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

Abstract

The molecular mechanisms of addition of dihalocarbenes and dimethoxycarbene to thioketones derived from 2,2,4,4-tetrmethylcyclobutane-1,3-dione were examined on the basis of the DFT wb97xd/6-311g(d,p)(PCM) calculations. Obtained results demonstrated that the examined processes exhibit polar nature and in the case of electrophilic dichloro-, and dibromocarbenes are initiated by the attack of carbene species onto the sulfur atom of the C=S group. Remarkably, reactions involving more electrophilic carbenes (dichloro-, and dibromocarbene) proceeds via stepwise mechanism involving thiocarbonyl ylide as a transient intermediate. In contrast, analogous reactions with nucleophilic dimethoxycarbene occur via a single step reaction, which can be considered as the [2 + 1] cycloaddition reaction initiated by the attack onto the C=S bond. A computational study showed that difluorocarbene tends to react as a nucleophilic species and resembles rather dimethoxycarbene and not typical dihalocarbene species. Significantly higher reactivity of the thioketone unit in comparison to the ketone group, both present in 3-thioxo-2,2,4,4-tetramthylcyclobutanone molecule, was rationalized in the light of DFT computational study.

On the Question of the Formation of Nitro-Functionalized 2,4-Pyrazole Analogs on the Basis of Nitrylimine Molecular Systems and 3,3,3-Trichloro-1-Nitroprop-1-Ene

“…Analogously, equal results could be observed for the other reagent systems, as, in all cases, nitrylimine ( 2b – c ) was characterized by a higher value of the electronic chemical potential than nitroalkene ( 1 ). To sum up, all presented cycloaddition reactions should be classified as forward electron density fluxes (FEDF) in agreement with the CDFT analysis [ 45 , 46 , 47 , 48 ].…”

“…DFT calculations were performed using the WB97XD/6-311G(d,p) [74,75] level of theory. A similar computational level has already been successfully used for the exploration of mechanistic aspects of other cycloaddition processes [45][46][47]76]. Calculations of all critical structures were performed at temperature T = 298 K and pressure p = 1 atm.…”

Synthesis of Fluorinated and Fluoroalkylated Heterocycles Containing at Least One Sulfur Atom via Cycloaddition Reactions

“…Thiocarbonyl compounds are also perfect trapping reagents for carbenes in [2+1]-cycloadditions leading to fluorinated thiiranes or their desulfurized derivatives [ 4 ]. Remarkably, difluorocarbene reacts with the C=S bond via carbophilic attack, and in these reactions, it resembles the nucleophilic dimethoxycarbene [ 89 ] and not the electrophilic dichloro- or dibromocarbene [ 90 ].…”

On the Mechanism of the Synthesis of Nitrofunctionalised Δ2-Pyrazolines via [3+2] Cycloaddition Reactions between α-EWG-Activated Nitroethenes and Nitrylimine TAC Systems

“…Consequently, C-phenyl-N-(4-nitrophenyl)-nitrylimine (1c) and C-(4-nitrophenyl)-N-phenylnitrylimine (1e) can be classified both as a strong electrophiles and strong nucleophiles. Simultaneously, these nitrylimines will behave as ambiphilic species [38,39].…”