3770-48-7

An efficient palladium-catalyzed tandem reaction for the one-pot synthesis of 9 H -carbazoles under microwave irradiation is developed. This approach involves a sequential Buchwald-Hartwig amination and a direct arylation from affordable and inexpensive anilines and 1,2-dihaloarenes. For the development of this purpose, a novel and magnetically recoverable palladium nanocatalyst supported on a green biochar under ligand-free conditions is used. Compared to other existing palladium-based protocols, the present synthetic methodology shows a drastic reduction in reaction times and excellent compatibility with different functional groups allowing to obtain a small library of 9 H -carbazoles in high yields and with good regioselectivity. This procedure represents the first example in the direct synthesis of carbazoles using a heterogeneous palladium nanocatalyst from commercial precursors. To examine the application of this protocol, a direct and scalable synthesis of the bioactive carbazole alkaloid clausenalene from commercially available starting materials is described.

No transition metals are necessary in the reaction of in situ generated arynes with nitrosoarenes to give substituted carbazoles. Depending on the fluoride source and the solvent, either N-arylated carbazoles or NH-carbazoles are obtained (see scheme; DME=dimethoxyethane, OTf=trifluoromethanesulfonate). In these cascades a C-C and one or two C-N bonds are formed. The reactions are easy to conduct and proceed under mild conditions. Copyright

One-pot synthesis of carbazoles from cyclohexanones and arylhydrazine hydrochlorides is disclosed. Various substituted carbazoles were obtained in moderate to good yields via a sequence of condensation, cyclization and dehydrogenation under metal free conditions using molecular oxygen as an oxidant.

Shedding light on azides: [Ru(TPP)CO] (TPP=tetraphenyl porphyrin dianion), white light and O2 were found to be a suitable catalyst combination to perform the annulation of several biaryl azides (see scheme). The high chemoselectivity of the process allows the synthesis of phenanthridines and dihydrophenanthridines in good yield and purity. Copyright

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The product from Fisher indole cyclization and dehydrogenation of cyclohexanone 2,4,6-trimethylphenylhydrazone (1) was determined to be 2,3,4-trimethylcarbazole (3) resulting from a formal 1,4-methyl migration, as previously proposed.To determine the destinations of migrating groups in these rearrangements, the Fischer indole cyclization and dehydrogenation of cyclohexanone 2-ethyl-6-methylphenylhydrazone (17) were studied.The products obtained were 1-ethylcarbazole, 1-methylcarbazole, 2-ethyl-1-methylcarbazole (18), and an apparent mixture of 1-ethyl-4-methylcarbazole (21) and 4-ethyl-1-methylcarbazole (22).However, no 1-ethyl-2-methylcarbazole (19), which would have been obtained by a "1,4"-methyl migration, was obtained.Analysis of the product ratios suggested that the apparent ethyl shift in formation of 18 actually proceeded by a formal shift of either an ethyl or a methyl group, followed by a ethyl shift.Cyclization of 3-pentanone 2,4,6-trimethylphenylhydrazone (26) proceeded to give the product of "1,4" methyl migration, demonstrating that such reactions can occur with phenylhydrazones of ketones other than cyclohexanone.It is proposed that steric factors play a major role in determining whether migrating groups undergo or "1,4" shifts during Fischer indole cyclizations.

It was found that the unexpected phenazines were formed as minor products by the low-temperature photolysis of 2,2'-diazidobiphenyls in a rigid matrix.The phenazine formation results from the 1,1-C-C bond fission of the biphenyl nucleus and suggests the aziridine intermediates.The low-temperature photolysis of 2-azido-2'-methylbiphenyl and 2-azido-2',4',6'-trimethylbiphenyl leads to the triplet-derived phenanthridine derivatives as major products.