uracil (2) readily undergoes thermal rearrangement at 130°to give mixtures of l,3,6-trimethylfuro[3,2-d] pyrimidine-2,4-dione (3) and l ,3-dimethyl-67f-pyrano [3,2-d] pyrimidine-2,4-dione (4). The course of the rearrangement is markedly dependent on solvent and can be directed to give mostly 3 (in DMF), equal amounts of 3 and 4 (in DMSO), or predominantly 4 (in xylene). With prolonged reaction times in xylene, compound 4 dimerizes to give a Diels-Alder adduct (5). The observed incorporation of deuterium from labeled 2 into 3 and 4 is consistent with a mechanism involving Claisen-type rearrangement of 2 to give 6allenyl-1,3-dimethyl-5-hydroxyuracil (8), which then rearranges to give either 3 or 4. An independent synthesis of 8 by photolysis of 4 in chloroform is described, and it is further shown that 8 reverts to 4 at 35°and rearranges to 3 under ionizing conditions. Photolysis of 4 in ethanol affords 3 directly. The 2-propynyl ether of 5-hydroxyuridine rearranges in boiling water to give the corresponding furo [3,2-d] pyrimidine nucleoside (10). In refluxing toluene, tri-0-acetyl-5-(2-propynyloxy)uridine affords the pyrano [3,2-d]pyrimidine nucleoside (11).
Summary3 H-Sch 58235 was prepared at a specific activity of 29.1 Ci/mmol by Ir(COD)(Cy 3 P)PyPF 6 catalysed exchange with tritium gas.14 C-Sch 58235 was prepared in three steps from p-hydroxy[ring-U-14 C]benzaldehyde with an overall radiochemical yield of 21%. 13 C 6 -Sch 58235 was similarly prepared in three steps from p-hydroxy[ring-U-13 C 6 ]benzaldehyde in an overall yield of 41%.
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