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FGIs
- 1. RETROSYNTHETIC APPROCH TO ORGANIC SYNTHESIS FUNCTIONAL GROUP INTERCONVERSION Dr. Shaikh S. Nizami Department of Chemistry University of Karachi
- 2. FUNCTIONAL GROUPS INTERCONVERSIONS
- 3. CONTENTS Definition of Functional Group Interconversion (FGIs) Importance of FGIs Functional group containing heteroatoms Unsaturated hydrocarbons Removal of Functional Groups
- 4. Definition of F unctional G roup I nterconversion The process of writing one functional group for another to help synthetic planning is known as FGI
- 5. Definition of F unctional G roup I nterconversion FGI can be done by Substitution Addition Elimination Oxidation Reduction
- 6. Why FGI is needed? A TM containing more than one functional group, one functional group may interfere with desired reaction on second functional group during a synthesis.
- 7. Why FGI is needed? This problem can be solved into ways a) Use of protecting group b) Change in synthetic strategy (using FGI)
- 8. Importance of FGIs It helps in identifying suitable disconnection. Consider the synthesis of ketone containing a double bond. Alkenes may be prepared by the dehydration of alcohol.
- 9. Importance of FGIs TM First step in the retrosynthetic analysis of TM could be functional group interconversion to an alcohol But which alcohol ?
- 10. Importance of FGIs FGI i FGI ii TM
- 11. RETROSYNTESIS FGI + TM Matched Latent Polarity (Consonant) i
- 12. RETROSYNTESIS FGI ii Mismatched Latent Polarity (Dissonant)
- 13. Functional group containing heteroatoms For convenience these functional groups will be initially divided into three major classes depending upon their oxidation level
- 14. a) Carboxylic acid and their derivatives Compounds in this class are the highest oxidation level of organic compounds It includes Carboxylic acid (RCO 2 H) Esters/lactone (RCOO 2 R) Amide/lactam (RCONHR) They may be interconverted by a series of simple reactions
- 15. Transformations of carboxylic acid derivatives SOCl 2 or PCl 5 H 2 O NH 3 RO - H 2 O H 2 O H + / R’OH H 2 O
- 16. b) Aldehydes, ketones and their derivatives Functional groups in this class are at lower oxidation level than class (a) It includes the features C=X in which the carbon atom is bonded directly to either hydrogen or carbon.
- 17. b) Aldehydes, ketones and their derivatives The group includes Aldehydes (RHC=O) Ketones (RR’C=O) Imines (RR’C=NR”) Hydrazones (RR’C=NNHR”) Oximes (RR’C=NOH)
- 18. Transformations of aldehydes aldehyde R’NH 2 R’=alkyl, aryl,(imine) R’=NMe2 (hydrazones) R’=OH (oxime) H 2 O HS(CH 2 ) 3 SH/H+ 2R’OH/H +
- 19. c) Alcohols and their derivatives Apart from Alcohols (ROH) themselves, this class includes Amines (RNH2) Thiols (RSH) Disulphides (RSSR) Ethers (ROR) Alkyl halides (RX)
- 20. Interconversions of alcohols and halides SOCl2 or PCl5 HO - HBr HO -
- 21. Use of a sulphonic ester as a leaving group R’SO 2 Cl Nu - + R’SO 3 -
- 22. Interconversions between the three oxidation levels a,b & c above To move between groups classified in the previous section, it is necessary to perform a reduction or oxidation at some stage.
- 23. Oxidation Many methods have been developed for the oxidation of organic compounds. It is possible to transform a low oxidation level FG into any group of higher level.
- 24. Oxidation Primary alcohol PCC or PDC CrO 3 /H + Secondary alcohol PCC or PDC PCC= pyridinium chlorochromate PDC= pyridinium dichromate
- 25. Reduction Esters LiAlH 4 + R’OH Amides LiAlH 4 Nitriles LiAlH 4 1 eq. DIBAL-H Low temp.
- 26. Unsaturated Hydrocarbons H 2 ,Pd/C OsO 4 O 3 HBr RCO 3 H BH 3 ,NaOH/ H2O 2
- 27. Removal of Functional Group Alcohol to corresponding hydrocarbon Alcohol Dehydration Alkene Alkane Hydrogenation
- 28. Removal of Functional Group Clemmensen Wolf-Kishner Zn,HCl NH 2 NH 2 ,KOH Aldehydes/ ketones to hydrocarbons