Synthesis of π-Extended Benzofulvenes: A Pd-Catalyzed Cascade Annulation Process Comprising C-C Bond Formation Followed by 1,6-Conjugate Addition

Design and Development of Carbene-Catalyzed Intramolecular Vinylogous Stetter Reaction to Access Phenanthrol Derivatives

The present study reveals the design and development of an N-heterocyclic carbene (NHC)-catalyzed intramolecular vinylogous Stetter reaction. This protocol enabled the synthesis of diverse phenanthrol derivatives and naphthol-fused heterocycles in very good to excellent yields. The success of the title reaction relies on the design of biaryl aldehydes bearing p-quinone methide (p-QM) moiety that acts as a vinylogous Stetter (1,6-conjugate) acceptor while the aldehyde functional group serves as an acyl anion equivalent, generated in situ from NHC-catalyzed umpolung. Salient features of the presented protocol include atom efficiency, operational simplicity, broad substrate scope, large-scale synthesis, and postsynthetic modifications.

Synthesis of 6H-Benzo[c]chromene Scaffolds: A Synthetic Strategy of Pd-Catalyzed Annulation Followed by Aerial Oxidation

A synthetic strategy of a palladium-catalyzed cascade annulation reaction followed by aerial oxidation was designed to construct 6H-benzo[c]chromene scaffolds. Various 6H-benzo[c]chromenes were synthesized under mild reaction conditions using easily accessible p-QMs and commercially available o-hydroxyarylboronic acids. One of the synthesized chromenes has been ambiguously confirmed by single-crystal XRD analysis. Interestingly, our synthesized 6H-benzo[c]chromenes could be easily transformed into valuable 6H-benzo[c]chromen-6-ones via aerial oxidation.

Synthesis and Photophysical Properties of 3-Substituted-1H-Indazoles: A Pd-Catalyzed Double C-N Bond Formation Strategy via 1,6-Conjugate Addition

A Pd-catalyzed cascade process for the direct synthesis of 3-substituted-1H-indazole employing p-quinone methide (p-QM) and arylhydrazine through Pd-catalyzed double C-N bond formation via 1,6-conjugate addition is reported. This reaction strategy affords efficient and practical access to synthetically important diverse 3-substituted-1H-indazoles in good yields. The photophysical properties of the synthesized 3-substituted-1H-indazoles are investigated, and some of them showed very good fluorescence properties with quantum yields up to 85%. Also, the synthesized 3-substituted-1H-indazole exhibits an acid-sensitive fluorescence turn-off activity.