Origin of stereocontrol in the Matteson reaction: Importance of attractive electrostatic interactions

The Matteson reaction involves treatment of a chiral boronic ester with (dichloromethyl)lithium in the presence of ZnCl2 which leads to an α–chloroboronic ester with very high diastereoselectivity. The origin of selectivity has now been investigated using modern computational analysis. The explanation for selectivity was previously based on steric repulsions in the transition state but the new study has identified a novel Cl··H electrostatic interaction which is only present in one of the two possible transition states. It is believed that this attractive interaction is critical in controlling the stereochemical outcome of the process. Furthermore, this more complete model can now be used to rationalize the disparity in reactivity (C–migration vs O–migration) occasionally observed in diastereomeric boron ate complexes, and why substrates devoid of the key hydrogen bond react with low stereocontrol.