A modified Biginelli reaction toward oxygen-bridged tetrahydropyrimidines fused with substituted 1,2,4-triazole ring

A microwave-assisted Biginelli-like three-component condensation using salicylic aldehyde derivatives, acetone, and 5-substituted 3-amino-1,2,4-triazoles instead of the urea component results in the formation of oxygen-bridged tetrahydrotriazolopyrimidine derivatives (11,12-dihydro-5,11-methano[1,2,4]triazolo[1,5-c][1,3,5]benzoxadiazocines) in good yields and high purity. A plausible reaction mechanism for this transformation is discussed in details using literature and experimental data.