Double N-arylation reaction of polyhalogenated 4,4’-bipyridines. Expedious synthesis of functionalized 2,7-diazacarbazoles

• Mohamed Abboud,
• Emmanuel Aubert and
• Victor Mamane

Beilstein J. Org. Chem. 2012, 8, 253–258, doi:10.3762/bjoc.8.26

• diffraction and show π–π stacking involving the diazacarbazole moieties and the phenyl rings of functionalized groups. Keywords: 4,4’-bipyridine; cross-coupling; crystal packing; diazacarbazole; X-ray diffraction; Introduction Only a few examples of the preparation of diazacarbazoles have been reported [1

• -diazacarbazole by using a palladium-catalyzed double N-arylation of 4,4’-dichloro-3,3’-bipyridine, itself obtained after a long reaction sequence [25][26][27]. In another patent, an intramolecular Buchwald–Hartwig amination [28][29] was used to generate a 2,7-diazacarbazole derivative in low yield [30]. Recently

• 2,7-diazacarbazole 3a showed a rather low reactivity of the C–Cl bonds in the 3- and 6-positions. Indeed, the Stille coupling [42] of 3a with 2-tributylstannylpyridine (8) afforded a mixture of mono- and di-functionalized compounds 9a and 9b in 40% and 33% yields, respectively. The Suzuki coupling [43