ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Transition metal-catalyzed N-atom transfer reactions of azides provide efficient ways to construct new carbon–nitrogen and sulfur–nitrogen bonds. These reactions are inherently green: no additive besides catalyst is needed to form the nitrenoid reactive intermediate, and the by-product of the reaction is environmentally benign N2 gas. As such, azides can be useful precursors for transition metal-catalyzed N-atom transfer to sulfides, olefins and C–H bonds. These methods offer competitive selectivities and comparable substrate scope as alternative processes to generate metal nitrenoids.

An array of carbazoles (23 examples) can be synthesized from substituted biaryl azides at 60 °C using substoichiometric quantities of Rh 2 (O 2 CC 3 F 7 ) 4 or Rh 2 (O 2 CC 7 H 15 ) 4 .A long-standing goal of organic synthesis is the development of new methods that access nitrogen heterocycles, 1 such as carbazoles, because of their prevalence in important medicinal compounds and materials. 1,2 Historically, methods that access these N-heterocycles have relied on transformations of pre-existing functional groups, such as halides or carbonyls. 3 Such prerequisites can lead to an increased number of synthetic steps necessary to generate the starting materials. Recent efforts to circumvent this functional group manipulation have produced carbazoles through transition metal-mediated oxidative C-H bond functionalization. [4][5][6][7][8] Dirhodium(II) complexes are well known atom-transfer catalysts. 9 They are particularly effective in aliphatic C-N bond formation, 10 enabling access to nitrogen heterocycles efficiently and stereoselectively by the decomposition of sulfonyliminoiodinanes 11,12 and Ntosyloxycarbamates. 10c,f Employing azides as substrates would complement these existing technologies as well as related deoxygenation methods, 13,14 as azides are easily obtained, 15 intrinsically prone to decomposition, 16,17 and produce N 2 as the only by-product. Despite the proclivity of rhodium(II) dimers to mediate atom transfer reactions, 10 their use in the decomposition of azides is uncommon. 18,19 We reported recently that rhodium(II) carboxylates can catalyze the intramolecular formation of C-N bonds from vinyl-or aryl azides to provide indoles and pyrroles. 20 We envisioned that our method might be extended to biaryl azides for the synthesis of carbazoles. The requisite biaryl azides (3) were synthesized from 2-bromoaniline 1 by a Suzuki crosscoupling reaction 21 followed by a diazotization/azidation sequence 15,22 (Scheme 1). We found that substoichiometric quantities of rhodium(II) perfluorobutyrate or rhodium(II) octanoate efficiently generated the desired carbazole 5 from 2-azidobiphenyl (method A or B). 23 As before, crushed 4 Å molecular sieves (100 wt %) were required to achieve reproducible yields.To examine the scope and limitations of the reaction, we tested our method on substrates, which varied the electronic-and steric environments on each ring of the azidobiaryl. As shown in tgd@uic.edu. Table 1, electron-donating groups and electron-withdrawing groups were well tolerated for R 1 (entries 1 -6). The reaction could be performed on a gram-scale: 3.17 mmol of bromosubstituted biaryl azide 6f was converted smoothly to the corresponding carbazole in 85% yield. In contrast to the nearly uniform reactivity of substrates 6a -6f, we found that carbazole formation depended more strongly on the electronicand steric identity of the R 2 -, R 3 -, or R 4 -substituent. Electron-deficient R 2 -groups (e.g. F and Cl, entries 8 and 9) were high yielding, whereas reduced conversion and yield were observe...

Azides to indoles: Dirhodium(II)‐catalyzed decomposition of aryl azides was developed as a mild, functional group tolerant method for the synthesis of indoles (see scheme).

General considerations. All manipulations were carried out in the inert atmosphere provided by a nitrogen-filled glove box. 2,2,2-Trifluoroethanol-d 3 (TFE-d 3 , Cambridge Isotopes) was dried with 3 Å mol sieves, which had been pretreated with acetone-d 6 and activated at 150°C under dynamic vacuum prior to vacuum distillation. Methylene chloride-d 2 , benzene-d 6 , pxylene-d 10 , mesitylene-d 12 (Cambridge Isotopes), acetonitrile, benzene, p-xylene, mesitylene (OMNI Solv), and tris(pentafluorophenyl)borane (Strem) were used as received without further purification. (NN)PtMe 2 (NN = 2,3-bis(3,5-dimethylphenylimino)butane) was prepared by the previously reported procedure and gave satisfactory analyses, which were performed at Midwest Microlab, LLC.