A DFT computational study on the molecular mechanism of reaction between pyridinium salts and π-deficient ethylenes: Why furan derivatives are formed instead of feasible cyclopropane derivatives and [3+2] cycloadducts?

Publication date: 15 August 2017 Source:Computational and Theoretical Chemistry, Volume 1114 Author(s): Saeedreza Emamian, Radomir Jasiński The reaction between 1-(2-amino-2-oxoethyl)pyridinium ylide 4 (PY4) and 1-methylene-3,4-dihydronaphthalen-2(1H)-one 5 (MDN5) in the presence of acetonitrile (CH3CN) was theoretically studied at the M06-2X/6-31G(d,p) computational level. Calculated relative Gibbs free energies indicate that encounters between PY4 and MDN5 in the reaction mixture result in the formation of the highly zwitterionic betaine-like intermediate IM1ca in an entirely C1C5 regio- and a cisoid-anti stereoselective manner over the course of a Michael addition reaction through a very low barrier (4.2kcal/mol) and a highly exergonic (24.7kcal/mol) pathway. While C1C5 regioselectivity can be rationalized via the analysis of the computed nucleophilic and electrophilic Parr functions at the reactive sites of reagents, the cisoid-anti stereoselectivity predominance over the cisoid-syn one can nicely be portrayed within the non-covalent interactions (NCIs) analysis at the cisoid-anti transition state TS1ca and cisoid-syn transition state TS1cs involved in the Michael addition reaction. The electron-localization function (ELF) quantum topological analysis obviously demonstrates that the C1 carbon atom in PY4 exhibits a pseudoradical character indicating the high reactivity of PY4 toward C5 electrophilic attack of MDN5 which is characterized with a very low barrier associ...

Source: Computational and Theoretical Chemistry - May 27, 2017 Category: Chemistry Source Type: research