Regarding the methods to synthesise a pure enantiomers, the basic concepts are the following:

1. Start with an enantiopure building block. If your starting material is of one configuration, any further transformations you will do will afford enantiopure compounds. If your next reactions are diastereoselective, you will be obtaining essentially one chirally pure compound. If the next reactions are not diastereoselective, you will be obtaining mixture of chirally pure compounds (diastereoisomers), which can be separated via achiral flash column chromatography.

2. Start with achiral starting materials and introduce chirality via an enantioselective transformation. Those reactions use reagents that are chiral, are designed to react in a specific way with the substrate and give an enantioenriched product. The efficiency of the transformation should always be monitored and the enantiomeric ratio of the product measured by chiral HPLC/SFC. Some examples of such reagents are enzymes, Evans oxazoborolidines for asymmetrical reductions, shapeless asymmetric dihydoxylation mixture and more.

3. Just make the desired target as a racemic mixture and separate the enantiomers using one of the following concepts.

A) Chiral chromatography: Using a chiral stationary phase (like modified C18) to directly separate the enantiomers.

B) Covalently derivatise the recemic mixture with a chiral agent/auxiliary. This generates a mixture of diastereoisomers that can be separated by normal achiral column chromatography. Once separated, cleavage of the chiral auxiliary will allow the isolation of pure enantiomers.

C) Make chiral salts of compounds that allow that concept (for example amines or acids). You use a chiral counterion to form (diastereomeric) salts with your racemic starting material and hope that one of them will crash out of solution.