A two-step access to fused-/spiro-polycyclic frameworks via double Heck cascade and acid-driven processes

This report illustrates the rapid construction of two divergent classes of polycyclic frameworks, benzo[a]fluorenones and spiro-chromenone indenes, via a double Heck cascade and an acid-driven cyclization from easily accessible precursors, alkyl 2-bromocinnamate esters and diphenylacetylenes. The present strategy has surveyed a broad substrate scope and delivered an array of products with interesting structural features. Besides, fluorescence studies were performed for the synthesized benzo[a]fluorenones.

Brønsted/Lewis Acid-Promoted Site-Selective Intramolecular Cycloisomerizations of Aryl-Fused 1,6-Diyn-3-ones for Diversity-Oriented Synthesis of Benzo-Fused Fluorenes and Fluorenones and Naphthyl Ketones

Herein, a facile diversity-oriented approach to access functionalized benzo[a]fluorenes, benzo[b]fluorenones, and naphthyl ketones has been demonstrated via site-selective intramolecular cyclization of aryl-fused 1,6-diyn-3-ones. Synthesis of benzo[a]fluorenes and naphthyl ketones has been achieved selectively using TfOH and AgBF₄, respectively, via in situ-formed acetals. Aryl-fused 1,6-diyn-3-ones undergo triflic acid-mediated intramolecular cyclization, leading to benzo[b]fluorenone derivatives via a radical intermediate as supported by EPR studies. Kinetic studies of these transformations have also been performed by UV-visible spectroscopic analysis to shed light on the reaction profile.