A high yield and pilot-scale process for the preparation of adapalene

Strategies that were adopted during the process development of adapalene to achieve a cost-effective commercial-scale synthesis are described herein. These included (1) the use of AcOH/H2SO4 to afford 2-(1-adamantyl)-4-bromophenol in quantitative yield; (2) the dimethyl sulfate methylation to enhance the yield of methylation to 95%; (3) direct conversion of the Grignard reagent into methyl 6-(3-(1-adamantyl)-4-methoxyphenyl)-2-naphthoate by the catalysis of both PdCl2(PPh3)(2) and ZnCl2 in high yield; (4) the use of EDTA-disodium salt dihydrate to ensure the heavy metal's content within acceptable limits; (5) the use of toluene to simplify the original chromatographic purification to recrystallization. The pilotscale synthesis of adapalene is described in detail in the Experimental Section.