Diastereoselective Additions of Allylmagnesium Reagents to alpha-Substituted Ketones When Stereochemical Models Cannot Be Used

The stereoselectivities of reactions of allylmagnesium reagents with chiral ketones cannot be easily explained by stereochemical models. Competition experiments indicate that the complexation step is not reversible, so nucleophiles cannot access the widest range of possible encounter complexes and therefore cannot be analyzed easily using available models. Nevertheless, additions of allylmagnesium reagents to a ketone can still be stereoselective provided that the carbonyl group adopts a conformation that leads to one face being completely blocked from the approach of the allylmagnesium reagent.

Automated summary

The stereoselectivities of reactions of allylmagnesium reagents with chiral ketones cannot be easily explained by stereochemical models, as observed in competition experiments. The irreversibility of the complexation step prevents nucleophiles from accessing a wide range of possible encounter complexes, making analysis using available models difficult. Nevertheless, stereoselective additions of allylmagnesium reagents to ketones can still occur if the carbonyl group adopts a conformation blocking one face from the approach of the reagent.