|
IR (KBr) ν cm: 3362 cm (NH str.), 3020 cm (CH str. aromatic), 2950 cm (CH str. methyl), 1643 cm (NH bnd)
H NMR (CDCl) δ (ppm): 1.23 (s, 9H, t-butyl), 6.18 (s, 1H, C, pyrazole), 7.15-7.55 (m, 3H, C', C', C' aromatic), 7.7-7.8 (m, 2H, C, C, aromatic), 7.9-8.1 (d, 2H, C', C', aromatic), 8.2 (s, 1H, C, aromatic), 9.61 (bs, 1H, NH amide).
ESI-MS (m/z): 410, 100% [M+H].