Addition of Carbanions to a,3-Unsaturated Ketones The Michael Reaction

A synthetically useful reaction known as the Michael reaction, or Michael addition, involves nucleophilic addition of carbanions to a,(3-unsaturated ketones. The most common types of carbanions used are enolate ions derived from (3-diketones. These enolates are weak bases (Section 18.6) and react with a,(3-unsaturated ketones by conjugate addition. 

The product of Michael addition has the necessary functionality to undergo an intramolecular aldol condensation  

The synthesis of cyclohexenone derivatives by Michael addition followed by intramolecular aldol condensation is called the Robinson annulation, after Sir Robert Robinson, who popularized its use. By annulation we mean the building of a ring onto some starting molecule. (The alternative spelling aimelation is also often used.) 

PROBLEM 18.16 Both the conjugate addition step and the intramolecular aldol condensation step can be carried out in one synthetic operation without isolating any of the intermediates along the way. For example, consider the reaction 

Write structural formulas corresponding to the intermediates formed in the conjugate addition step and in the aldol addition step. 

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