Synthesis of carbazoles
A palladium-catalyzed reaction sequence consisting of an intermolecular amination and an intramolecular direct arylation enabled highly regioselective syntheses of functionalized indoles or carbazoles and proved to be amenable to the use of inexpensive 1,2-dichloroarenes as electrophiles.
L. Ackermann, A. Althammer, P. Mayer, Synthesis, 2009, 3493-3503.
The iridium-catalyzed dehydrogenative cyclization of 2-aminobiphenyls proceeds smoothly in the presence of a copper cocatalyst under air as a terminal oxidant to yield N-H carbazoles. A similar catalytic system can also be used for a dimerization reaction of 2-aminobiphenyl involving 2-fold C-H/N-H couplings.
C. Suzuki, K. Hirano, T. Satoh, M. Miura, Org. Lett., 2015, 17, 1597-1600.
Various carbazoles can be synthesized from substituted biaryl azides at 60°C using Rh2(OCOC3F7)4 or Rh2(OCOC7H15)4 as catalysts.
B. J. Stokes, B. Jovanović, H. Dong, K. J. Richert, R. D. Riell, T. G. Driver, J. Org. Chem., 2009, 74, 3225-3228.
A Pd(II)-catalyzed C-H bond amination reaction operates under extremely mild conditions and produces carbazole products in good to excellent yields. Carbazoles possessing complex molecular architecture can also be formed using this reaction, highlighting its potential in natural product synthesis applications.
J. A. Jordan-Hore, C. C. C. Johansson, M. Gulias, E. M. Beck, M. J. Gaunt, J. Am. Chem. Soc., 2008, 130, 16184-16186.
An intramolecular palladium(II)-catalyzed oxidative carbon-carbon bond formation under air in the presence of pivalic acid as the reaction solvent, instead of acetic acid, results in greater reproducibility, higher yields, and broader substrate scope. The reaction allows the conversion of both electron-rich and electron-deficient diarylamines.
B. Liégault, D. Lee, M. P. Huestis, D. R. Stuart, K. Fagnou, J. Org. Chem., 2008, 73, 5022-5028.
A palladium-catalyzed tandem directed C-H functionalization and amide arylation gave a series of substituted carbazoles. The Pd(0) species generated are reoxidized to Pd(II) in the presence of Cu(OAc)2 and an atmosphere of oxygen.
W. C. P. Tsang, N. Zheng, S. L. Buchwald, J. Am. Chem. Soc., 2005, 127, 14560-14561.
An efficient route to carbazoles and dibenzofurans has been developed. The reaction of o-iodoanilines or o-iodophenols with silylaryl triflates in the presence of CsF to afford N- or O-arylated products is followed by a cyclization using a Pd catalyst to carbazoles and dibenzofurans in good to excellent yields. Various functional groups are tolerated.
Z. Liu, R. C. Larock, Org. Lett., 2004, 6, 3739-3741.
NH4I promotes an efficient indole-to-carbazole strategy under metal-free conditions. The reaction offers high regioselectivity through formal [2 + 2 + 2] annulation of indoles, ketones, and nitroolefins and enables the assembly of a large number of diversified carbazoles with good functional group tolerance.
S. Chen, Y. Li, P. Ni, H. Huang, G.-J. Deng, Org. Lett., 2016, 18, 5384-5387.
Either spirocyclic indolenines or carbazoles can be generated from a common indole-tethered propargyl alcohol precursor in high yields upon treatment with different Ag(I) catalysts at rt. An unexpected hydration reaction to afford (±)-actinopolymorphol B is also reported.
M. J. James, R. E. Clubley, K. Y. Palate, T. J. Procter, A. C. Wyton, P. O'Brien, R. J. K. Taylor, W. P. Unsworth, Org. Lett., 2015, 17, 4372-4375.
A sequential cascade process for the synthesis of iodocarbazoles through a tandem iodocyclization with migration and aromatization can be conducted at room temperature and in a short time.
J. Wang, H.-T. Zhu, Y.-F. Qiu, Y. Niu, S. Chen, Y.-X. Li, X.-Y. Liu, X.-M. Liang, Org. Lett., 2015, 17, 3186-3189.
AuCl3-catalyzed cyclizations of 1-(indol-2-yl)-3-alkyn-1-ols occurred smoothly in toluene at room temperature leading to a series of carbazole derivatives efficiently. A possible mechanism has been proposed.
Y. Qiu, W. Kong, C. Fu, S. Ma, Org. Lett., 2012, 14, 6198-6201.
A gold(I)-catalyzed intramolecular hydroarylation of (Z)-2-(enynyl)indoles gives carbazoles in good yields. The requisite (Z)-2-(enynyl)indoles were synthesized stereoselectively by trimethylgallium-promoted, Z-selective Wittig olefination of N-alkylindole-2-carboxaldehydes with propargyl ylides.
C. Praveen, P. T. Perumal, Synlett, 2011, 268-272.