Phenanthrene synthesis by iron-catalyzed [4 + 2] benzannulation between alkyne and biaryl or 2-alkenylphenyl Grignard reagent

Article abstract of DOI:10.1021/ja201931e

The [4 + 2] benzannulation reaction of internal or terminal alkynes with 2-biaryl, 2-heteroarylphenyl, or 2-alkenylphenyl Grignard reagents in the presence of Fe(acac)₃, 4,4′-di-tert-butyl-2,2′-bipyridyl, and 1,2-dichloro-2-methylpropane takes place at room temperature in 1 h to give 9-substituted or 9,10-disubstituted phenanthrenes and congeners in moderate to excellent yields. The reaction tolerates sensitive functional groups such as bromide and olefin. When applied to a 1,3-diyne, the annulation reaction takes place on both acetylenic moieties to give a bisphenanthrene derivative.