Partially fluorinated heterocyclic compounds. Part 18. Formation of Fischer indole products from acetophenone 1,3,4,5,6,7,8-heptafluoro-2-naphthylhydrazone and acetophenone pentafluorophenylhydrazone. The surprising loss of o-fluorine

Abstract

Acetophenone 1,3,4,5,6,7,8-heptafluoro-2-naphthylhydrazone (2) and acetophenone pentafluoro-phenylhydrazone (3) react in tetralin at reflux temperature to give among the products 4,5,6,7,8,9-hexafluoro-2-phenylbenz [e]indole (6) and 4,5,6,7-tetrafluoro-2-phenylindole (9) respectively; these are typical Fischer indole products, yet are formed by displacement of o-fluorine rather than o-hydrogen. The 2-naphthylamine (5) and 1,1′,2,2′,3,3′4,4′-octahydro-1,1′-bisnaphthyl (4) are also formed from (2), while ammonia, pentafluoro-N-(α-methylbenzylidene)aniline (8), 2,3,5,6-tetrafluoro-4-(1,2,3,4-tetrahydro-1-naphthyl)aniline (10) and the bisnaphthyl (4) are also formed from (3). Imine precursors are not the source of the cyclised compounds (6) and (9).