The reaction of ground state boron atoms, 11B(2Pj), with allene, H2CCCH2(X1A1), was studied under single collision conditions at a collision energy of 21.5 kJ mol(-1) utilizing the crossed molecular beam technique; the experimental data were combined with electronic structure calculations on the 11BC3H4 potential energy surface. The chemical dynamics were found to be indirect and initiated by an addition of the boron atom to the pi-electron density of the allene molecule leading ultimately to a cyclic reaction intermediate. The latter underwent ring-opening to yield an acyclic intermediate H2CCBCH2. As derived from the center-of-mass functions, this structure was long-lived with respect to its rotational period and decomposed via an atomic hydrogen loss through a tight exit transition state to form the closed shell, C2v symmetric H-C is equivalent C-B=CH2 molecule. A brief comparison of the product isomers formed in the reaction of boron atoms with methylacetylene is also presented.