Synthesis Of3-n-propyl-2,4-dihydroxy Acetophenone

3-n-Propyl-2,4-dihydroxyacetophenone acts as a common and vital intermediate for the preparation of a series of pharmaceuticals, like leukotriene receptor antagonists, metabotropic glutamate receptor potentiators, and peroxisome proliferator-actived receptor ligands, which are used for the treatment of asthma, neurological problem and atherosclerosis, respectively.In this paper, the synthetic technology of3-n-propyl-2,4-dihydroxyacetophenone was improved and optimized on the basis of reported literatures, and the title compound was obtained using m-dihydroxybenzene as the starting material via acylation, allylation, Claisen rearrangement and hydrogenation reduction. Compared with the reported literatures, the improvements and innovations of this paper were as follows:First of all, the present approach was cost efficient. In the process of synthesizing4-allyloxy-2-hydroxyacetophenone, by using NaBr as catalyst, allyl bromide which is the traditional expensive etherification agent was replaced with the much cheaper allyl chloride. On the other hand, for the Claisen rearrangement diphenyl ether which was performed as solvent and recycled, could not only improve the yield but also make the synthetic route more eco-friendly.The effect of reaction parameters, including temperature, solvents, molar ratio of materials in each step on yields were investigated in detail, and the optimal reaction conditions were obtained. The acylation reaction which used acetic acid as acylation agent and ZnCl2as catalyst was carried out under reflux for5h in81.2%yield. The allylation reaction using allyl chloride as allylation reagent and NaBr as catalyst was carried out at70℃for14h, and98.6%yield was obtained. In Claisen rearrangement which was carried out at205℃for4.5h, diphenyl ether was used as solvent and the yield increased to67.4%. In the final step, the hydrogenated reduction with Pb/C (5%) as catalyst was carried out at45℃for6h in87.3%yield.The overall yield was no less than47.8%higher than that reported in the literature (37.0%). The process is much of industrial value because of high yield, cheap and available materials and convenient operations. The structure of the main compounds were confirmed by1H-NMR、GC-MS and IR.