Highly palladium catalyzed chemoselective domino reaction: a practical way to the synthesis of 6H-benzo[c]chromenes and spiro[benzo[c]chromene-6,2′-chroman]s

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.

Visible light mediated synthesis of 6H-benzo[c]chromenes: transition-metal-free intramolecular direct C-H arylation

A synthetic approach towards the 6H-benzo[c]chromene ring under visible light and transition-metal-free conditions has been developed. Benzochromenes are synthesized from the corresponding (2-halobenzyl) phenyl ethers or (2-halophenyl) benzyl ethers using KO^tBu in dimethyl sulfoxide (DMSO) at room temperature (rt) and blue light-emitting diodes (LEDs) as the light source. This methodology replaces the use of ligands or additives, high temperatures and toxic solvents. The photostimulated reaction exhibits very good tolerance to different functional groups and 5H-dibenzo[c,f]chromenes are also effectively obtained. An electron donor-acceptor complex formed by the dimsyl anion and (2-halobenzyl) phenyl ethers was found and it induces the ET as the initial step in the photocyclization reaction. Furthermore, in order to explain the regiochemical outcome of this reaction, a theoretical analysis was performed using DFT methods.

Synergistic silver/scandium catalytic spiroketalization of β-alkynyl ketones for the atom economical synthesis of skeletally diverse spirocyclic isochromenes

Two types of new synergistic silver/scandium catalytic spiroketalizations of β-alkynyl ketones have been achieved, delivering a variety of skeletally diverse spirocyclic isochromenes in generally good yields.

Synergistic silver/scandium catalysis for divergent synthesis of skeletally diverse chromene derivatives

The combination of AgTFA and Sc(OTf)₃ enables the bimetallic synergistic catalysis of β-alkynyl ketones and o-hydroxybenzyl alcohols, allowing divergent synthesis of three classes of skeletally diverse chromene derivatives with generally high diastereoselectivity through dehydroxylated bi- and tri-cyclization cascades.