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

Mohamed Abboud,Emmanuel Aubert,Victor Mamane

doi:10.3762/bjoc.8.26

Abstract

Unusual 2,7-diazacarbazoles were prepared in one step from readily available tetra-halogenated 4,4’-bipyridines by using a double N-arylation reaction in the presence of the Pd–XPhos catalyst system. Moderate to good yields were obtained in this site-selective Buchwald–Hartwig double amination. The functionalization of these tricyclic derivatives was performed by using Pd-catalyzed cross-coupling reactions such as the Stille and Suzuki couplings. Two compounds were analyzed by X-ray diffraction and show π–π stacking involving the diazacarbazole moieties and the phenyl rings of functionalized groups.

Highlights

A few examples of the preparation of diazacarbazoles have been reported [1,2,3,4,5] and up to date no general method is available in the literature
One example was found in a patent concerning the synthesis of 3,6-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]
Whereas 3b crystallizes with one molecule per asymmetric unit in space group C2/c, the more functionalized 12c diazacarbazole is described by the less symmetric P−1 space group with two crystallographically independent molecules. In both compounds the crystal packing is governed by π–π stacking, forming infinite columns in which molecules interact through diazacarbazole moieties

Summary

Introduction

A few examples of the preparation of diazacarbazoles have been reported [1,2,3,4,5] and up to date no general method is available in the literature. One example was found in a patent concerning the synthesis of 3,6-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]. Scheme 2: Ligand effect in the double N-arylation of 2a with 6a.

Results

Conclusion