Allenes frontier orbitals

The regiochemistry of the cycloadditions of allenes is not easily explained by these frontier orbitals. Penta-2,3-diene and acrylonitrile give the adducts Z- and -6.404 in which the central carbon of the allene, with the smaller HOMO coefficient, has bonded to the / carbon of the Z-substituted alkene.894 Equally unexplained is the regiochemistry of the reaction between allene itself and diazomethane, which gives more of the adduct 6.405 than of its regioisomer 6.406.893... 

Energetically this reaction can be expected to be dipole-HO-controlled ( Lumo - Fhomo = 15.5 eV), but this should have little regiocontrol since the LUMO of the allene is so little polarised. The LUMO(dipole)/ HOMO ene) interaction ( lumo - homo = 16.75 eV) might come into play, since the allene HOMO is polarised, but the orbitals do not match up to explain the high level of regioselectivity, since the larger coefficient in the LUMO of diazomethane is on carbon. Finally, the hydroboration of allenes gives mainly the product with the boron on the central carbon 6.407.895 With boron as the electrophilic atom, frontier... 

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