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Unsaturated bicyclic endoperoxides are efficiently cyclopropanated with excess diazomethane in the presence of catalytic Pd(OAc)2 in a stereoselective manner. This method represents a new peroxide preserving transformation. Whereas the unsaturated endoperoxides in the [2.2.1] series are attacked by the carbene from the exo face, the analogs with larger bridges are preferentially attacked from the face syn to the peroxo bridge. Only in the case of the benzannelated [2.2.2] system the attack occurs exclusively from the face proximal to the benzene ring. Certain strained cyclopropanated endoperoxides are reduced by diazomethane to give cis-diols. 1-Methylfuran endoperoxide gives rise to cis-1-formyl-2-acetylcyclopropane in excellent yield.

An unusual peroxide base promoted isomerization was uncovered. Saturated endoperoxides derived from fulvenes give rise to 2-vinyl-2-cyclopentenones upon treatment with DBU in CH(2)Cl(2) in a one-pot reaction. This methodology was applied to a convenient synthesis of dihydrojasmone. Moreover, functional groups placed on the side chain at C-6 participate in the base catalyzed isomerizations via conjugate attack at the enone moiety to give 2-cyclopentenones carrying oxygen heterocycles at C2.

An asymmetric synthesis of the spermidine alkaloid (-)-(2R)-dihydromyricoidine (5) was performed by employing two ring-enlargement reactions. The chiral center was introduced by a diastereoselective Michael addition of perhydropyridazine (7) to the a$-unsaturated ester 6. The (Z)-C=C bond was obtained by a selective Wittig reaction. The synthetic compound 5 was found to have a negative value for the specific rotation. This is in contrast to that of the natural product reported in the literature. Therefore, as an outcome of this synthesis, the absolute configuration of the natural alkaloid should be inverted to be as shown in structure V.

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