Phosphine-Catalyzed (4 + 1) Annulation of <i>o</i>‑Hydroxyphenyl and <i>o</i>‑Aminophenyl Ketones with Allylic Carbonates: Syntheses and Transformations of 3‑Hydroxy-2,3-Disubstituted Dihydrobenzofurans and Indolines

A phosphine-catalyzed (4 + 1) annulation reaction of <i>o</i>-hydroxyphenyl and <i>o</i>-aminophenyl ketones with ester-modified allylic carbonates has been developed, providing a facile and efficient method to synthesize functionalized 2,3-disubstituted dihydrobenzofurans and indolines. Under mild conditions and in the catalysis of PPh₃ (20 mol %), the reactions of <i>o</i>-hydroxyphenyl or <i>o</i>-aminophenyl ketones readily furnish highly functionalized 3-hydroxy-2,3-disubstituted dihydrobenzofurans or 3-hydroxy-2,3-disubstituted indolines in 40–99% yields with generally high diastereoselectivity. To further expand the utility of this annulation reaction to the synthesis of functionalized benzofurans and indoles, the CuSO₄-promoted chemical transformations of the annulation products have also been studied