Substituted 2-borabicyclo(1.1.0)but-1(3)-enes (2BB’s) are a kind of novel molecules with inverted carbon–carbon bonds whose orders range between one and two. Considering the significant interest in the Diels–Alder (D–A) reactions of substituted cyclopropenes, here we studied the bonding and D–A reactions of 24 substituted 2BB molecules at the B3LYP-D3/6-311G** theoretical level. Computations showed that the inverted C=C bond lengths fall in the range of 1.46–1.50 A and 2BB is of significant characteristic of a singlet biradical with two σ single electrons and π aromatic conjugation over the three-membered rings. Yet ab initio valence bond computations showed that the inverted bonds are charge-shifted, and the ionic resonance structures arising from charge-shifting are of carbene characteristics as well. Thus, substituted 2BB’s can also be considered as B-heterocyclic carbenes. Since the LUMOs of the 2BB derivatives are similar to those of ethene and cyclopropene, we studied their D–A reactions with butadiene. All cycloaddition reactions kinetically and thermodynamically favor the formation of the derivatives of 7-bora-oct-3-ene[4.1.1]propellane undergoing endo transition states. Notably, there is a good correlation between the reaction barriers and the hyperconjugative aromatic and antiaromatic stabilization enthalpies for all substituted 2BB’s. In other words, the differences in their reactivity result from the difference in their aromatic stability.