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A CH20150 > Functional Group Interconversion > Flashcards

Functional Group Interconversion Flashcards

1
Q

What are the two types of retrosynthetic step

A
  1. Bond disconnection

2. FGI

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2
Q

Give three ways to oxidise an alcohol using chromium (VI) reagents and give their properties

A
  1. Jones’ reagent- harshest

2. PCC, PDC- milder reagents with better solubility in organic solvents

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3
Q

What will be produced from a primary alcohol using each of the chromium (VI) Reagents

A
  1. Jones’- carboxylic acid

2. PCC, PDC- aldehyde

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4
Q

What will be produced from a secondary alcohol using each of the chromium (VI) Reagents

A
  1. All produce a ketone
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5
Q

What is the main downside to chromium (VI) reagents

A
  1. They are all toxic and carcinogenic

2. The waste is expensive to dispose of

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6
Q

What is the most common activated DMSO oxidation

A
  1. Swern oxidation
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7
Q

Describe what is needed in a Swern oxidation and what is produced from different alcohols and byproduct

A
  1. Activating agent for DMSO is oxalyl chloride
  2. -78 degrees
  3. Ketone and aldehyde produced
  4. Byproduct- Me-S(II)-Me
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8
Q

What are other activating agents used in activated DMSO oxidations

A
  1. Parikh-Doering: pyridine-SO3

2. Pfitzner-Moffat: carbodiimide

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9
Q

Name 3 other more modern oxidising agents and say why they might be preferred

A
  1. Dess-Martin periodinane
  2. IBX
  3. TPAP (Ley-Griffith oxidation)
  4. Mild oxidising agents- neutral conditions so good for weaker alcohols
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10
Q

Does IBX or Dess-Martin have better solubility

A
  1. Dess-Martin
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11
Q

Describe IBX oxidation

A
  1. TPAP is the catalyst

2. NMO is the stoichiometric oxidant- as it is much cheaper

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12
Q

What are the 4 steps in a Swern oxidation

A
  1. Activation of DMSO by oxalyl chloride to form the sulfonium
  2. Attack on the sulfonium by the alcohol
  3. Formation of the ylide- molecule with +ve and -ve on adjacent atoms
  4. Formation of the product
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13
Q

What is the most powerful reductant for carbonyl functional groups

A
  1. Lithium Aluminium Hydride (LiAlH4)
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14
Q

What conditions are needed when using LiAlH4

A
  1. Reacts violently with water (and very violently with acid) so must be kept dry
  2. Reactions done in ethereal solvents (Et2O, THF, DME)
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15
Q

List everything LiAlH4 reduces

A
  1. Ketone–> secondary alcohol
  2. Aldehyde–> primary alcohol
  3. Carboxylic acid–> primary alcohol
  4. ester –> primary alcohol + primary alcohol
  5. Amide –> amine
  6. Nitrile –> amine
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16
Q

What does NaBH4 reduce

A
  1. Aldehydes and ketones

2. Not esters or amides

17
Q

What solvents can NaBH4 be used in

A
  1. Protic solvents- MeOH, EtOH but does react with them slowly
18
Q

What is an issue when reduced alpha,beta-unsaturated ketones

A
  1. There is a selectivity issue and several products are possible
  2. Hydride could add across the C=C bond or C=O
  3. Make saturated ketone and then saturated alcohol could be produced or just allyl alcohol
  4. Only reason C=C can be reduced is because it is conjugated by EWG C=O
19
Q

How can you ensure 1,2 reduction in alpha,beta unsaturated ketones

A
  1. Use the Luche reduction
  2. NaBH4/CeCl3
  3. Produces allyl alcohol only
20
Q

What is an electrophilic reducing agent

A
  1. DIBAL-H

2. Contains an electrophilic aluminium atom

21
Q

What does DIBAL-H produce from reduction of esters

A
  1. 1 eq + -78 degrees = aldehyde + primary alcohol- capricious
  2. 2eq + rt = primary alcohol + primary alcohol
22
Q

What is produced when DIBAL-H reduced alpha,beta unsaturated carbonyls

A
  1. Selectively reduced in a 1,2 fashion due to pre-coordination of the aluminium to the carbonyl carbon
23
Q

How is a nitrile group normally introduced into a molecule

A
  1. By nucleophilic substitution using a cyanide salt- NaCN, KCN etc
24
Q

What can a nitrile be converted into

A
  1. Carboxylic acid
  2. Primary amine
  3. Imine–> aldehyde
  4. imine –> ketone
25
Q

How can you convert a nitrile to a carboxylic acid

A
  1. H+ + H2O
26
Q

How can you convert a nitrile to a primary amine

A
  1. LiAlH4 or
  2. H2/ Raney Ni or
  3. Excess DIBAL
27
Q

How can you convert a nitrile to a ketone

A
  1. R’MgX –> imine

2. Hydrolysis of imine –> ketone

28
Q

How can you convert a nitrile to a aldehyde

A
  1. 1 eq DIBAL, -78 degrees –> imine

2. Hydrolysis of imine –> aldehyde

29
Q

What should you never mix C=-N with

A
  1. Bronsted acid

2. Produced HCN extremely toxic gas

30
Q

What can nitrile introduction be used to effect

A
  1. Homologation- extending a carbon chain
31
Q

How can you convert an alcohol into a halide

A
  1. A phosphine (PPh3) and the desired halogen (bromine or iodine)
  2. For chloride, alcohol can be treated with thionyl chloride or PPh3/CCl4- Appel reaction

A CH20150 (15 decks)

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