Functional Group Interconversions

Question 1

Convert Ester to Aldehyde

Answer 1

Issue - once some aldehyde formed in solution, it is more reactive and will be reduced by reducing agent.
- 1 way is to use DiBAL to completely reduce to alcohol then selectively oxidise using PCC OR SWERN OR TRAP/NMO

Question 2

Swern Oxidation

Answer 2

Primary or secondary alcohol oxidised to aldehyde or ketone (NOT CA) using Oxalyl chloride, dimethyl sulfoxide (DMSO) and organic base, e.g. ET3N

Question 3

Oxalyl Chloride

Answer 3

O=C(Cl)C=O(Cl)

Question 4

DMSO

Answer 4

Dimethyl sulfoxide (CH3)2SO - organic and water solvent. It’s a nucleophile but NOT A BASE (will not deprotonate OH)

Question 5

PCC

Answer 5

Pyridine (With + charge on N) and Cr(O3)Cl

Question 6

Compare pKa of acetone, ethyl ethanoate, ethyl 3-oxobutanoate (1,3 dicarboxylic acid with methyl group replaced by OEt)

Answer 6

Ethyl ethanoate - alpha carbon pKa = 25
Acetone, pKa alpha carbon roughly 20
1,3 dicarboxylic ester - H at alpha carbon of both carbonyl groups pKa = 12/13. Next deprotonated one is much harder - but that means if double enolate formed the second one will be much more reactive as its keto form more stable!

Question 7

Luche reduction

Answer 7

Lewis Acid (e.g. CeCl3 and NaBH4 which selectively reduces harder electrophile, e.g. the carbon on the carbonyl group in a michael acceptor molecule. Selective to ketones in presence of aldehydes or towards ketone on michael acceptor if other ketones present. (ALLYLIC POSITION)

Question 8

L Selectride

Answer 8

Reduces ketone to alcohol in syn reduction as substituent (axial?)

It is bulky (LiEt3BH), therefore attacks at equatorial position, and Oxygen gets pushed down leaving OH at axial position!

Question 9

Allylic Carbon

Answer 9

Carbon adjacent to double bond

Question 10

Synthesis of Diazonium salt

Answer 10

Nitration of benzene (using H2SO4 and HNO3), reduce to amine either with ZN AND ACID (or Fe or Sn) OR Pt, Pd or Ni cat and H2, then react with NaNO2 or NO2H and 2equiv HCl.

Question 11

Conversion of alkene to 1,2 syn diol

Answer 11

Os(O4) and hydrogen peroxide

Question 12

Diazonium salt to other group

Answer 12

React diazonium salt with CuX (X = CN, Br, Cl, SO3H) with heat.
I think will also work with water as nucleophile without heat or copper.
Nucleophilic aromatic substitution (leaving positive carbocation)

Question 13

After friedal crafts acylation, reduce to alkane group?

Answer 13

Wolff kishner [1. NH2NH2, -H20 2) Base]
OR
Clemmensen reduction
[ZN/Hg and HCl)

Question 14

Reduce ketone to imine with NH2 attached to N

Answer 14

NH2NH2, (loss of H2O)

Question 15

Ways to do Nucleophilic Aromatic Substitution

Answer 15

1. SnAR (direct attack and loss of leaving group)
2. Sn1 type, with diazonium salts that leave a carbocation intermediate
3. Formation of Benzyne using liq Nitrogen and NaNH2 (nucleophile). The alkyne must be formed where a LG was. Attack can occur at either carbons.

Question 16

How to fluorinate benzene ring

Answer 16

Difficult - maybe use diazonium salt and HBF4 and heat (HBF4 is used instead of HCl in diazonium salt formation)

Question 17

Reduce NO2 to NH2 on aromatic ring

Answer 17

Zn/Hg and HCl

Question 18

Remove NH2 substituent on aromatic ring

Answer 18

1) NaNO2 and HCl (conversion to diazonium salt)
2) H3PO2 (source of protons, after diazonium salt leaves carbocation, can give H?)

Question 19

Remove aromaticity benzene

Answer 19

H2/Ni, high temp and pressure