A molecular electron density theory study of polar Diels-Alder reaction between 2,4–dimethyl–5–ethoxyoxazole and ethyl 4,4,4–trifluorocrotonate

Abstract

The mechanism and the selectivity of Diels-Alder (DA) reaction between 2,4–dimethyl–5–ethoxyoxazole (DE 4) and ethyl 4,4,4–trifluorocrotonate (ET 5) at 298 K in the presence of toluene have been theoretically reviewed by the molecular electron density theory (MEDT) with the computational level of MPWB1K/6–311G(d,p). In the DA reaction, the regioselectivity was studied at the reactive positions of the DE 4 and ET 5 through the studied nucleophilic and electrophilic Parr functions. The conceptual density functional theory (CDFT) reactivity indicated that ET 5 and DE 4 work as a strong electrophile and nucleophile, respectively. The energy profiles indicated that the transition state TS1n generates a unique product corresponding cycloadduct (CA) of CA1n, which is completely consistent with the experimental research. The endo stereoselectivity was confirmed by both results of molecular electrostatic potential (MEP) and the non-covalent interactions (NCIs) at the C1–C6 regioisomeric path. Electron localization function (ELF) and the intrinsic reaction coordinate (IRC) pathways were used to understand the mechanism of this DA reaction.