Synthesis of fused-tetrahydropyrimidines: one-pot methylenation–cyclization utilizing two molecules of CO₂

A methylenation–cyclization reaction, employing cyclic enaminones with primary aromatic amines and two molecules of CO₂, furnishing fused-tetrahydropyrimidines, is discussed. In this Cs₂CO₃ and ZnI₂ catalyzed one-pot two-step procedure, two molecules of CO₂ were selectively converted to methylene groups. The multi-component reaction might proceed through the formation of bis(silyl)acetal which was followed by condensation and further aza-Diels–Alder reaction. Hydroquinazoline, hydrocyclopenta[d]pyrimidine and hydroindeno[1,2-d]pyrimidine derivatives could be prepared with CO₂ as the C1 source, effectively.