Formylation of 4,7‐Dihydro‐1,2,4‐triazolo[1,5‐a]pyrimidines Using Vilsmeier–Haack Conditions

Abstract

Formylation of 5‐methyl‐7‐phenyl‐4,7‐dihydro‐1,2,4‐triazolo[1,5‐a]pyrimidine 1a using Vilsmeier–Haack conditions yields 5‐methyl‐7‐phenyl‐4,7‐dihydro‐1,2,4‐triazolo[1,5‐a]pyrimidin‐6‐ylcarbaldehyde 3a. 5,7‐Diaryl‐4,7‐dihydro‐1,2,4‐triazolo[1,5‐a]pyrimidines 1b, 1c in this reaction apart from formylation undergo recyclization into 5‐aryl‐1,2,4‐triazolo[1,5‐a]pyrimidin‐6‐ylmethane derivatives 4b, 4c, 5b, 5c, and 6. The structure of the synthesized compounds was determined on the basis of NMR, IR, and MS spectroscopic data and confirmed by the X‐ray analysis of the 6‐(ethoxy‐phenyl‐methyl)‐5‐phenyl‐[1,2,4]triazolo[1,5‐a]pyrimidine 6, 5‐phenyl‐6‐(1‐phenyl‐vinyl)‐[1,2,4]triazolo[1,5‐a]pyrimidine 11, and 7‐phenyl‐6‐(1‐phenyl‐vinyl)‐[1,2,4]triazolo[4,3‐a]pyrimidine 12.