Organocatalytic and enantioselective [4+2] cyclization between hydroxymaleimides and ortho-hydroxyphenyl para-quinone methide-selective preparation of chiral hemiketals

A cinchona alkaloid squaramide promoted enantioselective [4+2] cyclization between hydroxymaleimides and ortho-hydroxyphenyl p-QMs has been disclosed, and a wide range of chiral hemiketals containing chromane and succinimide frameworks with two adjacent quaternary stereogenic centers have been prepared for the first time with excellent results (up to 99% yield, up to 99 : 1 dr, up to >99% ee) under mild conditions.