Structures of alchomeine, imidazo-(1-2h) pyrimidine derivative, of isoalchomeine, imidazo-(1-2a)-imidazole derivative, and of alchomeinone have been determined by physical methods and chemical correlations. Synthesis of isopropyl-4 imidazolidone-2 (S) leads to the determination of the absolute configurations of these products.