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

A 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.