Addition of substituted (alkoxy)allyllithium and zinc reagents to cyclopropenone acetal takes place smoothly to give carbometalation products of well-defined regio- and stereochemistry. The pathways of product formation depends on the metal. The (alkoxy)allylzinc reagents add to the cyclopropene in such a manner that the alpha-carbon attached to the alkoxy group becomes bound to the olefin. The regioselectivity of the (alkoxy)-allylzincation is independent of the allyl substituents, the diastereoselectivity for the newly formed carbon-carbon bond is excellent (> 97%), and the geometry of the olefinic bond in the product was always exclusively cis (if applicable). On the other hand, the regioselectivity of the (alkoxy)-allyllithiation is dependent on the substituent, while the diastereoselectivity remains constantly high (>97%). Theoretical studies supported this conjecture by revealing that a(hydroxy)allyllithium species of pi-allylmetal nature can react with cyclopropene via two [2 + 2]-type four-centered transition states of similar energies leading alpha- and gamma-adducts, while the zinc species of sigma-allylmetal nature reacts via a single [2 + 4]-type six-centered transition state leading to an alpha-adduct.