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The optically active cyclopropanecarbonyl azide 6 (ee 90%) was synthesized from the known cyclopropanecarboxylate 4. Upon heating in refluxing benzene, 6 rearranged to the dihydroazepinone 9 (ee 65%) via the isocyanate 7 and the enamide 8. In contrast, the dimethyl‐substituted cyclopropanecarbonyl azide 20 rearranged to the isocyanate 21, but decomposed at higher temperatures rather than to undergo Cope rearrangement to 22. The results are consistent with a mechanism involving a boat‐like endo‐transition state 11 for the rearrangement, which may not be reached with the dimethyl derivative 21 for steric reasons. The origin of change in enantiomer composition, upon going from 6 to 9, is at present unknown.

The cyclopropenation of diethoxypropyne (1) with methyl diazoacetate in the presence of [Rh₂{(2S)‐mepy}₄] (mepy=methyl 5‐oxopyrrolidine‐2‐carboxylate) proceeds with >95% ee. The resulting cyclopropenecarboxylate 2 underwent stereoselective hydrogenation to the cis‐cyclopropane 3. Hydrolysis of the acetal function of 3 liberated the formyl cyclopropenecarboxylate 4, which was transformed by Wittig reaction with the phosphonate 5 to afford dehydroamino acid 6 as a mixture of (Z)‐ and (E)‐isomers in various proportions. The (Z)‐isomer 6a was hydrolyzed, and the structure and the absolute configuration of the (Z)‐dicarboxylic acid 7a were established by X‐ray crystallography. The cis‐divinylcyclopropane 11 (ee>95%), in turn, was synthesized from 4 via Wittig reaction to afford 8, which was transformed to the aldehyde 10 and subjected to a second Wittig reaction. Thermolysis of 11 afforded (+)‐dictyopterene C′ (12) in quantitative yield.