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I'm having trouble with the products of these reactions below... I feel like I'm on the right track but don't know why it comes up wrong enter image description here

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Figured out the aldehyde - but not the ester one!

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  • $\begingroup$ Those reactions won't lead to cyclic structures $\endgroup$ – Lighthart Apr 5 '14 at 20:47
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I figured out the aldehyde answer - but not the ester one... what am I missing?

If in doubt - draw:

Claisen ester condensation

You might want to light a candle for Ludwig Claisen now ;)

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You abstract the alpha-proton to make the alpha-anion stabilized by its enolate tautomer. There is nothing intramolecular past that, so it is intermolecular. In the ester case, the alpha anion displaces ethoxide into the 1,3-diketo system that is stabilized by abstraction of one of its now quite acidic 1,3-diketo protons. For the aldehyde, you add to another carbonyl then eliminate the alcohol/alkoxide to the conjugated olefin. Will it be ${E}$ or ${Z}$?

All carbonyl condensations are fundamentally the same. Look for the footnotes. It is easier to keep track of the inert structure hanging off as "R." Why is there no stereochemistry?

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  • $\begingroup$ I figured out the aldehyde answer - but not the ester one... what am I missing? $\endgroup$ – Harry Johnson Apr 5 '14 at 22:19
  • $\begingroup$ What is the leaving group? $\endgroup$ – Lighthart Apr 5 '14 at 22:25
  • $\begingroup$ "the alpha anion displaces ethoxide," above. Synthesis can be difficult, mechanism is easy. "All carbonyl condensations are fundamentally the same." Conditions change to optimize yield and cost of yield. Powdered KOH in neat pyridine does amazing condensations - in a beaker, covered with plastic wrap. It sounds awful but it's mighty cheap, and the pyridine recycles. Think "Pfaudler kettle." $\endgroup$ – Uncle Al Apr 7 '14 at 16:07
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Figured it out - basically add an (O-) to the olephin :)

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