NITRENIUM IONS .1. ACID-CATALYZED REACTIONS OF 2-METHYLINDOLE WITH NITROSOBENZENES - CRYSTAL-STRUCTURES OF 2-PHENYLAMINO-3-PHENYLIMINO-3H-INDOLE, 2-(O-TOLYLAMINO)-3-(O-TOLYLIMINO)-3H-INDOLE, N-PHENYL-N-(2-PHENYLAMINO-3H-INDOL-3-YLIDENE)AMINE N-OXIDE AND BIS(2-METHYL-1H-INDOL-3-YL)METHANE

2-Methylindole 3b reacts with nitrosobenzenes 1a-c in the presence of monochloroacetic acid affording compounds which are characterized by the formation of carbon-nitrogen bonds and other compounds which clearly could arise from a radical mechanism. The radical component of the reaction is also supported by the EPR spectroscopy as well as the reaction products distribution. Although these reactions cannot be considered of synthetic value for the number of isolated products, they could be regarded as clear examples of the electrophilic character and of the oxidative power of nitrogen in activated nitrosobenzenes. Crystal structures of 2-phenylamino-3-phenylimino-3H-indole 7a, 2-(o-tolylamino)-3-(o-tolylimino)-3H-indole 7b, N-phenyl-N-(2-phenylamino-3H-indol-3-ylidene)amine N-oxide 9a and bis(2-methyl-1H-indol-3-yl)methane 10 are also reported.