One‐Pot Transition‐Metal‐Free Synthesis of Polysubstituted Fused Benzene Derivatives from Methyl Enol Ethers and Alkynes

Abstract

A mild and transition‐metal‐free one‐pot strategy is established to prepare polysubstituted naphthalene and phenanthrene derivatives from methyl enol ethers (MEE) with alkynes. Significantly, this protocol is promoted by boron trifluoride diethyl etherate (BF3⋅Et2O) at room temperature. A wide variety of diversely functionalized naphthalene and phenanthrene derivatives were obtained in good to excellent yields. A plausible mechanism involving a spiro quinonoid intermediate is proposed. Due to fluorescent nature of naphthalene, selected compounds were screened for the solvatochromism study. Notably, positive solvatochromism effect was observed in the case of nitro‐substituted naphthalene derivative (3 h) with respect to different polarity of solvents.