Module 1 : Reactions using Chiral Lewis Acids and Brønsted Acids

Lecture 1: Reactions Using Chiral Lewis and Brønsted Acids I

1.1.5 Modified BLA Catalysts

The following modified BLA catalysts 1d-e has been subsequently developed. These catalysts have also been demonstrated as powerful catalysts for Diels-Alder reactions.

1.2. Lewis Acid-Assisted Lewis Acid (LLA)

In Lewis acid assisted chiral Lewis acids (LLAs), achiral Lewis acid is added to activate chiral Lewis acid via complex formation. The reactivity of LLA is much greater compared to that of achiral Lewis acid, and thus, the latter's presence does not affect the selectivity of the reaction.

1.2.1 Diels-Alder Reaction

The LLA 2a , derived from chiral valine-based oxazaborolidine and SnCl4 as an activator, has been utilized as an efficient catalyst the for Diels-Alder reaction of wide range of substrates (Scheme 10). In this system, the LLA 2a is more reactive compared to SnCl4 and the ee is not affected because of the addition of excess SnCl4.

Additional examples:

Scheme 10