Asymmetric synthesis

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.

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

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

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

Asymmetric synthesis

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Asymmetric synthesis