New Electrophilic Substitition of Azulene

Abstract

It is well known that azulene reactis with electrophiles at C-1 and C-3 position. Here we report new electrophilic substitution of azulene using trifluoaromethanesulfonic anhydride or trifluoromethanesulfonyl chloride as follows. The reaction of azulene with Tf₂O and pyridine N-oxide gave 1-(2-pyridyl)azulene in 45% yields. Without pyridine N-oxide, reaction did not proceed, but in the presence of triethylamine azulene reacted with Tf₂O to give 1-trifluoromethanesulfinylazulene instead of 1-Tf-azulene. Treatment of azulene with trifluroromethanesulfonyl chloride gave 1-chloroazulene in a poor yield. In the presence of LiCl, the yield of 1-chloroazulene increased. When tributhylammonium chloride was used instead of LiCl, same reaction proceeded. When tributhylammonium bromide was used, 1-bromoazulene was obtained as a main product. We will report reaction mechanisms of these interesting new electrophlic substitutions of azulene.