Regioselectivity, stereoselectivity, and molecular mechanism of [3 + 2] cycloaddition reactions between 2-methyl-1-nitroprop-1-ene and (Z)-C-aryl-N-phenylnitrones: a DFT computational study.

Reaction paths for [3 + 2] cycloaddition (32CA) between 2-methyl-1-nitroprop-1-ene and (Z)-C-aryl-N-phenylnitrones were explored in detail at the B3LYP/6-31G(d) level of theory. All of the 32CA processes considered were found to be initiated by the attack of the most nucleophilic oxygen atom in the nitrone molecule on the most electrophilic carbon atom (Cβ) in the nitroethylene moiety. This type of interaction favors the formation of 4-nitro-substituted cycloadducts. Additionally, based on a molecular electron density theory (MEDT) study, the 32CA processes of interest should be considered polar processes with asynchronous transition states (TSs). However, the asynchronicity of the localized TSs is unexpectedly low and clearly insufficient to enforce a stepwise zwitterionic mechanism.