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

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