Efficient synthesis of carbazoles via PtCl2-catalyzed RT cyclization of 1-(indol-2-yl)-2,3-allenols: scope and mechanism.

A detailed study on the scope of the efficient PtCl(2)-catalyzed synthesis of carbazoles from 1-(indol-2-yl)-2,3-allenols is described. Through isotopic labeling experiments, it is confirmed that the reaction proceeds through a unique metal carbene intermediate, which undergoes subsequent highly selective 1,2-hydrogen migration to afford carbazoles. The reaction shows wide scope and allows the introduction of a variety of different substituents at different positions on the carbazole due to the substituent-loading capability of both indole and the allene moiety.