Simple Diastereoselection Chair vs. Boat Transition States

Simple Diastereoselection Chair vs. Boat Transition States 

A key aspect of stereoselectivity in the Ireland-Claisen rearrangement is the preferential formation of syn (erythro) or anti (threo) pentenoic acids from appropriately substituted allyl silyl ketene acetals. The stereochemical outcome of the reaction is determined by two features (1) the geometry of the silyl ketene acetal and aUyUc alkene, and (2) whether the rearrangement proceeds via a chair-like or boat-Uke transition state. 

---