Palladium-catalyzed regioselective arylation of imidazo[1,2-b][1,2,4]triazine: synthesis of an alpha 2/3-selective GABA agonist.

A convergent, practical, and efficient synthesis of 2',6-difluoro-5'-[3-(1-hydroxy-1-methylethyl)imidazo[1,2-b][1,2,4]triazin-7-yl]biphenyl-2-carbonitrile (1), an orally active GABA(A) alpha(2/3)-selective agonist, is described. The seven-step, chromatography-free synthesis was demonstrated on a multi-kilogram scale and utilized biaryl bromide 6 and imidazotriazine 22 as key intermediates. Biaryl bromide 6 was prepared via a highly selective aromatic bromination. The regioselective condensation of aminotriazine 15 with chloroacetaldehyde provided the desired imidazotriazine intermediate 22. A highly regioselective palladium-catalyzed arylation in the final step highlights the efficiency of the route.