Features of the Synthesis of 3‐(1,2,4‐Triazolyl)‐Coumarins by the Knoevenagel Reaction

Abstract Peculiarities of the synthesis of 3‐(1,2,4‐triazol‐3‐yl)coumarins starting from 2‐(1 H ‐1,2,4‐triazol‐3‐yl)acetonitriles or ethyl 2‐(1 H ‐1,2,4‐triazol‐3‐yl)acetates derivatives and salicylic aldehydes are described. New representatives of 3‐(1,2,4‐triazol‐3‐yl)coumarins are fully characterized using MS spectrometry, 1 H and 13 C NMR, and IR spectroscopy. It was found that formation of coumarins from N‐substituted 2‐(1 H ‐1,2,4‐triazol‐3‐yl)acetonitriles and ethyl 2‐(1 H ‐1,2,4‐triazol‐3‐yl)acetates undergoes in two and one step, correspondingly. The presence of NH‐triazole at the 3rd position of iminocoumarin, formed in the first step from 2‐(1 H ‐1,2,4‐triazol‐3‐yl)acetonitriles, allows it to further condense with salicylaldehydes to form a triazolopyrimidine system annulated to a chromene core of two types (5 H ‐ or 12 H ‐chromeno[3,2‐ e ][1,2,4]triazolo[1,5‐ c ]pyrimidine), whilst analogous 2‐(1 H ‐1,2,4‐triazol‐3‐yl)acetate produce title 3‐(1 H ‐1,2,4‐triazol‐3‐yl) coumarin. The crystal structure of one 5 H ‐chromeno[3,2‐ e ][1,2,4]triazolo[1,5‐ c ]pyrimidine derivative was confirmed by X‐ray analysis. The reactivity of 7‐hydroxy‐3‐(1,2,4‐triazol‐3‐yl)coumarins was also demonstrated. The presence of an OH group in position 7 of 3‐(1,2,4‐triazol‐3‐yl)coumarins opens up prospects for their use as building blocks, as it allows their modification both at the hydroxyl group by acylation and alkylation and at the benzene ring by aminomethylation.