CARBAZOLE SYNTHESIS VIA AN IN-SITU TRAPPING STRATEGY WITH INDOLYL ENOL ETHERS

Indolyl enol ethers, generated from the alkoxy(indolyl)carbenium tetra fluoroborates 1 by treatment with sodium hydride, can be trapped with dimethyl acetylenedicarboxylate or N-phenylmaleimide to furnish the se lectively functionalized carbazoles 3, 4, 5, 9, 10, and 13. In additio n, the biaryl derivatives 6 and 11 are produced by a ring-opening reac tion of the primarily formed Diels-Alder adduct. In the case of the bi aryl derivative 6, an X-ray crystal structure analysis yields valuable information on constitutions and configurations in the biaryl series. The phenomenon of atropisomerism is discussed for this compound.