Competition between [2 + 1]- and [4 + 1]-cycloaddition mechanisms in reactions of conjugated nitroalkenes with dichlorocarbene in the light of a DFT computational study

Abstract

The competition between [2 + 1] and [4 + 1] channels regarding reactions of conjugated nitroalkenes with dichlorocarbene was explored based on B3LYP/6-31G(d) calculations. It was found that, in the case of cycloadditions involving parent nitroethene and its 1-substituted analogs, the [2 + 1] scheme should be treated as possible only from the kinetic process point of view. On the other hand, in similar reactions involving 2-substituted nitroethenes, both channels considered may compete. Additionally, mechanistic aspects of all cycloadditions were analyzed. It was found that the considered [2 + 1]-cycloadditions proceed via a non-polar mechanism with a biradicaloidal transition state (TS), whereas [4 + 1]-cycloadditions proceed via a polar mechanism with a zwitterionic TS.

Mechanistic aspects of the synthesis of seven‐membered internal nitronates via stepwise [4 + 3] cycloaddition involving conjugated nitroalkenes: Molecular Electron Density Theory computational study

“…Alternatively, some 5INs can be synthetized via the [4 + 1] cycloaddition reaction between some carbene systems and nitroethene analogues (Scheme 2). 7 …”

A DFT Study on the Molecular Mechanism of Additions of Electrophilic and Nucleophilic Carbenes to Non-Enolizable Cycloaliphatic Thioketones

“…For the simulation of the reactions paths, the wb97xd functional included in the GAUSSIAN 09 package [48] and the 6-311g(d,p) basis set [49,50] including both diffuse and polarization functions for all relevant atoms was used. A similar theory level has been commonly used for the mechanistic research aspects of cycloaddition reactions [28,39,[51][52][53][54][55]. All localised stationary points have been characterized using vibrational analysis.…”

“…Whereas theoretical studies on mechanisms of [2 + 1] cycloadditions of carbenes with ethylenic compounds are widely discussed in numerous publications [1][2][3][26][27][28], there is a lack of similar works focused on reactions with thiocarbonyl compounds. Appearance of 1,3-dipoles such as azomethine ylides, carbonyl ylides, or thiocarbonyl ylides as reactive intermediates in reactions of carbenes/carbenoiods with imines [29,30], carbonyl [31], and thiocarbonyl compounds [32,33], respectively, has been discussed in numerous publications but the details of postulated mechanisms have never been elucidated using theoretical methods.…”

“…Due to our continuous interest in the chemistry of thiocarbonyl compounds on one side and in nucleophilic as well as electrophilic carbenes on the other one, we decided to study reactions of some, synthetically significant thioketones with both types of carbenes in detail, and the DFT method was selected as an appropriate tool to solve this problem. Whereas theoretical studies on mechanisms of [2 + 1] cycloadditions of carbenes with ethylenic compounds are widely discussed in numerous publications [1][2][3][26][27][28], there is a lack of similar works focused on reactions with thiocarbonyl compounds. Appearance of 1,3-dipoles such as azomethine ylides, carbonyl ylides, or thiocarbonyl ylides as reactive intermediates in reactions of carbenes/carbenoiods with imines [29,30], carbonyl [31], and thiocarbonyl compounds [32,33], respectively, has been discussed in numerous publications but the details of postulated mechanisms have never been elucidated using theoretical methods.…”

Unveiling the high regioselectivity and stereoselectivity within the synthesis of spirooxindolenitropyrrolidine: A molecular electron density theory perspective

“…The reactions were also inferior in DMSO, DMF, THF and CCl 4 . [42] The B3LYP/6-31G(d) computational level has been applied to successfully understand the selectivity and mechanism of several recent 32CA reactions, [34,[43][44][45][46][47] which justifies its applicability in the present MEDT study.…”