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.