5‐Aza‐adenine Derivatives for Crop‐Protection: Multicomponent Synthesis, Experimental and Theoretical Structural Analysis

Abstract

AbstractA microwave‐assisted synthesis of 7‐amino‐1,2,4‐triazolo[1,5‐a][1,3,5]triazine‐2‐propanamides was developed using a three‐component, catalyst‐free reaction of cyanamide and trimethyl orthoformate with 3‐(5‐amino‐1H‐1,2,4‐triazol‐3‐yl)propanamides (3). The reaction tolerated structurally diverse substrates and proceeded chemo‐ and regio‐selectively, affording the target compounds in high purity in 5–10 minutes. The convenient chromatography‐free isolation and purification of the products add practicality to this method. The structural features of the prepared compounds were investigated using dynamic NMR spectroscopy, X‐ray crystallography and computational chemistry calculations. X‐ray crystallography performed on a representative compound, 3‐(7‐amino‐1,2,4‐triazolo[1,5‐a][1,3,5]triazin‐2‐yl)‐N‐(4‐benzyl)propanamide (4 l), showed the overall molecular conformation to adopt the shape of the letter C. Notable localisation of π‐electron density is found within the 1,2,4‐triazolo[1,5‐a][1,3,5]triazine system; a relatively short C−NH2 bond is consistent with restricted rotation about this bond. This study also presents a detailed analysis of the molecular interactions in 4 l using DFT and QTAIM methods with a focus on the hydrogen‐bonding and π‐stacking interactions that influence the molecular packing of 4 l. The findings reveal the significant roles of N−H⋅O, N−H⋅N and C−H⋅N interactions, along with electrostatically enhanced π⋅π contacts. A broad screening for insecticidal, fungicidal and herbicidal properties identified several compounds with potent herbicidal activity against Matricaria inodora.