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ChemInform Abstract The cyclopropanation of the unsymmetrically substituted allenes (Ia), (Ib) and (V) is accomplished by the decomposition of diazomethane (II) in the presence of Pd(II) compounds to yield the methylenecyclopropanes (IIIa), (IIIb) or (VI), which result by cyclopropanation of the less substituted carbon-carbon double bond of the starting allenes. Prolonged treatment of (IIIa) with (II) according to method A) affords the spirobicyclopentane (IV) in high yield, whereas the analogous treatment of (IIIb) or (VI) remains uneventful. Treatment of the cyclic allene (VII) with (II) gives the methylenecyclopropane (VIII). Prolonged treatment of this compound with (II) affords the corresponding dicyclopropane, but the yield is low.

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