Criteria for the Elucidation of the Pseudopericyclic Character of the Cyclization of (Z)‐1,2,4,6‐Heptatetraene and Its Heterosubstituted Analogues: Magnetic Properties and Natural Bond Orbital Analysis

Abstract

The electrocyclization of heterosubstituted derivatives of (Z)-1,2,4,6-heptatetraene, (2Z)-2,4,5-hexatrien-1-imine and (2Z)-2,4,5-hexatrienal exhibit some features which suggest a pseudopericyclic mechanism. In order to examine this, a comprehensive study including the determination of magnetic properties to estimate aromaticity and an NBO analysis throughout the reaction path was conducted. The cyclization of 5oxo-2,4-pentadienal, a process of unequivocal pseudopericyclic nature, was studied for comparison. The results suggest that, although the lone electron pair on the heteroatom in the heptatetraene derivatives seemingly plays a crucial role in the reaction mechanism, it does not suffice to deprive the reaction from the essential features of a pericyclic disrotatory electrocyclization.

Fluorine effect on pericyclic and pseudopericyclic processes: Evidences and ab initio theory

“…Electrocyclic ring opening (ERO) of pyrone has been found to be pseudeopericyclic by Birney and coworkers 27 and later Rodríguez and coworkers 28 have confirmed this by using NBO analysis. We [29][30] have studied the thermolysis of 2-pyrone and 6-halo-2-pyrone and have found that fluorine substitution substantially altered the potential energy surface for ERO, sigmatropic rearrangement and electrocyclic ring closing (ERC) of pyrones.…”

“…This is in agreement with proposition that the involvement of LP of hetero atom may push the pericyclic reaction to become more pseudopericyclic. 28 …”

“…Later many methods based on the magnetic properties such as NICS, 7,8 ACID 9-12 have been developed to characterize pseudeopericyclic reactions. These methods were successfully used by Rodrίguez Otero and their coworkers, [13][14][15][16][17][18][19] to identify the nature of reactions as pericyclic or pseudopericyclic. Lopez and de Lera et al 20 showed that pseudopericyclic reactions do not show a maximum in ellipticity of the forming bond along the reaction coordinate.…”

A DFT Study of the Concerted Cyclisation of 3‐Azidopropenal to Isoxazole:Is it a Pseudopericyclic Reaction According to Its Magnetic Properties?

“…In previous papers we have demonstrated the necessity to study the whole process and not only the transition state in order to define a process conclusively as pericyclic or pseudopericyclic. [2][3][4][5] In addition, we have emphasised the importance of studying the magnetic properties along the reaction profile in this controversial matter. [5] Figure 1.…”

“…For this reason, this work reports a comprehensive study of the magnetic properties along the reaction profile of the whole cyclisation of 3-azidopropenal. [2][3][4] The aromaticity was examined in terms of magnetic susceptibility (χ), magnetic susceptibility anisotropy (χ anis ) and the nucleus-independent chemical shifts (NICS) reported by Schleyer. [25] Birney [15] found that disconnections can also occur in coarctate reactions, similarly to pseudopericyclic reactions.…”