On the reactions of 6-phosphoranylideneaminouracils and related 6-aminouracils with 2,4,6-cyclooctatrienone: Reactions of the intermediates of uracil-annulated 8-azabicyclo[5.3.1]undecatetraene ring systems

The reaction of 1,3-dimethyl-6-phosphoranylideneaminouracil (4) with 2,4,6-cyclooctatrienone (7) in AcOH gives an intermediacy of uracil-annulated 8-azabicyclo[5.3 1]undeca-2,4,7,9-tetraene (9), which results in the formation of 9-acetoxy-5a,10-methano-2,4-dimethyl-2H-5,5a,6,8a,9,10-hexahydrocyclopent[b]-pyrimido[5,4-f]azepine-1,3(4H)-dione and 1,3,7- and 1,3,5-trimethylpyrido[2,3-d]pyrimidine-2(1H),4(3H)-diones (12 and 13) after several reaction sequences. A similar reaction using 6-amino-1,3-dimethyluracil (5) also afforded the same products probably via uracil-annulated 8-azabicyclo[5.3.1]undeca-2,4,6,9-tetraene (14). A similar intermediate is also postulated in the reaction of 3-methyl-6-methylaminouracil (6) with 2,4,6-cyclooctatrienone, and results in the formation of 9-acetoxy-5a,10-methano-2,4,5-trimethyl-2H-5,5a,6,8a,9,10-hexahydrocyclopent-[b]pyrimido[5,4-f]azepine-1,3(4H)-dione (26), 3,7,8- and 3,5,8-trimethylpyrido-[2,3-d]pyrimidine-2(3H),4(8H)-diones (27 and 28).