The document discusses four generations of asymmetric synthesis techniques: 1) First generation uses a chiral substrate to control the formation of new chiral centers through diastereoselective reactions. 2) Second generation uses a chiral auxiliary covalently attached to the substrate to control asymmetric induction. 3) Third generation uses a chiral reagent or catalyst to induce asymmetry through intermolecular interactions. 4) Fourth generation involves catalytic versions of the first three generations and reactions where two new stereocenters are formed in one step, often using a chiral substrate and reagent.

11. DKR

12. Generations in Asymmetric Synthesis
1st
Generation – Substrate-controlled Asymmetric synthesis
Diastereoselective reactions where the formation of a chiral centre is
controlled by another chiral centre already present in the substrate.
2nd
generation – Auxiliary-controlled Asymmetric synthesis
Methods where a chiral auxiliary is covalently attached to the substrate
and, through that, controls the asymmetric induction. This strategy, with
intermolecular controlled induction, is basically the same in first- and
second-generation methods. The difference is the attachment and removal
of the auxiliary in the latter.
3rd
generation – Reagent-controlled Asymmetric synthesis
The formation of a new chiral centre is induced by a chiral reagent or
catalyst, intermolecularly.
4th
Generation – Catalyst-controlled Asymmetric synthesis
Catalytic modifications of the first-, second-, and third-generation methods
tend to be considered together with this new fourth-generation. One
general procedure involves a reaction of a chiral substrate with a chiral
reagent, and is especially useful in reactions where two new stereogenic
units are formed stereo selectively in one step.

13. Overview of generations

15. This is what called as 1,2-asymmetric induction
2
1 2 1

16. How does the center control the direction of attack at the triagonal carbon ?
Cram’s Rule

19. Nature is a good chemist. It will give 100% e.e.

23. Any Questions !!!