PREPARATION OF URACIL BY CYCLOREVERSION - STRUCTURE OF CYCLOALKANE-FUSED, CYCLOALKENE-FUSED DIURACILS AND NORBORNANE-FUSED, NORBORNENE-FUSED DIHYDROURACILS

The reactions of the 2-amino-1-cycloalkane-, cycloalkene-, norbornane- and norbornenecarboxylates 1-9 with potassium cyanate gave urea esters, which were cyclized to cycloalkane-, cycloalkene-, norbornane- and norbornene-fused 5,6-dihydrouracils 10-17. On cyclization, the urea ester formed from trans-4-cyclohexene-1-carboxylate, furnished the cis-fused 5,6-dihydropyrimidine-2,4(1H,3H)-dione. On heating, the norbornene-diexo-fused dihydrouracil 16 yielded 2,4-pyrimidinedione through the splitting-off of cyclopentadiene. The structures of the compounds were proved by H-1 and C-13 nmr spectroscopy.