Understanding the uniqueness of the stepwise [4+1] cycloaddition reaction between conjugated nitroalkenes and electrophilic carbene systems with a molecular electron density theory perspective

摘要

The [4 + 1] cycloaddition (41CA) and [2 + 1] cycloaddition (21CA) reactions of the alpha-halogeno-nitroalkenes with carbene have been studied using the molecular electron density theory through density functional theory calculations at the MPWB1K(PCM)/6-311G(d,p) computational level. The 41CA reaction take place through a polar two-step mechanism involving the formation of a zwitterionic intermediate. The competitive 21CA reaction path proceeds according to nonconcerted two-stage one-step. Bonding evolution theory analysis of 41CA reaction allows the distinguishing of four groups along the reaction path. The reaction begins with rupture of the C-C double bond of the alkene moiety and formation of thepseudoradicalcenter. Formation of the O-C and C-C new single bonds begins in subsequent phases. In the last stage of the 41CA reaction path, we observed the formation of an N-C new double bond. In the case of 21CA reaction path, we observed the successive rupture of the C-C double bond of the alkene moiety, formation of C-C new single bond andpseudoradicalcenter, and creation of a second C-C single bond.