A Computational Study of the Cycloaddition of Thiobenzophenone S-Methylide to Thiobenzophenone

Abstract

The cycloaddition of thiobenzophenone S-methylide to thiobenzophenone, an experimentally well-known reaction, was studied, using (U)HF/3-21G* for finding stationary points and (U)B3LYP/6-31G*//(U)HF/3-21G* single-point calculations for energies. Some optimizations were performed by (U)B3LYP/ 6-31G* to check the reliability of the calculations. The comparison of the concerted pathways and stepwise reactions via C,C-biradicals and C,S-zwitterions showed that the formation of a tetraphenyl-substituted C,C-biradical and its ring closure to 4,4,5,5-tetraphenyl-1,3-dithiolane constitutes the energetically most probable pathway of product formation, despite the fact that the regioisomeric 2,2,4,4-tetraphenyl-substituted product is more favorable by 17 kcal mol(-1). Model calculations on bond dissociation energies showed that (U)B3LYP with various basis sets overestimates radical stabilization, whereas CBS-QB3 closely reproduced experimental values. Results with the BLYP functional are similar to those with B3LYP. The consequences of the overestimation of radical stability for the cycloaddition mechanism involving biradicals are discussed. Thiobenzophenone S-methylide, if not captured by a dipolarophile, dimerizes to 2,2,3,3-tetraphenyl-1,4-dithiane. Calculation disclosed likewise a tetraphenyl-substituted C,C-biradical as intermediate.

The Effect of Pressure on Hydrogen Transfer Reactions with Quinones

“…Depending on the basis set, the values range from 16 to 34 %. As observed in other examples, [26] such low BRCs also yield closed-shell wave functions (S 2 = 0) when determined by unrestricted Figure 2. Volume profile [a] of the reaction between 1,4-cyclohexadiene (3) and DDQ (1 a).…”

Rolf Huisgen: Some Highlights of His Contributions to Organic Chemistry

“…7). A DFT study showed that this result is best explained by formation of a biradical intermediate, which closes to the 4,5-substituted 1,3-dithiolane [93]. A combined experimental and theoretical study on cycloadditions of aliphatic thiocarbonyl S-ylides to thiobenzophenone, where synchronous and two-step pathways compete, showed good agreement between experiment and theory [94].…”

[2 + 3]‐Cycloadditions of Phosphonodithioformate S‐Methanides with CS, NN, and CC Dipolarophiles

“…Whereas, in the case of 5a 4 in the absence of trapping agents yielded 9 as the sole product. This reaction corresponds with the formation of analogous products from thioketones and α-diazo carbonyl derivatives [8].…”

“…Among the few methods of their generation, the reaction of CH 2 N 2 with C=S dipolarophiles and subsequent elimination of N 2 is applied most frequently. The reactive 1,3-dipoles formed in situ can be trapped by different electron-deficient dipolarophiles, but aromatic thioketones proved to be the most reactive ones (superdipolarophiles [4]). Less reactive C=S dipolarophiles are non-enolizable aliphatic thioketones, 1,3-thiazole-5(4H)-thiones, dithioesters, and O-alkyl thioesters.…”