Functional Group Interconversion Flashcards
What are the two types of retrosynthetic step
- Bond disconnection
2. FGI
Give three ways to oxidise an alcohol using chromium (VI) reagents and give their properties
- Jones’ reagent- harshest
2. PCC, PDC- milder reagents with better solubility in organic solvents
What will be produced from a primary alcohol using each of the chromium (VI) Reagents
- Jones’- carboxylic acid
2. PCC, PDC- aldehyde
What will be produced from a secondary alcohol using each of the chromium (VI) Reagents
- All produce a ketone
What is the main downside to chromium (VI) reagents
- They are all toxic and carcinogenic
2. The waste is expensive to dispose of
What is the most common activated DMSO oxidation
- Swern oxidation
Describe what is needed in a Swern oxidation and what is produced from different alcohols and byproduct
- Activating agent for DMSO is oxalyl chloride
- -78 degrees
- Ketone and aldehyde produced
- Byproduct- Me-S(II)-Me
What are other activating agents used in activated DMSO oxidations
- Parikh-Doering: pyridine-SO3
2. Pfitzner-Moffat: carbodiimide
Name 3 other more modern oxidising agents and say why they might be preferred
- Dess-Martin periodinane
- IBX
- TPAP (Ley-Griffith oxidation)
- Mild oxidising agents- neutral conditions so good for weaker alcohols
Does IBX or Dess-Martin have better solubility
- Dess-Martin
Describe IBX oxidation
- TPAP is the catalyst
2. NMO is the stoichiometric oxidant- as it is much cheaper
What are the 4 steps in a Swern oxidation
- Activation of DMSO by oxalyl chloride to form the sulfonium
- Attack on the sulfonium by the alcohol
- Formation of the ylide- molecule with +ve and -ve on adjacent atoms
- Formation of the product
What is the most powerful reductant for carbonyl functional groups
- Lithium Aluminium Hydride (LiAlH4)
What conditions are needed when using LiAlH4
- Reacts violently with water (and very violently with acid) so must be kept dry
- Reactions done in ethereal solvents (Et2O, THF, DME)
List everything LiAlH4 reduces
- Ketone–> secondary alcohol
- Aldehyde–> primary alcohol
- Carboxylic acid–> primary alcohol
- ester –> primary alcohol + primary alcohol
- Amide –> amine
- Nitrile –> amine
What does NaBH4 reduce
- Aldehydes and ketones
2. Not esters or amides
What solvents can NaBH4 be used in
- Protic solvents- MeOH, EtOH but does react with them slowly
What is an issue when reduced alpha,beta-unsaturated ketones
- There is a selectivity issue and several products are possible
- Hydride could add across the C=C bond or C=O
- Make saturated ketone and then saturated alcohol could be produced or just allyl alcohol
- Only reason C=C can be reduced is because it is conjugated by EWG C=O
How can you ensure 1,2 reduction in alpha,beta unsaturated ketones
- Use the Luche reduction
- NaBH4/CeCl3
- Produces allyl alcohol only
What is an electrophilic reducing agent
- DIBAL-H
2. Contains an electrophilic aluminium atom
What does DIBAL-H produce from reduction of esters
- 1 eq + -78 degrees = aldehyde + primary alcohol- capricious
- 2eq + rt = primary alcohol + primary alcohol
What is produced when DIBAL-H reduced alpha,beta unsaturated carbonyls
- Selectively reduced in a 1,2 fashion due to pre-coordination of the aluminium to the carbonyl carbon
How is a nitrile group normally introduced into a molecule
- By nucleophilic substitution using a cyanide salt- NaCN, KCN etc
What can a nitrile be converted into
- Carboxylic acid
- Primary amine
- Imine–> aldehyde
- imine –> ketone
