Synthesis of Cyclobutene-Fused Indolines through (2 + 2) Cycloaddition of 4-Substituted Indoles and 2-Alkynyl Quinazolinones

Herein, a variety of cyclobutene-fused indolines bearing vicinal stereocenters were prepared in moderate to excellent yields (25%–93%) through Brønsted acid and hexafluoroisopropanol (HFIP)-cocatalyzed (2 + 2) cycloaddition of 4-substituted indoles with 2-alkynyl quinazolinones under mild reaction conditions. Experimental results revealed that HFIP might play important roles on the reaction efficiency through the hydrogen bonding effect. More importantly, a chiral cyclobutene-fused indoline could be achieved by chiral Brønsted acid catalyst. The present method features mild reaction conditions, organocatalyzed (2 + 2) cycloaddition, and novel quinazolinone-derived cyclobutene-fused indolines.