Three-Component Coupling of Aromatic Aldehydes, 1‑Morpholino-2-nitroalkenes, and 3‑Aminoazoles via Boron Trifluoride Etherate Catalysis: Reaction Pathway and Features of the Formation of Intermediates

4,7-Dihydro-6-nitro-7-Ar-5-R-azolo­[1,5-a]­pyrimidines were obtained by the multicomponent reaction
of aminoazoles, morpholino-nitroalkenes, and aromatic aldehydes in
the catalysis of boron trifluoride etherate. The optimal reaction
conditions were determined, and the formation of the target regioisomer
was demonstrated. The pathway for multicomponent transformation, including
the formation of azolyl-nitroalkene, was determined. Morpholino-nitroalkenes
were assumed to convert into the corresponding nitroalkynes during
catalysis of boron trifluoride etherate. For a multicomponent reaction
with 4-nitrobenzaldehyde, conditions have been proposed that exclude
the formation of a side regioisomer.