What are the key steps in the Robinson annulation?

The key steps in the Robinson annulation are the Michael addition, aldol condensation, and dehydration.

The Robinson annulation is a chemical reaction used to create a six-membered ring from a ketone and a methyl vinyl ketone. This reaction is named after Sir Robert Robinson, a British organic chemist who won the Nobel Prize in Chemistry in 1947. The process involves three key steps: the Michael addition, aldol condensation, and dehydration.

The first step, the Michael addition, involves the addition of a nucleophile to an α,β-unsaturated carbonyl compound. In the case of the Robinson annulation, the nucleophile is a ketone and the α,β-unsaturated carbonyl compound is a methyl vinyl ketone. The ketone attacks the β-carbon of the methyl vinyl ketone, forming a new carbon-carbon bond and creating a 1,5-diketone.

The second step is the aldol condensation. This is an organic reaction in which an enolate ion reacts with another carbonyl compound to form a β-hydroxy carbonyl compound, also known as an aldol (aldehyde + alcohol). In the Robinson annulation, the enolate ion formed in the Michael addition reacts with the carbonyl group of the 1,5-diketone, forming a new six-membered ring.

The final step is dehydration, which involves the removal of a water molecule. This step is facilitated by heating the reaction mixture. The β-hydroxy carbonyl compound formed in the aldol condensation loses a water molecule, resulting in the formation of a double bond and the final product, a cyclohexenone.

In summary, the Robinson annulation is a complex reaction that involves the formation of a six-membered ring from a ketone and a methyl vinyl ketone. The key steps are the Michael addition, aldol condensation, and dehydration. This reaction is a powerful tool in organic chemistry, allowing for the synthesis of complex cyclic structures.