New synthesis of 9-methanesulfonyl-1,2,3,9a-tetrahydro- and 1,2,3,4-tetrahydrocarbazoles from N-methanesulfonyl-2-(cyclohex-1-enyl)aniline

The reaction of N-methanesulfonyl-2-(cyclohex-1-en-1-yl)aniline with Br₂ in the presence of NaHCO₃ in MeCN results in N-methanesulfonyl-2-(6-bromocyclohex-1-en-1-yl)aniline, which was cyclised to 9-methanesulfonyl-1,2,3,4-tetrahydrocarbazole, and the effect of NH₃ leads to 9-methanesulfonyl-1,2,3,9a-tetrahydrocarbazole. The reaction of the latter with molecular bromine in the presence of pyridine results in 1-(9-methanesulfonyl-1,2,3,4-tetrahydro-4-carbazolyl)pyridinium bromide in a good yield.