A DFT investigation of the addition reaction of monomeric lithium enolate derived from propiophenone to propene oxide: Examination of the possible transition structures

The addition reaction of monomeric lithium enolate (Z)-1, derived from propiophenone, to propene oxide 2, was examined to clarify the exact geometry of the transition state (TS) involved in this type of reaction. The eight possible TSs and the corresponding pathways, four leading to syn gamma-hydroxy ketone (gamma-HK) 3 and four leading to anti gamma-HK 4, were compared, using the B3LYP/631+G(d)//B3LYP/6-31+G(d) theory level in vacuo and in the presence of the reaction solvent (toluene/hexane). In every case, the favored pathway involves a TS where the enolate C=C and the epoxide C-C are in a gauche relationship and where the Li+ is stabilized by some C-C and C-H sigma bonds of epoxide 2.