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.
Highlights
Accepted: 11 September 2021Carbenes form a group of reactive intermediates in which the central the two-valent carbon atom plays the most important role, determining their structure and chemical behavior [1,2,3,4]
The global reactivity indices of the reactants, namely electronic potential μ, chemical hardness η, global electrophilicity ω, and global nucleophilicity N, were estimated in pursuance of the equations defined on the basis of conceptual density functional theory (CDFT) according to the equations recommended by Parr [35] and Domingo [34,45]
The presented computational study demonstrated that additions of dihalocarbenes to non-enolisable, cycloaliphatic thioketones proceed differently and depend on the type of carbene species involved in the reaction
Summary
Carbenes form a group of reactive intermediates in which the central the two-valent carbon atom plays the most important role, determining their structure and chemical behavior [1,2,3,4]. Tive intermediates in reactions of carbenes/carbenoiods with imines [29,30], carbonyl [31], Results and Discussion and thiocarbonyl2.compounds [32,33], respectively, has been discussed in numerous pubTheofpresented study is divided have into three firstly, theusing analysis lications but the details postulated mechanisms neverparts: been (i) elucidated the-of the electronic properties of addends and their intermolecular interactions according to oretical methods. Due to our continuous interest in the chemistry of thiocarbonyl comConceptual Density Functional Theory (CDFT) reactivity indices is carried out; (ii) in the pounds on one side and in nucleophilic as well as electrophilic carbenes on the other one, paragraph, a full mechanistic consideration of the reaction of dichlorocarbene (1a) we decided to study reactions of some, synthetically significant with both and with 2,2,4,4-tetramethylcyclobutane-1,3-dithione (2a) isthioketones explored, characterized, types of carbenesdiscussed; in detail,(iii) and the selected. Indices of Reagentsin the course of reactions of non-enolizable, sterically crowded thioketones
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