Ammonium tetrafluoroborate: Novel Unprecedented Catalyst for the Synthesis of 3,4-dihydropyrimidin-2(1H)-ones through Biginelli Reaction

A novel method has been developed to use ammonium tetrafluoroborate (NH4BF4) directly as catalyst in Biginelli reaction. A new paradigm of the Biginelli reaction for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones derivatives found the use of ammonium tetrafluoroborate as a novel, inexpensive, readily available, non-toxic and mild catalyst in good to excellent yields. Notably, this is the first time that ammonium tetrafluoroborate is directly used as a catalyst in organic synthesis. So far, no organic reaction is available in literature where NH4BF4 is directly used as catalyst. However, some reactions are found where NH4BF4 is used with other catalysts as promoters or additives. The protocol developed has several advantages, such as highly efficient, simple, atom-economical, environmentally friendly, easy synthetic and purification methods.