Ablukast

Abstract: An efficient synthesis of the leukotriene antagonist ablukast (5) has been achieved starting from 2,4-dihydroxyacetophenone. The latter, on a Claisen condensation with ethyl oxalate, followed by hydrogenation, gave the chromane ester 7, which was subjected to a Fries rearrangement (AcOH/BF3·OEt2) and the product, after transesterification with methanol, was alkylated with 5-bromo-1-pentanyl acetate to afford the acetate 9. A novel methanolysis of 9 with methanol in the presence of tetra-n-butylammonium hydroxide followed by mesylation of the derived alcohol furnished the mesylate 10. Alkylation of the acetophenone derivative 16 with 10 using K2CO3 in the presence of tris(3,6-dioxaheptyl)amine and saponification gave 5.