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Chapter 28 Suggested solutions for Chapter 28 223 Problem 3 The of corylone was outlined in the chapter but no mechanistic details were given. Suggest mechanisms for the first The last step is a very unusual type of reaction and you have not met anything quite like it before. However, organic should be able to draw mechanisms for new reactions and you might like to try your hand at this one. There are steps. CI CI 0 5% HCI CO₂Me 1. NaOMe Cl₂ 0 15% HOAc OH CO₂Me 2. Mel Me HOAc Me CO₂Me dimethyl CO₂Me Me adipate 85% yield 98% yield 68% yield of the problem revision of mechanisms and a check that you realize what is the exact product of the Claisen densation under the reaction conditions. solution step is an intramolecular condensation between two identical esters (sometimes called the condensation). Under the reaction conditions the product is the stable enolate of the The base used is methoxide and this is strong enough about 16) to form the of a about 12). This enolate is alkylated in this sequence before the usual acid work-up. CO₂Me 1. NaOMe CO₂Me 2. Mel Me CO₂Me CO₂Me is a straightforward chlorination of an enol (note enol not enolate as the catalyst as described in Chapter 21. The only unusual thing is that enough chlorine is used to get chlorination. As explained in Chapter 21, this is slower than the first but is no trouble here enolizing positions are blocked. CI CI CI H CI CI 0 HOAc OH 0 0 repeat Me Me Me Me CO₂Me CO₂Me CO₂Me CO₂Me were warned that the last step would be weird but at least the hydrolysis and decarboxylation are We hope you remembered to use the cyclic mechanism for the decarboxylation step. CI CI CI CI 5% HCI CI CI CI CI 15% HOAc 0 0 H OH 0 Me 0 CO₂Me Me Me Me 0 product will mainly exist in the more stable keto-form but the unusual hydrolysis of the to the ketone might be easier in the enol form. Loss of a chloride in an SN1 reaction 17) gives a stable allylic cation. The second chloride is lost more easily because the OH