CBS catalyst

It transfers its stereocenter to the catalyst which in turn is able to drive an organic reaction selectively to one of two possible enantiomers.

This selectivity is due to steric strain in the transition state that develops for one enantiomer but not for the other.

The CBS catalyst can be prepared from diphenylprolinol,[1] condensed with a phenylboronic acid, or with borane (as shown below).

The first leg of the reaction sequence starts from the azeotropic dehydration of a boronic acid (1) such as one based on toluene to a boroxine (2).

This boroxine reacts with the proline derivative (3d) to form the basic oxazaborolidine CBS catalyst (4).