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

Abstract

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.