Understanding the Influence of the Trifluoromethyl Group on the Selectivities of the [3+2] Cycloadditions of ThiocarbonylS‐methanides with α,β‐Unsaturated Ketones. A MEDT study

Abstract

Experimentally (G. Mlostoń et al., J. Fluor. Chem. 2016, 190, 56–60), it has been found that the type of the obtained cycloadduct of the [3+2] cycloaddition (32CA) reaction of thiocarbonyl S‐methanides with α,β‐unsaturated ketones depends strongly on the location of the trifluoromethyl group. In the case of enones containing the CF3CH=CH moiety, the 32CA reaction occurs chemo‐ and regioselectively onto the C=C double bond giving trifluoromethylated tetrahydrothiophene derivatives. On the other hand, enones containing the CF3−C=O fragment react as carbonyl heteroethylenes leading to trifluoromethylated 1,3‐oxathiolanes also in a chemo‐ and regioselective manner. Our aim in the present work is to perform a theoretical study of the all chemo‐, regio‐, and stereo‐isomeric reaction paths of these 32CA reactions within the Molecular Electron Density Theory. Activation Gibbs free energies, calculated at the B3LYP/6‐311G(d,p) level in tetrahydrofurane at −40 °C, show that the ortho/endo reaction path giving the trifluoromethylated tetrahydrothiophene is more favoured, while the meta/endo reaction path leading to trifluoromethylated 1,3‐oxathiolanes is more preferred in total agreement with experimental findings. The low activation barriers in combination of the Electron Localization Function topological analysis of the most relevant points along the Intrinsic Reaction Coordinate reveals the pseudomonoradical character of the studied 32CA reactions.

A Mechanism Study and an Investigation of the Reason for the Stereoselectivity in the [4+2] Cycloaddition Reaction between Cyclopentadiene and Gem-substituted Ethylene Electrophiles

“…Today, in addition to conjugated 1,3-dienes, conjugated nitroalkenes [5][6][7] are tried quite often as hetero-analogues of dienes. The use of ethene heteroanalogues as components of the cycloaddition reaction includes molecular segments containing nitrogen [8,9], oxygen [10,11], sulphur [12,13], selenium [14].…”