| Popis: |
β-Acylvinylphosphonium salts (1) react with diazomethan to form 4-acylpyrazoles (3). The formation can be explained by a primary reaction of the nucleophilic C-atom of the diazo compound with the β-C-atom, to the phosphorus (i.e. the α-C-atom relative to the CO group). The well known reaction of diazo compounds with β-chlorvinylketones takes place in the reverse manner forming only 3-acylpyrazoles. Therefore, using β-acylvinylphosphonium salts, the cycloaddition can be directed to yield 4-acylpyrazoles. The addition of diazoketones to β-acylvinylphosphonium salts sometimes also affords 3,5-diacylpyrazoles (4). |
