This document discusses different methods for asymmetric synthesis, which is the production of a single enantiomer from an achiral starting material. It describes chiral pool synthesis, which uses naturally occurring chiral compounds as starting materials. It also explains chiral auxiliaries, where an enantiopure auxiliary is attached and later removed, leaving the desired enantiomer. Chiral reagents and chiral catalysts are also discussed, where an enantiopure reagent or catalyst leads to an enantioselective reaction. Specific examples include the use of chiral boron hydrides and ligands like BINAP. Asymmetric hydrogenation is given as another key method. The document emphasizes the importance of these techniques for drug safety and mimicking nature.

1. SHIKHA D. POPALI
HARSHPAL SINGH WAHI
GURUNANAK COLLEGE OF PHARMACY, NAGPUR

2. Introduction
 The direct synthesis of an optically active substance from
actively inactive substance(compound) with or without the
use of optically active reagents is called as asymmetric
synthesis.
 Production of a specific enantiomer from achiral compound or
racemic mixture.
 A laboratory synthesis of a chiral compound from achiral or
racemic starting materials alone always gives a racemic
mixture of enantiomers.
 If you want to make just one enantiomer, you have to use a
starting material or reagent which is also just one enantiomer.
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3. CHIRAL POOL SYNTHESIS
 simplest and oldest approaches for enantioselective
synthesis,
 Uses an enantiomerically pure natural product as a starting
material,
 The chiral pool—Nature’s ‘ready-made’ chiral centres :pure
natural products, usually amino acids or sugars, from which
pieces containing the required chiral centres can be taken
and incorporated into the product.
 Aspartame from s- phenylanine and s- aspatic acid.
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4. CHIRAL AUXILIARIES
 An enantiomerically pure compound (usually derived from a
simple natural product like an amino acid), called a chiral
auxiliary, is attached to the starting material.
 A diastereoselective reaction is carried out, which, because
of the enantiomeric purity of the chiral auxiliary, gives only
one enantiomer of the product.
 The chiral auxiliary is removed by, for example, hydrolysis,
leaving the product of the reaction as a single enantiomer.
 The best chiral auxiliaries can be recycled, so although
stoichiometric quantities are needed, there is no waste.
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5. Flow chart of the chiral auxiliary strategy
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6.  An example
Diel’s Alder reaction between cyclopentadiene benzyl acrylate
Chiral auxiliary : amide derived from valine via reaction to give
asymmetric product
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7. CHIRAL REAGENTS AND CHIRAL CATALYSTS
 Chiral reagent: enantio specific product
 E.g. chiral boron hydride (CBS)
Corey, Bakshi, Shibitha
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8. Enantio selective catalysts
 enantioselective catalysis are chiral coordination
compounds
 Ligands show chirality
 Privileged ligands :(2,2'-bis(diphenylphosphino)-1,1'-
binaphthyl( BINAP),BINOL
R- BINAP S- BINAP
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9. ASYMMETRIC HYDROGENATION
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11. conclusion
 Drug safety
 Pharmaceuticals
 Flavours
 Mimic nature
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12. Reference
 Clayden, Jonathan, Nick Greeves and Stuart Warren.
Organic Chemistry, 2nd Edition. Oxford. 2012.
 Finar, I. L. Organic Chemistry : Stereo Chemistry and
Chemistry of Natural Products (vol:2), 5th Edition.
Dorling Kindersley Pvt. Ltd. Noida, India. 1975.
 Nasipuri, D. Stereochemistry of Organic Compounds:
Principles and Applications, 2nd Edition. New Age
International Pvt. Ltd. New Delhi. 1994
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13. Thank you
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