Question

Provide the reagents necessary to carry out the following conversion.

1. HOCH2CH2OH/H2SO4
2. LiAlH4
3. CH3CH2MgBr (2 eq)
1. H2SO4
2. CH3CH2OH
3. H3O
1. HOCH2CH2OH/H2SO4
2. CH3CH2MgBr (2 eq)
3. H3O

Answer 1

1. HOCH₂CH₂OH/H₂SO₄

2. CH₃CH₂MgBr (2 eq)

3. H₃O⁺

Step-by-step explanation:

Assume the conversion is the one in the first Figure.

You want to convert the ester to a 3° alcohol.

However, you must first protect the ketone from reacting.

(i) React the compound with ethylene glycol and sulfuric acid. The ketone is converted to a cyclic acetal.

(ii). Add two molar equivalents of ethylmagnesium bromide. Two moles of the Grignard reagent convert the ester into the magnesium salt of a 3° alcohol.

(iii) Aqueous acid removes the protecting group and converts the salt to an alcohol.

The first set of options is wrong. LiAlH₄ reduces the ester to a 1° alcohol.

The second set of options is wrong. Concentrated sulfuric acid won't do anything. Aqueous sulfuric acid will hydrolyze the ester to methanol and a carboxylic acid. Ethanol will convert the acid to an ethyl ester, but aqueous acid will hydrolyze it again.