Reactions of complex ligands .70. An intramolecular alkyne insertion/carbonylation/cyclization sequence of chromium aminocarbene complexes: A novel access to indole and indenoindole skeletons

2-Alkynylanilinocarbene chromium complexes 1-7 bearing a rigid arene C-2 spacer between the aminocarbene and alkyne units were prepared from pentacarbonyl(aroyl)chromates(-I), acetyl bromide, and 2-alkynylanilines. They undergo intramolecular cyclization the course of which depends on the substitution pattern at the alkyne terminus. A tandem alkyne insertion into the metal-carbene bond/carbonylation sequence affords Cr(CO)(3)-coordinated 5-indolylketenes 8, 9, 12-14 by using a bulky substituent; the rate of the reaction increases with N-alkylation. Less bulky n-alkynylanilinocarbene complexes 4, 5 exhibit two competing carbene annulation sequences: Benzannulation leads to benzo[a]carbazoles 15, 16, whereas cyclopentannulation without prior carbonylation furnishes indeno[1,2-b]indoles 17, 18.