[2+2+1+1] Cycloaddition Reaction of 1,3,5‐Triazinanes with Methylene Compounds: Approach to Hexahydropyrimidines

Abstract An acetic acid‐catalyzed [2+2+1+1] cycloaddition of 1,3,5‐triazinanes with methylene compounds was developed. This protocol provides an access to hexahydropyrimidines (HHPs) (25 examples) in 35–99% yields under mild conditions in 2 hours. The potential application of this method was demonstrated by gram‐scale synthesis. Preliminary mechanistic investigation was conducted to elucidate the possible mechanism. This work represents the yet unknown example of [2+2+1+1] cycloaddition reaction between 1,3,5‐triazinanes and active methylene compounds.