1,3-Dihydro-2H-imidazo[4,5-c]pyridin-2-one

Article abstract of DOI:10.1002/jhet.5570430341

A facile acid catalysed cyclisation method for the preparation of the cyclic urea 2H-imidazo[4,5-c]pyridin-2-one (2) in > 95% yield is reported. The biologically active compound 2 can be obtained by heating (3-amino-4-pyridinyl)-carbamic acid methyl, ethyl or tert-butyl esters (1a-c) in sulfuric acid (0.1%) or in aqueous HBF₄ (3.5 equivalents) for 10 min. - 3 hrs at 90 °C. The corresponding microwave-promoted (MW) reactions afforded the pure product 2 within few minutes. The 6-butylamino-substituted analogue (2a) was correspondingly obtained by MW irradiation in 99% yield by cyclisation of 2-(butylamino)-5-amino-4-pyridylcarbamic acid isopropyl ester (1d). Quantitative precipitation of product 2 was obtained by pH adjustment. The process represents a solvent-free, "green" method for the preparation of 2.