Participation of Phosphorylated Analogues of Nitroethene in Diels–Alder Reactions with Anthracene: A Molecular Electron Density Theory Study and Mechanistic Aspect

Abstract

The structure and the contribution of the bis(2-chloroethyl) 2-nitro 1a and 2-bromo-2-nitroethenylphosphonates 1b with anthracene 2 in the Diels–Alder (DA) reactions have been studied within the Molecular Electron Density Theory (MEDT) at the B3LYP functional together with 6-31G(d), 6-31+G(d) and 6-31+G(d,p) basic sets. Analysis of the Conceptual Density Functional Theory (CDFT) reactivity indices indicates that 1a and 1b can be classified as a strong electrophile and marginal nucleophile, while 2 is classified as a strong electrophile and strong nucleophile. The studied DA reactions take place through a one-step mechanism. A Bonding Evolution Theory (BET) of the one path associated with the DA reaction of 1a with 2 indicates that it is associated with non-concerted two-stage one-step mechanism. BET analysis shows that the first C2-C3 single bond is formed in Phase VI, while the second C1-C6 single bond is formed in the Phase VIII. The formation of both single bonds occurs through the merging of two C2 and C3, C1 and C6 pseudoradical centers, respectively.