Organocatalytic [4 + 2] cyclizations of para-quinone methide derivatives with isocyanates

The first [4 + 2] cyclizations of para-quinone methide derivatives with isocyanates have been established under the catalysis of Brønsted acids or Brønsted bases, which efficiently constructed benzoxazin-2-one frameworks in generally high yields (up to 95%). This reaction will not only enrich the research contents of para-quinone methide-involved cyclization reactions but also provide a useful method for constructing biologically important benzoxazin-2-one frameworks.