Q.26. - Organic Chemistry

Question

Question: Which of the following bicyclic ring systems can be prepared by an intermolecular Robinson annulation?

Step-by-Step Solution

Answer

Answer

The structures A, B, and C can be formed by intermolecular Robinson Annulation. 

Step 1: Robinson Annulation

This method involves the formation of a six-membered ring by the reaction of an $\beta$ unsaturated carbonyl and an enolate compound. In this reaction, 2 new σ and 1 new π-bonds are formed. 

Step 2: Break the cyclohex-2-enone ring into two components

Break the C=C bond and the bond between the $\mathit{\beta }$-carbon and the carbon next to it. If the compound can be broken into an $\mathit{\alpha }\mathbf{,}\mathit{\beta }\mathbf{-}$unsaturated carbonyl and an enolate compound, the compound can be formed by the Robinson Annulation.

Step 3: Compounds needed for Robinson Annulation

a. The compound can be broken to form the two starting materials required for this reaction. Hence, this compound can be formed by the Robinson Annulation method. 

b. The compound can be broken to form the two starting materials required for this reaction. Hence, this compound can be formed by the Robinson Annulation method. 

c. The compound can be broken to form the two starting materials required for this reaction. Hence, this compound can be formed by the Robinson Annulation method. 

d. The C=C to be broken to form one of the two starting materials, i.e., the enolate compound required for this reaction is not present in the given compound. Hence, this compound cannot be formed by the Robinson Annulation method.