Synthesis of (3,6-dihydro-2H-pyran-2-yl)phosphonate derivatives and investigation of catalyst effect on frontier molecular orbitals using DFT method

GRAPHICAL ABSTRACT

ABSTRACT

Hetero Diels-Alder (HDA) reactions between 2,3-dimethyl-1,3-butadiene and diethyl ester of aroyl phosphonates catalyzed by AlCl₃ to afford (3,6-dihydro-2H-pyran-2-yl) phosphonate derivatives were investigated. Aroyl phosphonates with electron-withdrawing groups generally resulted in better isolated chemical yields. A stoichiometric amount of AlCl₃ rather than a catalytic amount was necessary to activate the cycloaddition reaction. The amount of AlCl₃ catalyst and its effect on LUMO of ethyl ester benzoyl phosphonate were also investigated by performing density functional theory (DFT) (B97D/6-31+G(d,p)) computations in dichloromethane. An increased loading of AlCl₃ induced a considerable decrease in the LUMO energy of ethyl ester of benzoyl phosphonate. The computed Gibbs free activation energy is 17.03 kcal/mol in DCM at 0°C using the same computational level.

KEYWORDS:

• Aroyl phosphonate
• cycloaddition reaction
• 2,3-dimethyl 1,3-butadiene
• B97D
• frontier molecular orbital

Acknowledgments

We thank TUBITAK ULAKBIM, High Performance and Grid Computing Center (TR-Grid e-Infrastructure) for the computations.

Funding

Financial support from the Scientific and Technological Research Council of Turkey (TUBITAK) and the Middle East Technical University (METU) are all appreciatively acknowledged.