A stereospecific synthesis of the drug-candidate 1 is described. The synthetic sequence, aimed at accomplishing modularity and cost savings, features a series of organometallic steps to afford stereospecifically the desired trisubstituded olefin active pharmaceutical ingredient. Key developments consist of a mild Sonogashira reaction of aryl bromide 7a with the polymerization prone propargyl alcohol and a stereospecific hydroalumination, Zn/Al exchange, and Pd-catalyzed cross-coupling sequence facilitated by the commercially available PEPPSI catalyst.

Abstract:The carboxylate anion has been used as a directing group in the aromatic amination of electronically equivalent aryl bromides to afford selective ortho-substituted derivatives (> 99:1 selectivity; 60-80% yield) in the case of copper(I) catalysis. The solvent, base and equivalents of base were important factors in the success of this reaction. Complementary selectivity was achieved with palladium catalysis where the para-substituted derivatives were produced selectively (> 99% selectivity, 70-80% yield).