Iron-Catalyzed Tandem Conia–Ene/Friedel–Crafts Reactions of o-Alkynyldihydrochalcones: Access to Benzo[b]fluorenes

Abstract

o-Alkynyldihydrochalcones when treated with a catalytic amount of anhydrous FeCl3 in refluxing 1,2-dichloroethane underwent tandem Conia-ene and Friedel-Crafts reactions to yield benzo[b]fluorene derivatives in good yields.

Fe‐Catalyzed Cycloisomerizations

“…More recently, Srinivasan and Akbar developed a tandem Conia‐ene/Friedel‐Crafts reaction of o ‐alkynyldihydrochalcones to benzo[ b ]fluorenes by using 30 mol % FeCl 3 as the catalyst …”

Iodine-mediated synthesis of benzo[a]fluorenones from yne-enones

“…While exploring the synthetic potentials of o -alkynylchalcones, 8 we discovered that related yne-enones 1 when heated under reflux with iodine in AcOH gave benzo[ a ]fluorenones 2 through a cascade process ( Scheme 1 , eqn (1)). It is worthwhile to compare these results with Hu's work, 9 in which chalcones 1 have been converted into benzo[ b ]fluorenols 3 by a Pd-catalyzed intramolecular dehydroaromatization and carbonyl reduction sequence ( Scheme 1 , eqn (2)) and also with Li's work, 10 in which chalcones 1 have been transformed into 1,4-naphthoquinones 4 by a Cu-catalyzed intramolecular oxidative 6- endo-trig cyclization ( Scheme 1 , eqn (3)).…”