New Synthesis of N-Monosubstituted Propane-1,3-diamines

A new method has been proposed for the synthesis of N-monosubstituted 1,3-diamines through the protection of propane-1,3-diamine with phthalic anhydride in one step to produce 3,4-dihydropyrimido[2,1-a]­isoindol-6(2H)-one which is selectively alkylated at the imine nitrogen atom, followed by hydrolytic removal of the phthalyl protecting group. The target N-monosubstituted propane-1,3-diamines are thus obtained in up to 66% yield without formation of polyalkyl derivatives. A number of new compounds have been characterized; in particular, 1-methyl-6-oxo-2,3,4,6-tetrahydropyrimido[2,1-a]izoindol-1-ium iodide and its partial hydrolysis product, 3-(1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)-N-methylpropan-1-aminium iodide, have been studied by X-ray analysis.