Abstract
Photoreaction of diketene with 6-methyluracil gives rel-(1R, 6R, 8S)-1-methyl-3, 5-dioxo-2, 4-diazabicyclo [4. 2. 0] octane-8-spiro-2'-(oxetan)-4'-one (10a), rel-(1R, 6R, 8R)-1-methyl-3, 5-dioxo-2, 4-diazabicyclo [4. 2. 0] octane-8-spiro-2'-(oxetan)-4'-one (10b), rel-(1R, 6R, 7S)-1-methyl-3, 5-dioxo-2, 4-diazabicyclo [4. 2. 0] octane-7-spiro-2'-(oxetan)-4'-one (10c), and rel-(1R, 6R, 7R)-1-methyl-3, 5-dioxo-2, 4-diazabicyclo [4. 2. 0] octane-7-spiro-2'-(oxetan)-4'-one (10d). Heating of compounds 10a and 10b at their decomposition points results in decarboxylation to give rel-(1R, 6R)-1-methyl-8-methylene-3, 5-dioxo-2, 4-diazabicyclo [4. 2. 0] octane (11). Similarly, thermolysis of 10c and 10d affords rel-(1R, 6S)-1-methyl-7-methylene-3, 5-dioxo-2, 4-diazabicyclo [4. 2. 0] octane (12). Surtcture assignments of 10b and 10c by X-ray crystallographic analysis are described. The structures were solved by the direct method and refined to R values of 4.81% for 10b and 6.79% for 10c.
