SYNTHESIS AND PROPERTIES OF 2,4,6-TRIMETHYLENETRICYCLO[3.3.0.0(3,7)]OCTANE (STELLATRIENE) AND ITS ALKYL DERIVATIVES - CANDIDATES FOR A 2-STEP COPE REARRANGEMENT

The synthesis of 2,4,6-trimethylenetricyclo[3.3.0.0(3,7)] octane (stel latriene, 9), its hexamethyl derivative 37, and the spirocyclic deriva tives 67 and 68, substituted at the carbon atom of the saturated bridg e of the tricyclic system, are described. Key steps in the syntheses i nclude an intramolecular Paterno-Buchi reaction leading to tetracyclic oxetanes (e.g., 22b, 39, 47, 59, and 60) as well as the cleavage of t he oxetane ring induced by various bases. During the synthesis several dienones were prepared (35, 41, 50, 63, and 64). The trienes and the dienones rearrange to triquinane derivatives at temperatures between 2 5 and 50 degrees C. The half-lives of the molecules in solution have b een determined, which indicate only a moderate effect of the methyl gr oups on the stability. The rearranged products can best be explained b y assuming a stepwise Cope rearrangement via two allylic fragments.