text: Alkynyl ethers and siloxyacetylenes have proven to be the ideal pair for aromatic annulations. The reactions can be run with both activated heterosubstituted alkynes and un-activated acetlyenes. Alkynyl thioethers and ynamines have been used as reactants in the annulation reaction.
  Conjugated enynes have also been used for benzannulation reactions catalyzed by cobalt. This type of benzannulation involves a [4+2] cycloaddition followed by a 1,3-hydrogen shift. In dichloromethane, the symmetrical benzannulation products are yielded but in tetrahydrofuran (THF), unsymmetrical benzannulation products were obtained with good regioselectivity.  These reactions utilize  1,3-bis(diphenylphosphino)propane (dppp) substituted cobalt catalyst in the presence of powdered zinc and zinc iodide for a solvent dependent benzannulation reaction (Scheme 11). In dichloromethane the ratio of A:B is 78:22 with an overall combined yield of 90% and in THF the ratio has switched to 7:93 (A:B) with a combined yield of 85%.
  Palladium-catalyzed benzannulations have been developed using allylic compounds and alkynes. This palladium catalyzed reaction has been performed in both inter- and intramolecular forms. The cationic palladium complex [(η-CH)Pd(CHCN)](BF) reacts with an excess of 4-octyne when heated to 80 °C in the presence of  triphenylphosphine forming the aromatic compound 1-methyl-2,3,4,5-tetrapropylbenzene (Scheme 12). It was determined that the presence of exactly one equivalent of palladium catalyst (from which the allyl group adds into the final aromatic structure) is crucial for the catalyzed benzannulation to occur in good yield.
  This catalyzed reaction was also optimized for allyl substrates with catalytic [Pd(dba)]CHCl and triphenylphosphine (dba =dibenzylideneacetone) (Scheme 13).