| Popis: |
The synthesis of 2,4,6-trimethylenetricyclo[3.3.0.0 3,7 ]octane (stellatriene, 9), its hexamethyl derivative 37, and the spirocyclic derivatives 67 and 68, substituted at the carbon atom of the saturated bridge of the tricyclic system, are described. Key steps in the syntheses include an intramolecular Paterno- Buchi reaction leading to tetracyclic oxetanes (e.g., 22b, 39, 47, 59, and 60) as well as the cleavage of the oxetane ring induced by various bases. During the synthesis several dienones were prepared (3d, 41, 50, 63, and 64). The trienes and the dienones rearrange to triquinane derivatives at temperatures between 25 and 50°C. The half-lives of the molecules in solution have been determined, which indicate only a moderate effect of the methyl groups on the stability. The rearranged products can best be explained by assuming a stepwise Cope rearrangement via two allylic fragments |
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