Isolation and synthesis of biologically active carbazole alkaloids

Photocyclization of Stilbenes and Related Molecules

Three classes of ligands, designed to explore the effect of variations on the central pyridine donor core in bis(imino)pyridine iron and cobalt ethylene polymerization catalysts of the general formula [LMCl(2)] (M = Fe or Co), have been prepared. The first class comprises six-membered N-heterocycles (pyrimidine and triazine) and the second class five-membered heterocycles (furan and thiophene) as the central donor core. In the third class of ligands, the imine donor arm has been extended by one carbon to give anionic tridentate ligands based on carbazole and neutral analogues based on dibenzofuran and dibenzothiophene. The coordination behavior of these ligands upon reaction with FeCl(2) or CoCl(2) has been investigated, whereby only in the case of the neutral pyrimidine or the anionic carbazolide unit as the central donor core have stable complexes been obtained. Ethylene polymerization results are compared with the parent bis(imino)pyridine iron and cobalt catalyst systems.

Iron and Cobalt Ethylene Polymerization Catalysts: Variations on the Central Donor

Publisher Summary This chapter focuses on the chemistry of carbazoles. The reactions of the nucleus, introduction of substituents on carbazole nitrogen, reactions involving n-substituents, introduction of substituents onto carbazole carbon, and reactions involving c-substituents, outline the chemical properties of the carbazoles. The chapter also describes the methods for the synthesis of carbazoles. The method that has been most utilized for the preparation of aromatic carbazoles from noncarbazole precursors is the dehydrogenation of a tricyclic indole, usually a 1, 2, 3, 4-tetrahydrocarbazole. In addition, precursors such as biphenyls with an ortho nitrogen substituent, the diphenylamines, two separate six-membered ring components, and indoles are used for the synthesis of carbazoles.

Recent advances in the chemistry of 9H-carbazoles

A series of three derivatives of 1,8-di(pyrid-2'-yl)carbazole were prepared by Stille-type coupling of 2-(tri-n-butylstannyl)pyridine with the appropriate 1,8-dibromocarbazole. The carbazoles were prepared by appropriate substitution methodologies on the parent carbazole or by palladium-catalyzed cyclization of di-(p-tolyl)amine to provide the carbazole ring system. An X-ray structure of the di-tert-butyl derivative confirmed that both pyridyl groups were oriented for favorable intramolecular H-bonding to the central N-H. Two orientations of the molecule were found in the unit cell and this observation was corroborated by two N-H stretching bands in the solid state IR. Substitution of N-H by N-D led to increased emission intensity through diminished intramolecular deactivation of the excited state. The di-tert-butyl derivative formed a tridentate complex with Pd(II), which showed a red-shifted band attributed to an intraligand charge transfer state.

Preparation and study of 1,8-di(pyrid-2'-yl)carbazoles.

The product of photolysis of di-p-tolyamine in petroleum ether is 3,6-dimethylcarbazole. The primary product of gas-phase thermolysis of di-p-tolylamine at 850–1000°/0.01–0.05 Torr is also 3,6-dimethylcarbazole. In the higher temperature range monomethylcarbazole and carbazole are also formed. Thermolysis of tetra-p-tolylhydrazine at 800–1000° gives only di-p-tolylamine, the latter decomposing further in the higher temperature range. It is concluded that carbazole formation involves in both cases an electrocyclization of the ortho-positions, and not a rearrangement, and that diphenylaminyl is not an intermediate.

M. Gaugaz

Papers

On the Mechanism of the Thermal and Photolytic Cyclization of Diphenylamines to Carbazoles