Computational Comparisons of Pericyclic Reactions between Aminoborane (F3C)2BNMe2 and Substituted Butadienes: Dominance of the Diels–Alder [4 + 2] Cycloaddition

Abstract

Different reaction types known to occur when (F3C)2BNMe2, 1, acts as an inorganic alkene were studied computationally. Diels–Alder cycloadditions dominate three other pericyclic reaction types by exhibiting lower activation barriers and greater exothermicities. An upper bound of ΔG298‡ = 100 kJ mol–1 appears appropriate for defining reactions that will occur experimentally. Substituting hydrogens with π-donor groups on the butadiene leads to lowered barriers, such that the model predicts a number of plausible Diels–Alder reactions. Such substitution at the butadiene 2-posiiton is predicted to lead to exclusive formation of rings with the substituent on the carbon adjacent to the boron-bound carbon, a result caused by barrier differences traceable to electronic issues. The steric demand of the (F3C)2B moiety limits plausible reactivity to cases where at least one CH2 terminus is present on the butadiene. Thus, in reactions between 1 and a 1-substituted butadiene, the boron binds the CH2 terminus and the nitrogen binds the CH(R) terminus. Diels–Alder reactions between 1 and 1,4-disubstituted butadienes are predicted to be implausible regardless of the electronic properties of the substituents.