Synthesis of 3,4‐Dihydroquinazolinones via Base‐Promoted Formal [4 + 2] Cycloadditions

3,4‐dihydroquinazolin‐2( 1H )‐one (3,4‐DHQ) is a key structural motif found in many biologically active molecules. Although several synthetic methods have been developed to date, harsh reaction conditions, and/or metal toxic reagents are often required. In this work, a general, metal‐free methodology for the synthesis of 3,4‐DHQs is described. This novel protocol relies on a formal [4 + 2] cycloaddition of in situ formed aza‐ ortho ‐quinone methides and isocyanates leading to a wide variety of 3,4‐DHQs in yields up to 98%.