Synthesis of new imidazo[1,2-a]pyrazolo[4,3-e]pyrimidin-4(6H)-one derivatives by iodocyclization of 6-alkenyl(alkynyl)-aminopyrazolo[3,4-d]pyrimidin-4(5H)-ones

6-Allyl(diallyl, prop-2-yn-1-yl)amino-1-R-pyrazolo[3,4- d ]pyrimidin-4(5 H )-ones reacted with iodine to give angularly fused 8-iodomethyl-7,8-dihydro-1-R-imidazo[1,2- a ]pyrazolo[4,3- e ]pyrimidin-4(6 H )-ones which were treated with sodium acetate to obtain 8-methylidene-1-R-7,8-dihydroimidazo[1,2- a ]pyrazolo-[4,3- e ]pyrimidin-4(6 H )-ones as a result of elimination of hydrogen iodide. 8-Methylidene-1-R-7,8-dihydroimidazo[1,2- a ]pyrazolo[4,3- e ]pyrimidin-4(6 H )-ones were converted into 8-methyl-1-R-imidazo[1,2- a ]pyrazolo-[4,3- e ]pyrimidin-4(5 H )-ones on heating to the melting point. 8-Methylidene-1-phenyl-7,8-dihydroimidazo-[1,2- a ]pyrazolo[4,3- e ]pyrimidin-4(6 H )-one underwent isomerization into linearly fused 6-methyl-1-phenyl-1,8-dihydro-4 H -imidazo[1,2- a ]pyrazolo[3,4- d ]pyrimidin-4-one on heating in sulfuric acid.