A Practical Synthesis of a Key Intermediate of Beraprost

A practical eight-step synthesis of a key intermediate of beraprost is described. The tricyclic cyclopent[b]benzofuran core can be prepared from 2,6-dibromo-4-chlorophenol. The butyric side chain is introduced by ortho-selective metal-halogen exchange and subsequent coupling with 4-(benzyloxy)butanal. The procedure is operationally simple and amenable to scale-up synthesis.