Physics

Dipole

Organic chemistry

Electric dipole transition

Catalysis

Computational chemistry

Bond dipole moment

Electric dipole moment

Magnetic dipole

Moment (physics)

Chemistry

Absolute configuration

Diels–Alder reaction

Classical mechanics

Journal of the American Chemical Society

The manuscript studies the enantioselectivity and stereoselectivity of Diels–Alder (DA) cycloadditions between cyclopentadiene (CPD) and a variety of dienophiles (ranging from halo-ethenes to cyano-ethenes), under oriented external electric fields (OEEFs). Applying OEEFs oriented in the X/Y directions, perpendicular to the reaction axis (Z), will achieve complete isomeric and enantiomeric discrimination of the products. Unlike the Z-OEEF, which involves charge-transfer from the diene to the dienophile, and thereby brings about catalysis due to increased intramolecular bonding, an OEEF along X, aligned parallel to the C1-C4 atoms of CPD, will lead to R/S enantiomeric discrimination by means of intramolecular-bond polarization. A Y field will discriminate endo/exo stereoisomers in a similar mechanism. The XY field-combination will resolve both R/S and endo/exo. The resolution is complete and can be achieved at will by flipping the direction of the field along the X and Y axes. The preconditions for achieving the enantiomeric and isomeric discrimination are discussed and require fixing of the CPD onto a surface. In so doing the chiral discrimination is achieved by dipole-moment selection rules, such that the field filters out one of the enantiomers, which is highly raised in energy by dipole selection. The dependence of the discrimination on the polarity of the dienophiles leads to a predictive trend.

Oriented-External Electric Fields Create Absolute Enantioselectivity in Diels–Alder Reactions: Importance of the Molecular Dipole Moment