Case Study Asymmetric Alkylation of Benzaldehyde

Synopsis of Goldfuss and Houk (1998) Origin of Enantioselectivities in Chiral /3-Amino Alcohol Catalyzed Asymmetric Additions of Organozinc Reagents to Benzaldehyde PM3 Transition State Modeling . 

When the /6-amino alcohol ligand is chiral and optically pure, there are four potentially low-energy TS structures that may lead to products. Several chiral ligands have been shown 

I be observed. At least four other TS structures can be readily imagined while maintaining the atomic connectivities of those shown here. What are they and why might they be intuitively discounted Are there still other TS structures one might imagine How does one decide when all relevant TS structures have been considered  

---