Abstract
5-Chloropyrazole-4-carbaldehydes were efficiently prepared via Vilsmeier reaction of 1H-pyrazol-5(4H)-ones with bis(trichloromethyl) carbonate-DMF instead of the traditional POCl3–DMF system. The Baylis–Hillman reaction of these aldehydes with activated alkenes promoted by various catalysts were investigated. It was found DMAP accelerated the reaction of methyl acrylate or acrylonitrile with the aldehydes, while in the case of but-3-en-2-one, a catalyst mixture of imidazole and L-proline (1:1) was efficient. Overall, the reactivities of the aldehydes were low.
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