Reactivities of heteroaromatic cations containing a Group VIB element in nucleophilic reactions. Reactions of 9-phenyl-xanthylium, -thioxanthylium, and -selenoxanthylium salts with amines, sodium phenolate, and sodium benzenethiolate

Abstract

Reactions of 9-phenylchalcogenoxanthylium salts (1a–c) with some nucleophiles have been examined in order to find the differences in reactivity in nucleophilic reactions. The chalcogenoxanthylium salts (1a–c) react with aniline in ether to give 9-anilino-9-phenylchalcogenoxanthenes (7a–c). However, in acetonitrile the xanthylium salt (1a) affords N,4-bis(9-phenylxanthen-9-yl)aniline (9a) together with the anilinoxanthene (7a)(at room temperature) or 9-(p-aminophenyl)-9-phenylxanthene (8a)(at reflux) and the sulphur (1b) and the selenium derivative (1c) affords only the anilino derivatives (7b,c), respectively.

In the reactions with sodium phenolate, the thioxanthylium salt (1b) gave 9-phenoxy-9-phenylthioxanthene (13b), whereas the oxygen (1a) and the selenium congener (1c) gave O,4-bis(9-phenylchalcogenoxanthen-9-yl)phenols (15a,c) together with the 9-phenoxy derivatives (13a,c), respectively.

The results show that the thioxanthylium salt (1b) gave the products formed on attack by the heteroatom of the ambident nucleophiles and the ratio of the carbon attack increased in the order (1a) > (1c) > (1b). This difference would be attributable to the properties of carbocations at the 9-position in the heteroaromatic cations (1a–c).