Question

What two carbonyl compounds are needed to synthesize each of the following compounds, using a Robinson annulation?

Short answer

1. The two carbonyl carbon compounds needed to synthesize (a) arebuta-3-en-2-one and methyl butan-3-on-ate.
2. The two carbonyl carbon compounds needed to synthesize (b) are pent-1-en-3-on and methyl 3-oxopropanoate.
3. The two carbonyl carbon compounds needed to synthesize (c) are pent-1-en-one and 2-methylcyclohexane-1,3-dione.

Step-by-step solution

Carbonyl compound for synthesizing compound (a)

Carbonyl compounds (starting materials) needed for synthesizing compound (a) by a Robinson annulation is done by drawing a line that bisects both the double bond and the bond between the beta-carbon and gamma-carbon on the other side of the molecule.α,ß-unsaturated

• The beta-carbon comes from theα,ß-unsaturatedcarbonyl compound i.e., buta-3-en-2-one.
• The gamma-carbon is the alpha-carbon of the enolate ion of the dicarbonyl compound, that adds to the beta-carbon in the Michael reaction i.e., methyl 3-oxobutanoate.

The formation of carbonyl compounds for compound (a), are shown below.

Carbonyl compounds forming compound (a)

Carbonyl compound for synthesizing compound (b)

Carbonyl compound (starting materials) needed for synthesizing compound (a) [l1] by a Robinson annulation is done by drawing a line that bisects both the double bond and the bond between the beta-carbon and gamma-carbon on the other side of the molecule.

• The beta-carbon comes from the α,ß-unsaturatedcarbonyl compound i.e., pent-1-en-3-one.
• The gamma-carbon is the alpha-carbon of the enolate ion of the dicarbonyl compound that adds to the beta-carbon in the Michael reaction i.e., methyl 3-oxopropanoate.

The formation of carbonyl compounds for compound (b) are shown below.

Carbonyl compounds forming compound (b)

Carbonyl compound for synthesizing compound (c)

Carbonyl compound (starting materials) needed for synthesizing compound (b) [l1] by a Robinson annulation is done by drawing a line that bisects both the double bond and the bond between the beta-carbon and gamma-carbon on the other side of the molecule.

• The beta-carbon comes from the α,ß-unsaturatedcarbonyl compound i.e., pent-1-en-one.
• The gamma-carbon is the alpha-carbon of the enolate ion of the dicarbonyl compound that adds to the beta-carbon in the Michael reaction i.e., 2-methylcyclohexane-1,3-dione.

The formation of carbonyl compound for compound (c) are shown below.

Carbonyl compounds forming compound (c)