Protecting Groups (Examples)
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The document discusses retrosynthetic analysis and protecting groups in organic synthesis. It provides 4 examples of retrosynthetic analysis where the forward synthesis is deduced by working backwards from the target molecule. The examples show how protecting carbonyl and hydroxyl groups is necessary to allow for certain reactions like Grignard and Friedel-Crafts reactions to produce the target molecule.
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Protecting Groups (Examples)
- 1. RETROSYNTHETIC APPROCH TO ORGANIC SYNTHESIS PROTECTING GROUPS EXAMPLES Dr. Shaikh S. Nizami Department of Chemistry University of Karachi
- 2. EXAMPLE-01 RETROSYNTHETIC ANALYSIS FGI + MeI 1 10 11
- 4. EXAMPLE-01 SYNTHESIS + PBr 3 NaNH 2 MeI Na/NH 3 H 3 O+/Ac 2 O TM
- 5. EXAMPLE-02 RETROSYNTHETIC ANALYSIS i + ii + + i ii
- 6. EXAMPLE-02 SYNTHESIS MeCOCl AlCl 3 HBr Mg Et 2 O H 3 O + TM
- 7. Conversion of acid from bromo compound Overall reaction Cyanide displacement Not possible due to two -methyl group Grignard reagent can not be used because carbonyl group is also present in bromo compound Solution 1. Protect carbonyl group as ketal 2. Use Grignard reagent 3. Hydrolyzed the ketal group to ketone
- 8. SYNTHESIS i) Mg/ether ii) CO 2 iii) H 3 O +
- 9. EXAMPLE-03 RETROSYNTHETIC ANALYSIS + FGI TM is coronary vasodilator- Benziodarone TM
- 10. EXAMPLE-03 SYNTHESIS Protection of hydroxyl group is necessary before Fried-Crafts reaction is carried out Me 2 SO 4 SOCl 2 Pyr. HCl I 2 TM
- 11. EXAMPLE-04 RETROSYNTHETIC ANALYSIS TM Asthma drug - Salbutamol + H 2 NBu-t +
- 12. EXAMPLE-04 Synthesis CH 2 O Me 3 S + DMSO/ NaH t-BuNH 2 H 3 O + TM