The Suzuki-Miyaura Cross-Coupling Reactionsof 2-, 6- or 8-Halopurines with Boronic Acids Leading to 2-, 6- or 8-Aryl- and -Alkenylpurine Derivatives

The Suzuki-Miyaura cross-coupling reactions of 9-benzyl-6-chloropurine, 9- or 3-benzyl-8-bromoadenine and 2,6-dihalopurines with boronic acids gave the corresponding 6-, 8- or 2-aryl- or -alkenylpurines in good yields. Anhydrous conditions in toluene were superior for coupling of electron-rich boronic acids, while aqueous DME was used for electron-poor arylboronic acids as well as for alkenylboronic acids. A good regioselectivity was observed for the coupling of 2,6-dihalopurines: 9-benzyl-2,6-dichloropurine reacted with one equivalent of phenyl boronic acid to give 9-benzyl-2-chloro-6-phenylpurine, while an analogous reaction of 9-benzyl-6-chloro-2-iodopurine gave selectively 9-benzyl-6-chloro-2-phenylpurine.