We describe herein an efficient protocol for the one-pot synthesis of 4-organylselanylpyrazoles by direct cyclocondensation and C-H bond selenylation reactions starting from hydrazines, 1,3-diketones and diorganyl diselenides promoted by Oxone®. The products were obtained through a metal catalyst free methodology, under mild conditions, in short reaction times and moderate to excellent yields.
Keywords:
Oxone®; organoselenium compounds; pyrazoles
| entry | 3a / mmol | Oxone® / mmol | Temperature / ºC | time / h | Solvent | Yieldb b yields are given for isolated products; 4a / % |
|---|---|---|---|---|---|---|
| 1 | 0.125 | 0.500 | 50 | 24.0 | CH3CN | 50 |
| 2 | 0.188 | 0.500 | 50 | 24.0 | CH3CN | 85 |
| 3c c the excess of 3a was recovered by column chromatography. | 0.250 | 0.500 | 50 | 1.0 | CH3CN | 97 |
| 4 | 0.250 | 0.250 | 50 | 1.0 | CH3CN | 54 |
| 5 | 0.250 | 0.500 | 25 | 2.0 | CH3CN | 68 |
| 6 | 0.250 | 0.500 | reflux | 0.5 | CH3CN | 85 |
| 7c c the excess of 3a was recovered by column chromatography. | 0.250 | 0.500 | 50 | 0.5 | CH3COOH | 98 |
| 8 | 0.250 | 0.500 | 50 | 1.0 | EtOH | 83 |
| 9 | 0.250 | 0.500 | 50 | 24.0 | H2O | 40 |
| 10 | 0.250 | 0.500 | 50 | 2.0 | PEG-400 | 71 |
| entry | Hydrazine 1 | 1,3-Diketone 2 | Diselenide 3 | Product 4 | Yieldb b yields are given for isolated products; / % |
|---|---|---|---|---|---|
| 1 | 98 | ||||
| 2 | 90 | ||||
| 3 | 89c c the mixture of regioisomers 4c/4c' (96:4) was obtained and determined by GC-MS analysis; | ||||
| 4 | 69d d the reaction was carried for 1.0 h. | ||||
| 5 | 44d d the reaction was carried for 1.0 h. | ||||
| 6 | 75d d the reaction was carried for 1.0 h. | ||||
| 7 | 77 | ||||
| 8 | 84 | ||||
| 9 | 81 | ||||
| 10 | 90 | ||||
| 11 | 90 | ||||
| 12 | 58 | ||||
