The Reaction of Tropolones with Phosphorus Oxychloride. The Rearrangement Reaction of 5-Arylazo-2-chlorotropones to 2-Aryl-4, 5-dichloroindazoles

Abstract

Abstract The reaction of tropolone and phosphorus oxychloride gave 2-chlorotropone. Similarly, 5-cyano-, 5-nitro, and 5-chlorotropolones afforded the corresponding 2-chlorotropone derivatives in moderate yields. 3-Cyanotropolone gave 2-chloro-7-cyanotropone, while 3-phenyltropolone afforded only 2-chloro-3-phenylbenzaldehyde. When 3-bromotropolone and 5-bromotropolone were treated similarly, 2, 7-dichloro- and 2, 5-dichlorotropones were obtained respectively, with a facile halogen exchange. The further treatment of 2, 5-dichlorotropone with phosphorus oxychloride afforded 2, 5-dichloro- and 3,4-dichlorobenzaldehydes. The reaction of 5-p-tolylazo-, 5-phenylazo-, and 5-p-nitrophenylazotropolones with phosphorus oxychloride gave the corresponding 5-arylazo-2-chlorotropones, which, on further treatment with an excess of the reagent, gave 2-aryl-4, 5-dichloroindazoles.