Cycloisomerization – a straightforward way to benzo[h]quinolines and benzo[c]acridines
Cycloisomerization of 3-alkynyl-2-arylpyridines and quinolines offers a straightforward approach to benzo[h]quinolines and benzo[c]-acridines. Substituent at the triple bond governs a choice between transition metal or Brønsted acid catalysis. A direct electrophilic activation by trifluoromethanesulfonic acid induces an almost quantitative cyclization of the o-aryl(phenylethynyl) fragment. PtCl2 efficiently catalyzes cyclization of 2-aryl-3-ethynylhetarenes.