An improved mechanistic model for the diastereoselective addition of Grignard reagents to -(-butylsulfinyl)imines.

The mechanism of the diastereoselective addition of ethylmagnesium bromide to ()--benzylidene-2-methylpropane-2-sulfinamide in CHCl has been studied by DFT calculations using a model that involves an explicit molecule of diethyl ether (coming from the Grignard reagent solution) coordinated to the magnesium atom. Several reaction pathways have been investigated and the energy profiles obtained for the preferred routes lead to an estimated diastereomeric ratio that matches very well with the experimental data. This new mechanistic model gives a plausible explanation of the diastereoselectivity obtained in the reaction.