A Chair-Like Transition State for the Aldol Reaction
The aldol reaction shown here often proceeds with good to excellent diastereospecificity. A chair-like transition state, modeled below, is proposed
In this model, carbon atoms are dark gray, hydrogen is cyan, oxygen is red and the metal species M is green. Ligands on the metal are yellow, the E and Z substituents on the enolate are light gray, and other alkyl substituents R are colored tan. The newly forming bonds are colored violet. The oxygen bonds to the metal are an important factor in organizing and stabilizing the transition state. When the metal is lithium, the ligands are often solvent molecules and the bonds to oxygen are long and relatively weak. When the metal is boron, the ligands are alkyl groups and the bonds to oxygen are shorter and stronger.
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