Effect of oriented external electric fields on the Staudinger [2 + 2] cycloaddition reaction: a computational study

The Staudinger ketene-imine [2 + 2] cycloaddition provides an efficient strategy to produce polysubstituted β-lactam rings, resulting in two pairs of enantiomers with cis/trans configurations. This reaction is also biomedically relevant as it provides access to carbapenem antibiotics. Given the importance of controlling the diastereoselectivity and enantioselectivity of this transformation, our computational efforts focused on investigating the effect of oriented external electric fields (OEEFs) on the Staudinger reaction between tert-butylcyanoketene and benzylideneaniline. We initially studied the theoretical mechanism for this reaction in the absence of electric fields in gas-phase condition. Then, we performed in-silico studies to evaluate the effect of electric fields on the outcome of the Staudinger reaction. Our results indicated that applying an electric field along any of the three Cartesian axes leads to a kinetic and thermodynamic effect favoring the cis β-lactam products over the trans, mirroring the reaction without an external electric field. Remarkably, our results also showed that the effects of OEEFs along the Y-axis is the sole contributor to enantioselectivity control. Thus, we observed that in the Staudinger reaction between tert-butylcyanoketene and benzylideneaniline, the OEEF influences the kinetics, thermodynamics and enantioselectivity, while the diastereoselectivity remains unaffected.