Triphenylphosphine-mediated reductive cyclization of 2-nitrobiphenyls: a practical and convenient synthesis of carbazoles.
The synthesis of a series of substituted carbazoles from the corresponding 2-nitrobiphenyl derivatives using a novel modification of the Cadogan reaction is described. Cyclization of the 2-nitrobiphenyls was achieved via reductive deoxygenation of the nitro groups using a slight excess of triphenylphosphine in a suitable solvent. We have observed a temperature dependence on the extent of conversion under these conditions, with higher boiling solvents affording higher yields across a range of substrates. The new reaction conditions are very straightforward and convenient to execute, tolerate a broad range of functional groups, and yield carbazole products in the absence of unwanted side products.
Freeman
Adam W
AW
Eastman Kodak Company, Research and Development Laboratories, 1999 Lake Avenue, Rochester, NY 14650-2116, USA. adam.freeman@kodak.com
Urvoy
Marie
M
Criswell
Megan E
ME