SATURATED HETEROCYCLES .248. SYNTHESIS OF 2,4-DIOXO AND 4-OXO-2-THIOXO DERIVATIVES OF OCTAHYDROCYCLOPENTA[D]PYRIMIDINES

Unsubstituted and l-benzyl-substituted cis-cyclopenta[d]pyrimidine-2,4 -diones and cis-2-thioxocyclopenta[d]pyrimidin-4-ones 9a,b and 10a,b w ere prepared from the corresponding cis-2-amino-1-cyclopentanecarboxyl ates 3 and 5 with potassium cyanate and thiocyanate. It was found that the cis derivatives 7a-h readily underwent ring closure, resulting in 3-substituted cis-2,4-cyclopenta[d]pyrimidinediones and cis-2-thioxoc yclopenta[d]pyrimidin-4-ones 11a-d and 12a-d, whereas the trans counte rparts 8a-d failed to cyclize, but gave hydrolysed amino acid derivati ves 13a,b and 14. This difference in the reactivities of the cis and t r-ans isomers is a further example of the difficulty of preparing cycl opentane trans-fused six-membered 1,3-heterocycles by ring closure.