Controllable Chemoselectivity Cascade Reactions for the Synthesis of Phenanthrenols via Palladium-Catalyzed-Suzuki/Heck Reaction and Michael Addition.

Palladium serves as a multi-functional catalyst which is controllable by tuning reaction conditions. This work demonstrated the utilization of a palladium catalyst for the synthesis of phenanthrenols by cascade palladium-catalyzed Suzuki/Heck reaction between chalcone and 2-bromophenylboronic acid, followed by Michael addition. The sequential reaction could be controlled by reactivity of the palladium catalyst in different solvents and concentrations of reagents. This protocol could be applied to a broad range of substrates to give products in low to good yields.

Selective electrophilic cyclization of ortho-carbonylarylacetylenols for the synthesis of cyclopenta[a]naphthalenol and 2-phenylnaphthalen-1-ol analogs.

This work demonstrates a new method for the synthesis of cyclopenta[a]naphthalenol and 2-phenylnaphthalen-1-ol analogs via selective cyclization. ortho-Alkynylarylkenones were employed as the common substrates that could be prepared by Sonogashira coupling between 2-haloarylacetophenone and pent-4-yn-1-ol derivatives. These precursors were used without purification to construct 2-phenylnaphthalen-1-ol intermediates by treating with (+)-CSA under heating conditions. Selective cyclization occurred when the reaction was conducted in methyl trimethylacetate solvent which predominantly produced the 2-phenylnaphthalen-1-ol product through 6-endo-dig cyclization without elimination or the formation of cyclopenta[a]naphthalenol via shutting down the 5-exo-dig mode of cyclization. Switching the acid from a Brønsted acid to Bi(OTf)3 led to smooth reactions, providing the cyclopenta[a]naphthalenol products in moderate to good yields. Moreover, we also demonstrated the utilization of 2-phenylnaphthalen-1-ol to prepare naphthoquinone, which is an important core structure of bioactive and natural product compounds.