Formal [4 + 1] Cycloadditions of β,β-Diaryl-Substituted <i>ortho</i>-(Alkynyl)­styrenes through Gold(I)-Catalyzed Cycloisomerization Reactions

Gold­(I)-catalyzed cycloisomerization of β,β-diaryl-<i>o</i>-(alkynyl)­styrenes at 80 °C selectively yields dihydro­indeno­[2,1-<i>a</i>]­indenes in a transformation that encompasses a formal [4 + 1] cycloaddition and takes place through a cascade 5-<i>endo</i>-cyclization–diene activation–<i>iso</i>-Nazarov cyclization. In addition, by performing the reaction at 0 °C, the same substrates exclusively give rise to benzofulvene derivatives, which have also been shown to be intermediates in the formation of the tetracyclics

Straightforward Synthesis of Dihydrobenzo[<i>a</i>]fluorenes through Au(I)-Catalyzed Formal [3 + 3] Cycloadditions

Dihydrobenzo[<i>a</i>]fluorene derivatives have been prepared by a formal intramolecular [3 + 3] cycloaddition of <i>o</i>-alkynylstyrenes bearing a secondary alkyl group at the β-position of the styrene moiety. The process, catalyzed by a cationic gold(I) complex, involves a 1,2-hydride migration as the key step. 6,11-Dihydro-5<i>H</i>-benzo[<i>a</i>]fluorenes could be obtained from the initially generated 6,6a-dihydro-5<i>H</i>-benzo[<i>a</i>]fluorenes by subsequent heating of the reaction mixture under gold(I) or Brønsted acid catalysis or directly by conducting the reactions at high temperature

Synthesis of Functionalized 1<i>H</i>‑Indenes and Benzofulvenes through Iodocyclization of <i>o</i>‑(Alkynyl)styrenes

A convenient method for the preparation of synthetically useful 3-iodoindene derivatives has been developed. This protocol, based on the 5-endo iodocyclization reaction of <i>o</i>-(alkynyl)­styrenes, represents one of the scarce examples of halocyclizations using olefins as nucleophilic counterparts and allows the synthesis of both 3-iodo-1<i>H</i>-indenes (from β-alkyl-β-alkyl/aryl-<i>o</i>-(alkynyl)­styrenes) and 3-iodobenzofulvenes (from β,β-diaryl-<i>o</i>-(alkynyl)­styrenes) in good yields under mild reaction conditions. In addition, related alkoxyiodocyclization processes are described, which are particularly interesting in their intramolecular version because they allow the synthesis of heteropolycyclic structures containing the indene core. Finally, the usefulness of the prepared 3-iodoindenes has been demonstrated by the synthesis of several polysubstituted indene derivatives through conventional palladium-catalyzed cross-coupling reactions and iodine–lithium exchange processes